| 1. |
- de Jong, Roelof S., et al.
(författare)
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4MOST-4-metre Multi-Object Spectroscopic Telescope
- 2014
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Ingår i: Ground-based and Airborne Instrumentation for Astronomy V. - : SPIE. - 0277-786X .- 1996-756X. ; 9147
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Konferensbidrag (refereegranskat)abstract
- 4MOST is a wide-field, high-multiplex spectroscopic survey facility under development for the VISTA telescope of the European Southern Observatory (ESO). Its main science drivers are in the fields of galactic archeology, high-energy physics, galaxy evolution and cosmology. 4MOST will in particular provide the spectroscopic complements to the large area surveys coming from space missions like Gaia, eROSITA, Euclid, and PLATO and from ground-based facilities like VISTA, VST, DES, LSST and SKA. The 4MOST baseline concept features a 2.5 degree diameter field-of-view with similar to 2400 fibres in the focal surface that are configured by a fibre positioner based on the tilting spine principle. The fibres feed two types of spectrographs; similar to 1600 fibres go to two spectrographs with resolution R> 5000 (lambda similar to 390-930 nm) and similar to 800 fibres to a spectrograph with R> 18,000 (lambda similar to 392-437 nm & 515-572 nm & 605-675 nm). Both types of spectrographs are fixed-configuration, three-channel spectrographs. 4MOST will have an unique operations concept in which 5 year public surveys from both the consortium and the ESO community will be combined and observed in parallel during each exposure, resulting in more than 25 million spectra of targets spread over a large fraction of the southern sky. The 4MOST Facility Simulator (4FS) was developed to demonstrate the feasibility of this observing concept. 4MOST has been accepted for implementation by ESO with operations expected to start by the end of 2020. This paper provides a top-level overview of the 4MOST facility, while other papers in these proceedings provide more detailed descriptions of the instrument concept[1], the instrument requirements development[2], the systems engineering implementation[3], the instrument model[4], the fibre positioner concepts[5], the fibre feed[6], and the spectrographs[7].
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| 2. |
- Haynes, Roger, et al.
(författare)
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The 4MOST instrument concept overview
- 2014
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Ingår i: Ground-based and Airborne Instrumentation for Astronomy V. - : SPIE. - 0277-786X .- 1996-756X. ; 9147, s. 91476-91476
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Konferensbidrag (refereegranskat)abstract
- The 4MOST([1]) instrument is a concept for a wide-field, fibre-fed high multiplex spectroscopic instrument facility on the ESO VISTA telescope designed to perform a massive (initially >25x10(6) spectra in 5 years) combined all-sky public survey. The main science drivers are: Gaia follow up of chemo-dynamical structure of the Milky Way, stellar radial velocities, parameters and abundances, chemical tagging; eROSITA follow up of cosmology with x-ray clusters of galaxies, X-ray AGN/galaxy evolution to z similar to 5, Galactic X-ray sources and resolving the Galactic edge; Euclid/LSST/SKA and other survey follow up of Dark Energy, Galaxy evolution and transients. The surveys will be undertaken simultaneously requiring: highly advanced targeting and scheduling software, also comprehensive data reduction and analysis tools to produce high-level data products. The instrument will allow simultaneous observations of similar to 1600 targets at R similar to 5,000 from 390-900nm and similar to 800 targets at R>18,000 in three channels between similar to 395-675nm (channel bandwidth: 45nm blue, 57nm green and 69nm red) over a hexagonal field of view of similar to 4.1 degrees2. The initial 5-year 4MOST survey is currently expect to start in 2020. We provide and overview of the 4MOST systems: opto-mechanical, control, data management and operations concepts; and initial performance estimates.
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| 3. |
- Ivanov, Sergey A., et al.
(författare)
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Chemical pressure effects on structural, dielectric and magnetic properties of solid solutions Mn3-xCoxTeO6
- 2014
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Ingår i: Materials research bulletin. - : Elsevier BV. - 0025-5408 .- 1873-4227. ; 50, s. 42-56
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Tidskriftsartikel (refereegranskat)abstract
- The effects of Co2+ doping on the structural, magnetic and dielectric properties of the multiferroic frustrated antiferromagnet Mn3TeO6 have been investigated. Ceramic samples of the solid solution series Mn3-xCoxTeO6 were prepared by a solid-state reaction route. X-ray and neutron powder diffraction and electron microscopy techniques were combined with calorimetric, dielectric and magnetic measurements to investigate the dependence of the crystal structure and physical properties on temperature and composition. It is shown that the compounds with x <= 2.4 adopt the trigonal corundum-related structure of pure Mn3TeO6 (space group 18) in the temperature range 5-295 K and that the lattice parameters a and c and the unit-cell volume V decrease linearly with increasing Co2+ concentration. The low-temperature magnetic susceptibility and heat capacity data evidence the antiferromagnetic ordering of all samples. The Neel temperature linearly increases with Co2+ concentration x. Curie-Weiss fits of the high temperature susceptibility indicate that the magnetic frustration decreases with x. The derived magnetic structure of Mn3TeO6 can be described as an incommensurately modulated magnetic spin state with k = [0, 0, k(z)] and an elliptical spin-spiral order of spins within the chains of MnO6 octahedra. With increasing Co2+ concentration the propagation vector kz changes from 0.453 (x = 0) to 0.516 (x = 2.4). The magnetic anisotropy changes as well, leading to a reorientation of the spiral-basal plane. A possible coexistence of long-range order of electrical dipoles and magnetic moments in Mn3-xCoxTeO6 is discussed.
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| 4. |
- Ivanov, S. A., et al.
(författare)
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Neutron diffraction studies and the magnetism of an ordered perovskite : Ba2CoTeO6
- 2010
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 39:23, s. 5490-5499
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Tidskriftsartikel (refereegranskat)abstract
- The complex perovskite Ba2CoTeO6 (BCTO) has been synthesised, and the crystal structure and magnetic properties have been investigated using a combination of X-ray and neutron powder diffraction, electron microscopy and dielectric, calorimetric and magnetic measurements. It is shown that at room temperature this compound adopts the 6L-trigonal perovskite structure, space group P (3) over barm (s.g. 164) (a = 5.7996(1) angstrom, c = 14.2658(3) angstrom). The structure comprises dimers of face-sharing octahedra as well as octahedra which share only vertices with their neighbours. Dielectric measurements indicate a diffuse transition of antiferroelectric nature near 280 K. A long-range antiferromagnetically ordered state has been identified from neutron diffraction and magnetic studies. The magnetic diffraction peaks were registered below the magnetic transition at about 15 K and a possible model for the magnetic structure is proposed. The structural and magnetic features of this compound are discussed and compared with those of other Co-based quaternary oxides adopting the perovskite structure.
