| 1. |
- Hudl, Matthias, et al.
(författare)
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Nonlinear Magnetization Dynamics Driven by Strong Terahertz Fields
- 2019
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Ingår i: Physical Review Letters. - : AMER PHYSICAL SOC. - 0031-9007 .- 1079-7114. ; 123:19
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Tidskriftsartikel (refereegranskat)abstract
- We present a comprehensive experimental and numerical study of magnetization dynamics in a thin metallic film triggered by single-cycle terahertz pulses of ∼20 MV/m electric field amplitude and ∼1 ps duration. The experimental dynamics is probed using the femtosecond magneto-optical Kerr effect, and it is reproduced numerically using macrospin simulations. The magnetization dynamics can be decomposed in three distinct processes: a coherent precession of the magnetization around the terahertz magnetic field, an ultrafast demagnetization that suddenly changes the anisotropy of the film, and a uniform precession around the equilibrium effective field that is relaxed on the nanosecond time scale, consistent with a Gilbert damping process. Macrospin simulations quantitatively reproduce the observed dynamics, and allow us to predict that novel nonlinear magnetization dynamics regimes can be attained with existing tabletop terahertz sources.
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| 2. |
- Pancaldi, Matteo, et al.
(författare)
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Anti-reflection coating design for metallic terahertz meta-materials
- 2018
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Ingår i: Optics Express. - 1094-4087. ; 26:3, s. 2917-2927
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate a silicon-based, single-layer anti-reflection coating that suppresses the reflectivity of metals at near-infrared frequencies, enabling optical probing of nano-scale structures embedded in highly reflective surroundings. Our design does not affect the interaction of terahertz radiation with metallic structures that can be used to achieve terahertz near-field enhancement. We have verified the functionality of the design by calculating and measuring the reflectivity of both infrared and terahertz radiation from a silicon/gold double layer as a function of the silicon thickness. We have also fabricated the unit cell of a terahertz meta-material, a dipole antenna comprising two 20-nm thick extended gold plates separated by a 2 mu m gap, where the terahertz field is locally enhanced. We used the time-domain finite element method to demonstrate that such near-field enhancement is preserved in the presence of the anti-reflection coating. Finally, we performed magneto-optical Kerr effect measurements on a single 3-nm thick, 1-mu m wide magnetic wire placed in the gap of such a dipole antenna. The wire only occupies 2% of the area probed by the laser beam, but its magneto-optical response can be clearly detected. Our design paves the way for ultrafast time-resolved studies, using table-top femtosecond near-infrared lasers, of dynamics in nano-structures driven by strong terahertz radiation.
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| 3. |
- 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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| 4. |
- Bran, Cristina, et al.
(författare)
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Magnetic Properties of Fe/WRe (001) Multilayers
- 2014
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Ingår i: Journal of Surfaces and Interfaces of Materials. - : American Scientific Publishers. - 2164-7542. ; 2:1, s. 33-39
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Tidskriftsartikel (refereegranskat)abstract
- Following recent theoretical predictions on perpendicular uniaxial magnetocrystalline anisotropy in multilayers of 5 monolayers of Fe and 2 monolayers of W x Re100–x with tetragonally strained components, we have measured the magnetization and detailed atomic structure in a series of such samples with x = 20–80 at%. Although the achieved strain in the WRe layers is smaller than in the modelled case, we do observe a positive uniaxial magnetocrystalline anisotropy of around 0.6 MJ/m3 at 40 K, after accounting for the in-plane shape anisotropy. This causes the out-of-plane saturation field to be reduced considerably compared to a pure Fe thin film, while the saturation magnetization is maintained at a value which is enhanced by at least 30% from what would be expected from the multilayer composition alone. The coercivity is low, on the order of 6 kA/m in all samples.