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| 5. |
- Ivanov, Sergey A., et al.
(författare)
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New type of incommensurate magnetic ordering in Mn(3)TeO(6)
- 2011
-
Ingår i: Materials research bulletin. - : Elsevier BV. - 0025-5408 .- 1873-4227. ; 46:11, s. 1870-1877
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Tidskriftsartikel (refereegranskat)abstract
- The complex metal oxide Mn(3)TeO(6) exhibits a corundum related structure and has been prepared both in forms of single crystals by chemical transport reactions and of polycrystalline powders by a solid state reaction route. The crystal structure and magnetic properties have been investigated using a combination of X-ray and neutron powder diffraction, electron microscopy, calorimetric and magnetic measurements. At room temperature this compound adopts a trigonal structure, space group R (3) over bar with a = 8.8679(1) angstrom. c = 10.6727(2) angstrom. A long-range magnetically ordered state is identified below 23 K. An unexpected feature of this magnetic structure is several types of Mn-chains. Under the action of the incommensurate magnetic propagation vector k = [0, 0, 0.4302(1)] the unique Mn site is split into two magnetically different orbits. One orbit forms a perfect helix with the spiral axis along the c-axis while the other orbit has a sine wave character along the c-axis.
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| 6. |
- Ivanov, Sergey A., et al.
(författare)
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Preparation, structural, dielectric and magnetic properties of LaFeO3-PbTiO3 solid solutions
- 2012
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Ingår i: Materials research bulletin. - : Elsevier BV. - 0025-5408 .- 1873-4227. ; 47:11, s. 3253-3268
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Tidskriftsartikel (refereegranskat)abstract
- Solid solutions of (1−x)LaFeO3–(x)PbTiO3 (0 < x < 1) have been prepared by conventional solid-state reaction. These complex perovskites have been studied by means of X-ray (XRPD) and neutron powder (NPD) diffraction, complemented with dielectric, magnetic, heat capacity and Mössbauer measurements. Complete solubility in the perovskite series was demonstrated. The NPD and XRPD patterns were successfully refined as orthorhombic (x ≤ 0.7) and tetragonal (x ≥ 0.8). A composition-driven phase transformation occurs within the interval 0.7 < x < 0.8. The samples with x < 0.5 showed evidence of long-range magnetic ordering with an G-type antiferromagnetic arrangement of the magnetic moments of the Fe3+ cations in the B-site with propagation vector k = (0,0,0). Based on the obtained experimental data, a combined structural and magnetic phase diagram has been constructed. The factors governing the structural, dielectric and magnetic properties of (1−x)LaFeO3–(x)PbTiO3 solid solutions are discussed, as well as their possible multiferroicity.
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| 7. |
- Ivanov, Sergey A., et al.
(författare)
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Spin and Dipole Ordering in Ni2InSbO6 and Ni2ScSbO6 with Corundum-Related Structure
- 2013
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 25:6, s. 935-945
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Tidskriftsartikel (refereegranskat)abstract
- The complex metal oxides Ni2InSbO6 (NISO) and Ni2ScSbO6 (NSSO) have been prepared in the form of polycrystalline powders by a solid state reaction route. The crystal structure and magnetic properties of the compounds were investigated using a combination of X-ray and neutron powder diffraction, electron microscopy, calorimetric, and magnetic measurements. The compounds adopt a trigonal structure, space group R3, of the corundum related Ni3TeO6 (NTO) type. Only one of the octahedral Ni positions (Ni(2)) of the NTO structure was found to be occupied by In (Sc). NTO has noncentrosymmetric structure and is ferroelectric below 1000 K; dielectric and second harmonic measurements suggest that also NISO and NSSO are correspondingly ferroelectric. Magnetization measurements signified antiferromagnetic ordering below T-N = 60 K (NSSO) and 76 K (NISO). The magnetic structure is formed by two antiferromagnetically coupled incommensurate helices with the spiral axis along the b-axis and propagation vector k = [0, k(y),0] with k(y) = 0.036(1) (NSSO) and k(y) = 0.029(1) (NISO). The observed structural and magnetic properties of NISO and NSSO are discussed and compared with those of NTO.
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| 8. |
- Ivanov, Sergey A, et al.
(författare)
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Structural and magnetic properties of Mn3-xCdxTeO6 (x = 0, 1, 1.5 and 2)
- 2012
-
Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 324:8, s. 1637-1644
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Tidskriftsartikel (refereegranskat)abstract
- Mn(3)TeO(6) exhibits a corundum-related A(3)TeO(6) structure and a complex magnetic structure involving two magnetic orbits for the Mn atoms [Ivanov et al., 2011 [3]]. Mn(3-x)Cd(x)TeO(6) (x = 0, 1, 1.5, and 2) ceramics were synthesized by solid state reaction and investigated using X-ray powder diffraction, electron microscopy, and calorimetric and magnetic measurements. Cd(2+) replaces Mn(2+) cations without greatly affecting the structure of the compound. The Mn and Cd cations were found to be randomly distributed over the A-site. Magnetization measurements indicated that the samples order antiferromagnetically at low temperature with a transition temperature that decreases with increasing Cd doping. The nuclear and magnetic structure of one specially prepared (114)Cd containing sample: Mn(1.5) (114)Cd(1.5)TeO(6), was studied using neutron powder diffraction over the temperature range 2-295 K. Mn(1.5) (114)Cd(1.5)TeO(6) was found to order in an incommensurate helical magnetic structure, very similar to that of Mn(3)TeO(6) [Ivanov et al., 2011 [3]]. However, with a lower transition temperature and the extension of the ordered structure confined to order 240(10) angstrom.
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| 9. |
- Ivanov, S. A., et al.
(författare)
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Structural and magnetic properties of the ordered perovskite Pb2CoTeO6
- 2010
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 39:46, s. 11136-11148
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Tidskriftsartikel (refereegranskat)abstract
- The complex perovskite Pb2CoTeO6 (PCTO) has been prepared as polycrystalline powders by a solid state reaction route, and the crystal structure and magnetic properties have been investigated using a combination of X-ray and neutron powder diffraction, electron microscopy, dielectric, calorimetric and magnetic measurements. It was shown that at room temperature this compound adopts a trigonal perovskite structure, space group R (3) over bar (a = 5.6782(1) angstrom, c = 13.8552(3) angstrom). The compound undergoes a number of temperature-induced phase transitions and adopts four different structures in the temperature range 5 500 K: monoclinic in P2(1)/n (5 < T < 125 K, tilt system (a(+)b(-)b(-))), monoclinic in I2/m (125 < T < 210 K, tilt system (a(0)b(-)b(-))), rhombohedral in R (3) over bar (210 < T < 370 K, tilt system (a(-)a(-)a(-))), and finally cubic in Fm (3) over barm (above 370 K without any tilting). These structural phase transitions are coupled to changes in the dielectric constant and the heat capacity around 210 and 370 K. A long-range antiferromagnetically ordered state has been identified from neutron powder diffraction and magnetic studies at different temperatures. Magnetic diffraction peaks were registered below the transition at about 16 K and a possible model for the magnetic structure is proposed. Possible coexistence of long-range ordering of the electrical dipoles and the magnetic moments at low temperatures making PCTO a potential multiferroic candidate is discussed.
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| 10. |
- Ivanov, Sergey A., et al.
(författare)
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Temperature-dependent multi-k magnetic structure in multiferroic Co3TeO6
- 2012
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Ingår i: Materials research bulletin. - : Elsevier BV. - 0025-5408 .- 1873-4227. ; 47:1, s. 63-72
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Tidskriftsartikel (refereegranskat)abstract
- A complex magnetic order of the multiferroic compound Co(3)TeO(6) has been revealed by neutron powder diffraction studies on ceramics and crushed single crystals. The compound adopts a monoclinic structure (s.g. C2/c) in the studied temperature range 2-300 K but exhibits successive antiferromagnetic transitions at low temperature. Incommensurate antiferromagnetic order with the propagation vector k(1) = (0, 0.485, 0.055) sets in at 26 K. A transition to a second antiferromagnetic structure with k(2) = (0, 0, 0) takes place at 21.1 K. Moreover, a transition to a commensurate antiferromagnetic structure with k(3) = (0, 0.5, 0.25) occurs at 17.4 K. The magnetic structures have been determined by neutron powder diffraction using group theory analysis as a preliminary tool. Different coordinations of the Co(2+) ions involved in the low-symmetry C2/c structure of Co(3)TeO(6) render the exchange-interaction network very complex by itself. The observed magnetic phase transformations are interpreted as an evidence of competing magnetic interactions. The temperature dependent changes in the magnetic structure, derived from refinements of high-resolution neutron data, are discussed and possible mechanisms connected with the spin reorientations are described.
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| 11. |
- Ivanov, Sergey, et al.
(författare)
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Short-Range Spin Order and Frustrated Magnetism in Mn(2)InSbO(6) and Mn(2)ScSbO(6)
- 2011
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Ingår i: European Journal of Inorganic Chemistry. - : Wiley. - 1434-1948 .- 1099-1948 .- 1099-0682. ; :30, s. 4691-4699
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Tidskriftsartikel (refereegranskat)abstract
- The complex metal oxides Mn(2)ASbO(6) (A = In, Sc) with a corundum-related structure A(3)BO(6) were prepared as polycrystalline powders by a solid-state reaction route. Their crystal structure and magnetic properties were investigated by using a combination of X-ray and neutron powder diffraction, electron microscopy, calorimetric, and magnetic measurements. At room temperature, these compounds adopt a trigonal structure, space group R (3) over bar, with a = 8.9313(1) angstrom, c = 10.7071(2) angstrom (for In) and a = 8.8836(1) angstrom, c = 10.6168(2) angstrom (for Sc), which persists down to 1.6 K. The Mn and A cations were found to be randomly distributed over the A sites. The overall behavior of the magnetization of Mn(2)InSbO(6) and that of Mn(2)ScSbO(6) are quite similar. In spite of the relatively large amount of Mn ions on the A site, only short-range magnetism is observed. Neutron diffraction patterns of Mn(2)InSbO(6) showed no evidence of a long-range magnetic ordering at 1.6 K, instead only a weak diffuse magnetic peak was observed at low temperatures. The factors governing the observed structural and magnetic properties of Mn(2)ASbO(6) are discussed and compared with those of other Mn-containing complex metal oxides with a corundum-related structure. The influence of the A cation sublattice on the magnetic properties is also considered.
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| 12. |
- Mathieu, Roland, et al.
(författare)
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Influence of the A cation on the low-temperature antiferromagnetism of ordered antiferroelectric A(2)CoTeO(6) perovskites
- 2011
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 83:17, s. 174420-
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the structural and magnetic properties of antiferroelectric A(2)CoTeO(6) perovskites with A = Cd, Ca, Sr, Pb, and Ba. All compounds are antiferromagnetic at low temperatures, with the antiferromagnetic transition temperature slightly decreasing with decreasing ionic size of the A cation. Such a decrease in antiferromagnetic interaction is not observed in A(2)(2+)CoM(6+)O(6) materials with other M6+ cations of similar ionic sizes, suggesting that Te6+ cations affect the electronic and in turn the magnetic structure of the system.
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| 13. |
- Akhter, Shahida, et al.
(författare)
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Magnetic and magnetocaloric properties of Cu1-xZnxFe2O4 (x=0.6, 0.7, 0.8) ferrites
- 2014
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 367, s. 75-80
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Tidskriftsartikel (refereegranskat)abstract
- The effect of Zn substitution on the magnetic and magnetocaloric properties of Cu1-xZnxFe2O4 (x=0.6, 0.7, 0.8) ferrites over a wide temperature range has been investigated. The polycrystalline samples were synthesized using the solid-state reaction at sintering temperature 1050 degrees C (1323 K) for 2 h and has been characterized by SQUID magnetometry. Magnetization versus temperature showed that all samples exhibit a paramagnetic to ferromagnetic transition with decreasing temperature. The Curie temperature T-c is found to decrease from 373 K for x=0.6 to 140 K for x=0.8 as well as the saturation magnetization Ms which shifts from 100 to 44 emu/gm. The magnetocaloric effect was obtained by measuring a family of M-I1 curves at set temperature intervals and calculating the entropy change, LIS for this system using the Maxwell relation. The AS of all samples increased with increasing applied field and showed a maximum around their respective 'Fe. The entropy change (Delta S) decreased with increasing Zn content, whereas the relative cooling power (RCP) slightly increased. The large RCP and Delta S found in Zn substitution Cu-Zn ferrites will be interesting for magnetic refrigeration near room temperature.