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| 5. |
- 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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| 6. |
- Hudl, Matthias, 1981-
(författare)
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Magnetic materials with tunable thermal, electrical, and dynamic properties : An experimental study of magnetocaloric, multiferroic, and spin-glass materials
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis concerns and combines the results of experimental studies of magnetocaloric, multiferroic and spin-glass materials, using SQUID magnetometry as the main characteriza-tion technique. The magnetocaloric effect offers an interesting new technology for cooling and heating applications. The studies of magnetocaloric materials in this thesis are focused on experimen-tal characterization of fundamental magnetic properties of Fe2P-based materials. These are promising magnetocaloric materials with potential industrial use. It is found that the magneto-caloric properties of Fe2P can be optimally tuned by substitution of manganese for iron and silicon for phosphorus. Furthermore, a simple device to measure the magnetocaloric effect in terms of the adiabatic temperature change was constructed. Materials that simultaneously exhibit different types of ferroic order, for example magnetic and electrical order, are rare in nature. Among these multiferroic materials, those in which the ferroelectricity is magnetically-induced, or vice versa the magnetism is electrically-induced, are intensively studied due to a need for new functionalities in future data storage and logic devices. This thesis presents results on two materials: Co3TeO6 and Ba3NbFe3Si2O14, which belong to the group of magnetically-induced ferroelectrics and exhibit strong coupling be-tween the magnetic and the electrical order parameter. Their ordering properties were studied using magnetic and electrical measurement techniques. The coupling between the magnetic and electronic degrees of freedom was investigated using high-field and low-temperature Raman spectroscopy. Spin-glass materials exhibit complex magnetism and disorder. The influence of the spin dimensionality on the low and high magnetic field properties of spin glasses was investigated by studying model Heisenberg, XY and Ising spin-glass systems. Significant differences were found between the non-equilibrium dynamics and the hysteresis behavior of Heisenberg systems compared to those of XY and Ising spin glasses.
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| 7. |
- Hudl, Matthias, et al.
(författare)
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Order–disorder induced magnetic structures of FeMnP0.75Si0.25
- 2011
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 83:13, s. 134420-
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Tidskriftsartikel (refereegranskat)abstract
- We report on the synthesis and structural characterization of the magnetocaloric FeMnP0.75Si0.25 compound. Two types of samples (as quenched and annealed) were synthesized and characterized structurally and magnetically. We have found that minute changes in the degree of crystallographic order causes a large change in the magnetic properties. The annealed sample, with higher degree of order is antiferromagnetic with a zero net moment. The as-quenched sample has a net moment of 1.26 μB /f.u. and ferrimagnetic-like behavior. Theoretical calculations give rather large values for the Fe and Mn magnetic moments, both when occupied on the tetrahedral and pyramidal lattice site. The largest being the Mn moment for the pyramidal site reaches values as high as 2.8 μB /atom.
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| 8. |
- Hudl, Matthias, et al.
(författare)
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PPMS-based set-up for Raman and luminescence spectroscopy at high magnetic field, high pressure and low temperature
- 2015
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Ingår i: EPJ Techniques and Instrumentation. - : Springer Science and Business Media LLC. - 2195-7045. ; 2:1
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Tidskriftsartikel (refereegranskat)abstract
- We present an experimental set-up permitting Raman and luminescence spectroscopy studies in a commercial Physical Properties Measurement System (PPMS) from Quantum Design. Using this experimental set-up, gaseous, liquid and solid materials, in bulk or thin film form, may be investigated. The set-up is particularly suitable for the study of the spin-lattice coupling in strongly correlated oxide materials utilizing several different stimuli, e.g. magnetic and electric fields, high pressure and low temperatures. Details for the Raman extension, sample holder assembly and optical design, as well as data acquisition and measurement routine are described. Finally, we present exemplary results collected using the set-up, measured on reference materials, as well as on a correlated transition metal oxide.
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| 9. |
- Hudl, Matthias, et al.
(författare)
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Strongly enhanced magnetic moments in ferromagnetic FeMnP0.5Si0.5
- 2011
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 99:15, s. 152502-
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Tidskriftsartikel (refereegranskat)abstract
- The compound FeMnP(0.5)Si(0.5) has been studied by magnetic measurements, Mossbauer spectroscopy, and electronic structure and total energy calculations. An unexpectedly high magnetic hyperfine field for Fe atoms located at the tetrahedral Me(1) site in the Fe(2)P structure is found, The saturation moment derived from magnetic measurements corresponds to 4.4 mu(B)/f.u. at low temperatures, a value substantially higher than previously reported, but in accordance with the results from our electron structure calculations, This high saturation moment and the tunable first order ferromagnetic transition make the Fe(2-x)Mn(x)P(1-y)Si(y), system promising for magnetocaloric applications.
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| 10. |
- Hudl, Matthias, et al.