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| 14. |
- Andersson, Mikael Svante, et al.
(författare)
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Ageing dynamics of a superspin glass
- 2014
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Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 108:1, s. 17004-
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Tidskriftsartikel (refereegranskat)abstract
- Magnetization dynamics of a model superspin glass system consisting of nearly monodispersed close-packed maghemite particles of diameter 8 nm is investigated. The observed non-equilibrium features of the dynamics are qualitatively similar to those of atomic spin glass systems. The intrinsic relaxation function, as observed in zero-field-cooled magnetization relaxation experiments, depends on the time the sample has been kept at constant temperature (ageing). Accompanying low-field experiments show that the archetypal spin glass characteristics -ageing, memory and rejuvenation- are reproduced in this dense system of dipolar-dipolar interacting superspins.
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| 15. |
- Andersson, Mikael, et al.
(författare)
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Super spin dimensionality of a mono-dispersed and densely packed magnetic nanoparticle system
- 2014
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596.
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Konferensbidrag (refereegranskat)abstract
- The dynamics of a dense near mono-dispersed assembly of maghemite nanoparticles is investigated by measurements of the temperature dependence of the isothermal remnant magnetization induced by temporal application of weak magnetic fields at constant temperature. The results suggest that the dimensionality of the super spins of the particles is of Heisenberg character at high temperatures but crossover to become Ising like at lower temperatures.
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| 16. |
- Bandyopadhyay, Sulalit, et al.
(författare)
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Synthesis and in vitro cellular interactions of superparamagnetic iron nanoparticles with a crystalline gold shell
- 2014
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 316, s. 171-178
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Tidskriftsartikel (refereegranskat)abstract
- Fe@Au core-shell nanoparticles (NPs) exhibit multiple functionalities enabling their effective use in applications such as medical imaging and drug delivery. In this work, a novel synthetic method was developed and optimized for the synthesis of highly stable, monodisperse Fe@Au NPs of average diameter similar to 24 nm exhibiting magneto-plasmonic characteristics. Fe@Au NPs were characterized by a wide range of experimental techniques, including scanning (transmission) electron microscopy (S(T)EM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX), dynamic light scattering (DLS) and UV-vis spectroscopy. The formed particles comprise an amorphous iron core with a crystalline Au shell of tunable thickness, and retain the superparamagnetic properties at room temperature after formation of a crystalline Au shell. After surface modification, PEGylated Fe@Au NPs were used for in vitro studies on olfactory ensheathing cells (OECs) and human neural stem cells (hNSCs). No adverse effects of the Fe@Au particles were observed post-labeling, both cell types retaining normal morphology, viability, proliferation, and motility. It can be concluded that no appreciable toxic effects on both cell types, coupled with multifunctionality and chemical stability make them ideal candidates for therapeutic as well as diagnostic applications.
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| 17. |
- Boschker, J. E., et al.
(författare)
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In-plane structural order of domain engineered La0.7Sr0.3MnO3 thin films
- 2013
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Ingår i: Philosophical Magazine. - : Informa UK Limited. - 1478-6435 .- 1478-6443. ; 93:13, s. 1549-1562
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Tidskriftsartikel (refereegranskat)abstract
- We present a detailed structural study of tensile-strained La0.7Sr0.3MnO3 thin films. We use the substrate miscut to control the number of rhombohedral variants in the films and study the in-plane order and structural distortions. Using high-resolution X-ray diffraction, we demonstrate that step-edge induced lattice modulations occur in 4-variant films, whereas periodic twinning is the dominant in-plane order for 2-variant films. We show that the in-plane twinning angle is almost completely relaxed. However, the relaxation of shear strain by the out-of-plane twinning angle and the monoclinic distortion is only partial. Furthermore, the film thickness dependence of the domain width reveals that domain formation is a universal mechanism for shear strain relaxation. Finally, we show that the structural response to the transition from the paramagnetic to the ferromagnetic phase of La0.7Sr0.3MnO3 at 345K is smaller in 4-variant films compared to 2-variant films.
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| 18. |
- Brotin, Thierry, et al.
(författare)
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High Affinity of Water-Soluble Cryptophanes for Cesium Cations
- 2012
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 77:2, s. 1198-1201
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Tidskriftsartikel (refereegranskat)abstract
- Exceptionally high affinity for cesium cations was achieved in aqueous solution using two enantiopure cryptophanes. Complexation of cesium was evidenced by Cs-133 NMR spectroscopy and by electronic circular dichroism (ECD). Binding constants as high as 6 X 10(9) M-1 have been measured by isothermal titration calorimetry (ITC). Very strong complexation of rubidium cations (K similar to 10(6) M-1) has also been measured. Chiral hosts allowed the detection of the two cations at low concentrations (mu M) using ECD.
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| 19. |
- Choudhury, D., et al.
(författare)
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Near-Room-Temperature Colossal Magnetodielectricity and Multiglass Properties in Partially Disordered La2NiMnO6
- 2012
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 108:12, s. 127201-
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Tidskriftsartikel (refereegranskat)abstract
- We report magnetic, dielectric, and magnetodielectric responses of the pure monoclinic bulk phase of partially disordered La2NiMnO6, exhibiting a spectrum of unusual properties and establish that this compound is an intrinsically multiglass system with a large magnetodielectric coupling (8%-20%) over a wide range of temperatures (150-300 K). Specifically, our results establish a unique way to obtain colossal magnetodielectricity, independent of any striction effects, by engineering the asymmetric hopping contribution to the dielectric constant via the tuning of the relative-spin orientations between neighboring magnetic ions in a transition-metal oxide system. We discuss the role of antisite (Ni-Mn) disorder in emergence of these unusual properties.
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| 20. |
- Choudhury, Debraj, et al.
(författare)
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Tuning of dielectric properties and magnetism of SrTiO3 by site-specific doping of Mn
- 2011
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 84:12, s. 125124-
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Tidskriftsartikel (refereegranskat)abstract
- Combining experiments with first-principles calculations, we show that site-specific doping of Mn into SrTiO(3) has a decisive influence on the dielectric properties of these doped systems. We find that phonon contributions to the dielectric constant invariably decrease sharply on doping at any site. However, a sizable, random dipolar contribution only for Mn at the Sr site arises from a strong off-centric displacement of Mn in spite of Mn being in a non-d(0) state; this leads to a large dielectric constant at higher temperatures and gives rise to a relaxor ferroelectric behavior at lower temperatures. We also investigate magnetic properties in detail and critically reevaluate the possibility of a true multiglass state in such systems.
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| 21. |
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| 22. |
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| 23. |
- Hudl, Mattias, et al.
(författare)
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Complex magnetism and magnetic-field-driven electrical polarization of Co(3)TeO(6)
- 2011
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 84:18, s. 180404-
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Tidskriftsartikel (refereegranskat)abstract
- The magnetic and electrical properties of Co(3)TeO(6) single crystals with corundum-related structure reveal a magnetic-field-induced polarization below 21 K. A sharp peak in the specific heat at approximate to 18 K indicates a reconstructive-type first-order phase transition. From second-harmonic generation measurements, breaking of inversion symmetry is evident and the point-group symmetry was determined as m. The temperature and magnetic-field dependences of the magnetic and electrical polarizations are discussed in the light of the SHG results.
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| 24. |
- Hudl, Matthias, et al.
(författare)
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Investigation of the magnetic phase transition and magnetocaloric properties of the Mn2FeSbO6 ilmenite
- 2013
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 331, s. 193-197
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Tidskriftsartikel (refereegranskat)abstract
- The magnetic phase transition and magnetocaloric properties of both mineral and synthetic melanostibite Mn2FeSbO6 with ilmenite-type structure have been studied. Mn2FeSbO6 orders ferrimagnetically below 270 K and is found to undergo a second-order magnetic phase transition. The associated magnetic entropy change was found to be 1.7 J/kg K for the mineral and 1.8 J/kg K for the synthetic melanostibite for 5 T field change. For the synthetic Mn2FeSbO6 the adiabatic temperature change was estimated from magnetic- and specific heat measurements and amounts to 0.2 K in 1 T field change. Perspectives of the functional properties of Mn2FeSbO6-based materials are discussed.
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| 25. |
- Ivanov, Sergey A., et al.
(författare)
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Temperature evolution of structural and magnetic properties of stoichiometric LiCu2O2 : Correlation of thermal expansion coefficient and magnetic order
- 2014
-
Ingår i: Solid State Sciences. - : Elsevier BV. - 1293-2558 .- 1873-3085. ; 34, s. 97-101
-
Tidskriftsartikel (refereegranskat)abstract
- Temperature-dependent crystallographic and magnetic studies on stoichiometric single crystals of LiCu2O2 are reported. The temperature dependence of the lattice parameters was extracted from X-ray powder diffractograms collected on crushed single crystals, from 12 K to 295 K. The magnetic properties are similar to earlier findings demonstrating antiferromagnetic ordering below 25 K. Evidence of magnetoelastic coupling is observed in the thermal expansion along the c-direction; not only at the low temperature antiferromagnetic transitions, but an anomalous behavior of the thermal expansion indicate magnetoelastic coupling also to the magnetic ordering related to a weak spontaneous magnetic moment appearing at 150 K. Ac-susceptibility measurements at different frequencies and superposed dc-fields are employed to further characterize this magnetic anomaly.
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| 26. |
- Kaleva, G M, et al.
(författare)
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Phase Transitions of (Cu,Ni)(3)TeO(6) Solid Solutions
- 2011
-
Ingår i: Inorganic Materials (Neorganicheskie materialy). - 0020-1685 .- 1608-3172. ; 47:10, s. 1132-1140
-
Tidskriftsartikel (refereegranskat)abstract
- (Cu,Ni)(3)TeO(6) solid solutions with the bixbyite (pseudocorundum) and ilmenite structures have been prepared by solid-state reactions and characterized by a variety of techniques. We have studied the effect of nickel substitution for copper on the phase composition of the materials, examined the microstructure of ceramic samples, and measured their magnetic susceptibility, heat capacity, permittivity, and loss tangent as functions of temperature. This allowed us to reveal dielectric anomalies related to structural phase transitions and to determine the antiferromagnetic ordering temperatures of the (Cu,Ni)(3)TeO(6) ceramics.
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| 27. |
- Kaleva, G. M., et al.
(författare)
-
Preparation, electrical conductivity, and magnetic susceptibility of (Ba1-x Bi (x) )(Mn0.5+x/2Nb0.5-x/2)O-3
- 2013
-
Ingår i: Inorganic Materials (Neorganicheskie materialy). - 0020-1685 .- 1608-3172. ; 49:5, s. 513-516
-
Tidskriftsartikel (refereegranskat)abstract
- (Ba1 - x Bi (x) )(Mn0.5 + x/2Nb0.5 - x/2)O-3 perovskite solid solutions have been prepared by solid-state reactions and their physicochemical properties have been investigated. We have studied the influence of bismuth substitution for barium cations on the phase composition of the samples. Their magnetic susceptibility and electrical conductivity have been measured as functions of temperature. The composition dependence of the antiferromagnetic ordering temperature is presented.
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| 28. |
- Kamentsev, K. E., et al.
(författare)
-
High-temperature structural phase transition in the LiCu2O2 multiferroic
- 2013
-
Ingår i: Journal of Experimental and Theoretical Physics. - 1063-7761 .- 1090-6509. ; 117:2, s. 320-326
-
Tidskriftsartikel (refereegranskat)abstract
- The results of thermogravimetric, X-ray diffraction, and electrical studies of LiCu2O2 single crystals in the temperature range 300-1100 K are presented. A reversible first-order phase transition between the orthorhombic and tetragonal phases is found to occur in these single crystals at T = 993 K. A pronounced peak on a differential thermal analysis curve and jumps in the unit cell parameters and the electrical resistivity are detected at the phase-transition temperature. The data on the crystal structure of LiCu2O2 and the phase transition-induced change in the entropy determined in this work are used to conclude that the revealed phase transition is caused by the ordering-disordering of Li+ and Cu2+ cations in their structural positions.
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| 29. |
- Kovacs, A., et al.
(författare)
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Voids and Mn-rich inclusions in a (Ga,Mn)As ferromagnetic semiconductor investigated by transmission electron microscopy
- 2011
-
Ingår i: Applied Physics Reviews. - : AIP Publishing. - 1931-9401. ; 109:8, s. 1-083546
-
Tidskriftsartikel (refereegranskat)abstract
- Voids adjacent to cubic (ZnS-type) and hexagonal (NiAs-type) Mn-rich nanocrystals are characterized using aberration-corrected transmission electron microscopy in an annealed Ga(0.995)Mn(0.005)As magnetic semiconductor specimen grown by molecular beam epitaxy. Nanobeam electron diffraction measurements suggest that the nanocrystals exhibit deviations in lattice parameter as compared to bulk MnAs. After annealing at 903 K, the magnetic transition temperature of the specimen is likely to be dominated by the presence of cubic ferromagnetic nanocrystals. In situ annealing inside the electron microscope is used to study the nucleation, coalescence, and grain growth of individual nanocrystals.
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| 30. |
- Kumar, P. Anil, et al.
(författare)
-
Ferrimagnetism, antiferromagnetism, and magnetic frustration in La2-xSrxCuRuO6 (0 <= x <= 1)
- 2012
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : APS. - 1098-0121 .- 1550-235X. ; 86:9, s. 094421-
-
Tidskriftsartikel (refereegranskat)abstract
- We studied structural and magnetic properties of a series of insulating double perovskite compounds, La2-xSrxCuRuO6 (0 <= x <= 1), representing doping via A-site substitution. The end members La2CuRuO6 and LaSrCuRuO6 form in monoclinic structure while the intermediate Sr doped compounds stabilize in triclinic structure. The Cu and Ru ions sit on alternate B sites of the perovskite lattice with similar to 15% antisite defects in the undoped sample while the Sr-doped samples show a tendency to higher ordering at B sites. The undoped (x = 0) compound shows a ferrimagnetic-like behavior at low temperatures. In surprising contrast to the usual expectation of an enhancement of ferromagnetic interaction on doping, an antiferromagnetic-like ground state is realized for all doped samples (x > 0). Heat capacity measurements indicate the absence of any long-range magnetic order in any of these compounds. The magnetic relaxation and memory effects observed in all compounds suggest glassy dynamical properties associated with magnetic disorder and frustration. We show that the observed magnetic properties are dominated by the competition between the nearest-neighbor Ru-O-Cu 180 degrees superexchange interaction and the next-nearest-neighbor Ru-O-O-Ru 90 degrees superexchange interaction as well as by the formation of antisite defects with interchanged Cu and Ru positions. Our calculated exchange interaction parameters from first principles calculations for x = 0 and x = 1 support this interpretation.
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| 31. |
- Kumar, P. Anil, et al.
(författare)
-
Superspin glass state and exchange bias in amorphous Fe/Fe-O core/shell nanoparticles
- 2014
-
Ingår i: Materials Research Express. - : IOP Publishing. - 2053-1591. ; 1:3
-
Tidskriftsartikel (refereegranskat)abstract
- Nanoparticles of iron and iron oxide are widely explored in several biomedical and technological applications. We report on the magnetic properties of amorphous Fe/Fe-O core/shell nanoparticles compared to those of a reference system with crystalline Fe-O nanoparticles. These nanoparticles are prepared by thermal decomposition of iron precursor, where the amorphous and crystalline nature of core and shell is determined by the choice and concentration of the ligand. The crystalline system exhibits a blocking temperature higher than 300K and negligible exchange bias effect. In contrast, the amorphous systems display large exchange bias, and collective magnetic behavior at low temperatures, with features of magnetic frustration and disorder reminiscent of those observed in spin glass and superspin glass systems. We discuss the origin of the dynamical magnetic behavior of the amorphous particles and study the dependence of the exchange bias field on the cooling field.
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| 32. |
- Kumar Puri, Anil, et al.
(författare)
-
Reentrant Superspin Glass Phase in a La0.82Ca0.18MnO3 Ferromagnetic Insulator
- 2014
-
Ingår i: Physical Review X. - 2160-3308. ; 4:1, s. 011037-
-
Tidskriftsartikel (refereegranskat)abstract
- We report results of the magnetization and ac susceptibility measurements down to very low fields on a single crystal of the perovskite manganite, La-0.82 Ca-0.18 MnO3. This composition falls in the intriguing ferromagnetic insulator region of the manganite phase diagram. In contrast to earlier beliefs, our investigations reveal that magnetically (and in every other sense), this is a single- phase system with a ferromagnetic ordering temperature of around 170 K. However, this ferromagnetic state is magnetically frustrated, and the system exhibits pronounced glassy dynamics below 90 K. Based on measured dynamical properties, we propose that this quasi-long-ranged ferromagnetic phase, and the associated superspin glass behavior, is the true magnetic state of the system, rather than being a macroscopic mixture of ferromagnetic and antiferromagnetic phases, as often suggested. Our results provide an understanding of the quantum phase transition from an antiferromagnetic insulator to a ferromagnetic metal via this ferromagnetic state as a function of x in La1-xCaxMnO3, in terms of the possible formation of magnetic polarons.
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| 33. |
- Lagrange, Mathieu, et al.
(författare)
-
Explicit modeling of temporal dynamics within musical signals for acoustical unit similarity
- 2010
-
Ingår i: PATTERN RECOGNITION LETTERS. - : Elsevier Science B.V., Amsterdam.. - 0167-8655. ; 31:12, s. 1498-1506
-
Tidskriftsartikel (refereegranskat)abstract
- Timbre is a major cue for the human auditory system to recognize musical sounds. To describe timbre, the temporal dynamics is an important component as well as the widely used spectral envelope. In this paper, we present new temporal dynamics similarity measures, which will prove valuable for the recognition of timbral patterns. These similarity measures are evaluated, first alone, then in conjunction with spectral envelope similarity measures, for both single tones and solo recordings. Results are provided, showing that the new temporal dynamics features significantly improve timbral pattern recognition.
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| 34. |
- Mathieu, Roland, et al.
(författare)
-
Dynamical studies on model spin glasses
- 2010
-
Ingår i: International Conference on Magnetism (ICM 2009). - : IOP Publishing. ; , s. 032042-
-
Konferensbidrag (refereegranskat)abstract
- The dynamical magnetic properties of a Cu(Mn) Heisenberg spin glass have been investigated by SQUID magnetometry. The zero-field-cooled magnetization has been recorded as a function of the temperature and time after specific cooling protocols, in order to study in detail the so-called memory effect displayed by spin-glasses.
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| 35. |
- Mathieu, Roland, et al.
(författare)
-
Enhancement of antiferromagnetic interaction and transition temperature in M3TeO6 systems (M = Mn, Co, Ni, Cu)
- 2013
-
Ingår i: European Physical Journal B. - : Springer Science and Business Media LLC. - 1434-6028 .- 1434-6036. ; 86:8, s. 361-
-
Tidskriftsartikel (refereegranskat)abstract
- Several M3TeO6 (M = Mn, Co, Ni, Cu) oxides order antiferromagnetically at low temperatures (less than or similar to 60 K), while displaying interesting dielectric properties at high temperatures (ferroelectricity below 1000 K in M = Ni case). We have investigated and analyzed the structural and magnetic properties of Mn-doped Co3TeO6 and Ni3TeO6, which order antiferromagnetically at temperatures higher than their undoped counterparts.
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| 36. |
- Mathieu, Roland, et al.
(författare)
-
Isothermal remanent magnetization and the spin dimensionality of spin glasses
- 2010
-
Ingår i: Philosophical Magazine Letters. - : Informa UK Limited. - 0950-0839 .- 1362-3036. ; 90:10, s. 723-729
-
Tidskriftsartikel (refereegranskat)abstract
- The isothermal remanent magnetization is used to investigate dynamical magnetic properties of spatially three-dimensional spin glasses with different spin dimensionality (Ising, XY, Heisenberg). The isothermal remanent magnetization is recorded versus temperature after the application of a weak magnetic field at a constant temperature T-h. We observe that in the case of the Heisenberg spin glasses, the equilibrated spin structure and the direction of the excess moment are recovered at T-h. The isothermal remanent magnetization thus reflects the directional character of the Dzyaloshinsky-Moriya interaction present in Heisenberg systems.
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| 37. |
- Mathieu, Roland, et al.
(författare)
-
Magnetic order near 270 K in mineral and synthetic Mn2FeSbO6 ilmenite
- 2011
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 98:20, s. 202505-1-202505-3
-
Tidskriftsartikel (refereegranskat)abstract
- The structural and magnetic properties of Mn2FeSbO6 single-crystalline mineral and ceramic samples synthesized under thermobaric treatment have been investigated, and compared to theoretical predictions based on first-principles electronic structure calculations. This ilmenite system displays a sharp magnetic transition just below the room temperature related to a ferrimagnetic ordering of the Mn2+ and Fe3+ cations, which makes Mn2FeSbO6 a promising candidate for designing functional magnetic materials.
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| 38. |
- Mathieu, Roland, et al.
(författare)
-
Memory and rejuvenation in a spin glass
- 2010
-
Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 90:6, s. 67003-
-
Tidskriftsartikel (refereegranskat)abstract
- The temperature dependence of the magnetisation of a Cu(Mn) spin glass (T-g approximate to 57 K) has been investigated using weak probing magnetic fields (H = 0.5 or 0 Oe) and specific thermal protocols. The behaviour of the zero-field-cooled, thermoremanent and isothermal remanent magnetisation on (re-) cooling the system from a temperature (40K) where the system has been aged is investigated. It is observed that the measured magnetisation is formed by two parts: i) a temperature- and observation time-dependent thermally activated relaxational part governed by the age- and temperature-dependent response function and the (latest) field change made at a lower temperature, superposed on ii) a weakly temperature-dependent frozen-in part. Interestingly we observe that the spin configuration that is imprinted during an elongated halt in the cooling, if it is accompanied by a field-induced magnetisation, also includes a unidirectional excess magnetisation that is recovered on returning to the ageing temperature.
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| 39. |
- Mathieu, Roland, et al.
(författare)
-
Mn2FeSbO6 : A ferrimagnetic ilmenite and an antiferromagnetic perovskite
- 2013
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 87:1, s. 014408-
-
Tidskriftsartikel (refereegranskat)abstract
- Due to its polymorphism, Mn2FeSbO6 can be synthesized at high pressures and temperatures as a ferrimagnetic ilmenite or an antiferromagnetic perovskite. The structural phase transformation is discussed in detail, and magnetic structures are proposed for both phases. The high-pressure Mn2FeSbO6 polymorph is a rare example of A(2)B'B '' O-6 perovskite with solely Mn cations on the A site. Fe and Sb cations are ordered on the B sites. Theoretical calculations for the perovskite phase suggest a complex magnetic structure, holding an electronic polarization.
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| 40. |
- Mathieu, Roland, et al.
(författare)
-
Phase transition in a super superspin glass
- 2013
-
Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 102:6, s. 67002-
-
Tidskriftsartikel (refereegranskat)abstract
- We here confirm the occurrence of spin glass phase transition and extract estimates of associated critical exponents of a highly monodisperse and densely compacted system of bare maghemite nanoparticles. This system has earlier been found to behave like an archetypal spin glass, with, e.g., a sharp transition from paramagnetic to non-equilibrium behavior, suggesting that this system undergoes a spin glass phase transition at a relatively high temperature, T-g similar to 140K.
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| 41. |
- Monsen, Asmund, et al.
(författare)
-
Thickness dependence of dynamic and static magnetic properties of pulsed laser deposited La0.7Sr0.3MnO3 films on SrTiO3(001)
- 2014
-
Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 369, s. 197-204
-
Tidskriftsartikel (refereegranskat)abstract
- We present a comprehensive study of the thickness dependence of static and magneto-dynamic magnetic properties of La0.7Sr0.3MnO3. Epitaxial pulsed laser deposited La0.7Sr0.3MnO3 (001) thin films in the range from 3 unit cell (uc) to 40 uc (1.2-16 nm) have been investigated through ferromagnetic resonance (FMR) spectroscopy and SQUID magnetometry at variable temperature. Magnetodynamically, three different thickness, d, regimes are identified: 20 uc less than or similar to d uc where the system is bulk like, a transition region 8 uc < d less than or similar to 20 uc where the FMR linewidth and the position depend on thickness and d=6 uc which displays significantly altered magnetodynamic properties, while still displaying bulk magnetization. Magnetization and FMR measurements are consistent with a nonmagnetic volume corresponding to similar to 4 uc. We observe a reduction of Curie temperature (T-c) with decreasing thickness, which is coherent with a mean field model description. The reduced ordering temperature also accounts for the thickness dependence of the magnetic anisotropy constants and resonance fields. The clamping of the system is strongly thickness dependent, and is for thin films dominated by thickness dependent anisotropies, yielding both a strong two-magnon scattering close to T-c and a low temperature broadening. For the bulk like samples a large part of the broadening can be linked to spread in magnetic anisotropies attributed to crystal imperfections/domain boundaries of the bulk like film.
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| 42. |
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| 43. |
- Norberg, Stefan, 1972, et al.
(författare)
-
Local structural properties of 0.5BiMnO(3)-0.5ATiO(3) (A = Ba or Sr)
- 2010
-
Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1359-7345 .- 1364-548X. ; 46:9, s. 1455-1457
-
Tidskriftsartikel (refereegranskat)abstract
- Neutron total scattering data have been used to probe the long-and short-range structure of 0.5BiMnO(3)-0.5ATiO(3) (A = Ba or Sr). Modelling of the total scattering data, using the reverse Monte Carlo (RMC) method, reveals local disorder that differs substantially from the average structure. Significantly, the Bi3+ cations prefer to adopt an asymmetric coordination due to the influence of the lone-pair electrons.
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| 44. |
- Sadowski, Janusz, et al.
(författare)
-
Formation of two-dimensionally confined superparamagnetic (Mn, Ga)As nanocrystals in high-temperature annealed (Ga, Mn)As/GaAs superlattices
- 2013
-
Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 25:19, s. 6-196005
-
Tidskriftsartikel (refereegranskat)abstract
- The annealing-induced formation of (Mn, Ga)As nanocrystals in (Ga, Mn)As/GaAs superlattices was studied by x-ray diffraction, transmission electron microscopy and magnetometry. The superlattice structures with 50 Å thick (Ga, Mn)As layers separated by 25, 50 and 100 Å thick GaAs spacers were grown by molecular beam epitaxy at low temperature (250 ° C), and then annealed at high temperatures of 400, 560 and 630 ° C. The high-temperature annealing causes decomposition to a (Ga, Mn)As ternary alloy and the formation of (Mn, Ga)As nanocrystals inside the GaAs matrix. The nanocrystals are confined in the planes that were formerly occupied by (Ga, Mn)As layers for the up to 560 ° C annealing and diffuse throughout the GaAs spacer layers at 630 ° C annealing. The two-dimensionally confined nanocrystals exhibit a superparamagnetic behavior which becomes high-temperature ferromagnetism (~350 K) upon diffusion.
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| 45. |
- Sadowski, Janusz, et al.
(författare)
-
Formation process and superparamagnetic properties of (Mn,Ga)As nanocrystals in GaAs fabricated by annealing of (Ga,Mn)As layers with low Mn content
- 2011
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 84:24, s. 245306-
-
Tidskriftsartikel (refereegranskat)abstract
- X-ray diffraction, transmission electron microscopy, and magnetization measurements are employed to study the structural and magnetic properties of Mn-rich (Mn,Ga)As nanocrystals embedded in GaAs. These nanocomposites are obtained by moderate-temperature (400 degrees C) and high-temperature (560 degrees C and 630 degrees C) annealing of (Ga,Mn)As layers with Mn concentrations between 0.1% and 2%, grown by molecular beam epitaxy at 270 degrees C. Decomposition of (Ga,Mn)As is already observed at the lowest annealing temperature of 400 degrees C for layers with initial Mn content of 1% and 2%. Both cubic and hexagonal (Mn, Ga) As nanocrystals, with similar diameters of 7-10 nm, are observed to coexist in layers with an initial Mn content of 0.5% and 2% after higher-temperature annealing. Measurements of magnetization relaxation in the time span 0.1-10 000 s provide evidence for superparamagnetic properties of the (Mn,Ga)As nanocrystals, as well as for the absence of spin-glass dynamics. These findings point to weak coupling between nanocrystals even in layers with the highest nanocrystal density.
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| 46. |
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| 47. |
- Vasilakaki, M., et al.
(författare)
-
Memory effects on the magnetic behavior of assemblies of nanoparticles with ferromagnetic core/antiferromagnetic shell morphology
- 2013
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 88:14, s. 140402-
-
Tidskriftsartikel (refereegranskat)abstract
- Monte Carlo simulations of the dynamic magnetic behavior of an assembly of ferromagnetic core/antiferromagnetic shell nanoparticles are reported and compared with the experimental results on a system of Co nanoparticles in Mn matrix. Memory effects on low-field zero-field-cooled magnetization curves have been investigated. Our simulations show that the memory effects increase with the concentration and that both the interface exchange coupling and the dipolar interparticle interactions contribute to the observed dynamic behavior. In particular the interface exchange interaction provides an additive source for the frustration of the system resulting in an enhancement of the memory effect. The numerical data reproduce well the experimental results confirming the glassy behavior of the investigated nanoparticle systems.
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| 48. |
- Weil, M., et al.
(författare)
-
Crystal growth experiments in the systems Ni2MSbO6 (M = Sc, In) using chemical vapour transport reactions : Ni2InSbO6 and NiSb2O6 crystals in the millimetre range
- 2014
-
Ingår i: Crystal research and technology (1981). - : Wiley. - 0232-1300 .- 1521-4079. ; 49:2-3, s. 142-151
-
Tidskriftsartikel (refereegranskat)abstract
- Endothermic chemical vapour transport (CVT) reactions of Ni2MSbO6 (M = Sc, In), using a temperature gradient (T) over bar of 1313 -> 1233 K and HgCl2, HgBr2, PtCl2 or TeCl4 as transport agents, led to growth of Ni2InSbO6 single crystals in the millimetre range, whereas in the case of Ni2ScSbO6 an incongruent dissolution of the solid in the source region was observed, leading to the formation of single crystals of the ternary phase NiSb2O6 in the sink region. The crystal structures of the obtained crystals were refined from single crystal X-ray data with high precision [Ni2InSbO6: R3, Z = 3, a = 5.21640(10) angstrom, c = 14.0142(3) angstrom, 1279 structure factors, 33 parameters, R[F-2 > 2 sigma(F-2)] = 0.0189; NiSb2O6: P4(2)/mnm, Z = 2, a = 4.63910(10) angstrom, c = 9.2182(2) angstrom, 500 structure factors, 19 parameters, R[F-2 > 2 sigma(F-2)] = 0.0145]. Ni2InSbO6 crystallizes in a corundum-related structure, NiSb2O6 in the trirutile structure type. Spontaneous polarization and the ferroelectric transition temperature were estimated from the atomic arrangement and cation displacement along the polar axis in Ni2InSbO6. Magnetic measurements on Ni2InSbO6 evidence an antiferromagnetic transition near T-N = 74 K, with significant magnetic frustration.
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