(författare)
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Thermodynamics around the first-order ferromagnetic phase transition of Fe2P single crystals
- 2014
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 90:14, s. 144432-
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Tidskriftsartikel (refereegranskat)abstract
- The specific heat and thermodynamics of Fe2P single crystals around the first-order paramagnetic to ferromagnetic (FM) phase transition at T-C similar or equal to 217 K are empirically investigated. The magnitude and direction of the magnetic field relative to the crystal axes govern the derived H-T phase diagram. Strikingly different phase contours are obtained for fields applied parallel and perpendicular to the c axis of the crystal. In parallel fields, the FM state is stabilized, while in perpendicular fields the phase transition is split into two sections, with an intermediate FM phase where there is no spontaneous magnetization along the c axis. The zero-field transition displays a textbook example of a first-order transition with different phase stability limits on heating and cooling. The results have special significance since Fe2P is the parent material to a family of compounds with outstanding magnetocaloric properties.
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| 11. |
- Hudl, Matthias, et al.
(författare)
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Tunable exchange bias in dilute magnetic alloys - chiral spin glasses
- 2016
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 6
-
Tidskriftsartikel (refereegranskat)abstract
- A unidirectional anisotropy appears in field cooled samples of dilute magnetic alloys at temperatures well below the cusp temperature of the zero field cooled magnetization curve. Magnetization measurements on a Cu(13.5 at% Mn) sample show that this anisotropy is essentially temperature independent and acts on a temperature dependent excess magnetization, Delta M. The anisotropy can be partially or fully transferred from being locked to the direction of the cooling field at lower fields to becoming locked to the direction of Delta M at larger fields, thus instead appearing as a uniaxial anisotropy. This introduces a deceiving division of the anisotropy into a superposition of a unidirectional and a uniaxial part. This two faced nature of the anisotropy has been empirically scrutinized and concluded to originate from one and the same exchange mechanism: the Dzyaloshinsky-Moriya interaction.
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| 12. |
- Höglin, Viktor, et al.
(författare)
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Detailed study of the magnetic ordering in FeMnP0.75Si0.25
- 2015
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Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 221, s. 240-246
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic and crystallographic properties of FeMnP0.75Si0.25 in the hexagonal Fe2P-type structure have been investigated by X-ray powder diffraction, neutron powder diffraction and magnetic measurements. The room temperature diffractograms reveal co-existence of two distinct structural phases in the samples with small, but significant, differences only in the unit cell dimensions. The volume ratio between the two phases is governed by the annealing conditions. One of the phases orders ferromagnetically (TC = 250 K) and the other in an incommensurate antiferromagnetic structure at low temperatures (qx = 0.363(1), TN = 150 K).
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| 13. |
- Höglin, Viktor, et al.
(författare)
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Phase diagram, structures and magnetism of the FeMnP1-xSix-system
- 2015
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 5:11, s. 8278-8284
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Tidskriftsartikel (refereegranskat)abstract
- The magnetic properties of the (Fe,Mn)(2)(P,Si)-system have been shown to be readily manipulated by small changes in composition. This study surveys the FeMnP1-xSix-system (0.00 <= x <= 1.00) reporting sample syntheses and investigations of crystallographic and magnetic properties using X-ray powder diffraction and magnetic measurements. Two single phase regions exist: the orthorhombic Co2P-type structure (x < 0.15) and the Fe2P-type structure (0.24 <= x < 0.50). Certain compositions have potential for use in magnetocaloric applications.
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| 14. |
- Höglin, Viktor, et al.
(författare)
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Phase diagram, structures and magnetism of the FeMnP1-xSix-system
- 2015
-
Ingår i: RSC Advances. - 2046-2069. ; 5:11, s. 8278-8284
-
Tidskriftsartikel (refereegranskat)abstract
- The magnetic properties of the (Fe,Mn)2(P,Si)-system have been shown to be readily manipulated by small changes in composition. This study surveys the FeMnP1−xSix-system (0.00 ≤ x ≤ 1.00) reporting sample syntheses and investigations of crystallographic and magnetic properties using X-ray powder diffraction and magnetic measurements. Two single phase regions exist: the orthorhombic Co2P-type structure (x < 0.15) and the Fe2P-type structure (0.24 ≤ x < 0.50). Certain compositions have potential for use in magnetocaloric applications.
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| 15. |
- Höglin, Viktor, et al.
(författare)
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The crystal and magnetic structure of the magnetocaloric compound FeMnP0.5Si0.5
- 2011
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Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 184:9, s. 2434-2438
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Tidskriftsartikel (refereegranskat)abstract
- The crystal and magnetic structure of the magnetocaloric compound FeMnP0.5Si0.5 has been studied by means of neutron and X-ray powder diffraction. Single phase samples of nominal composition FeMnP0.5Si0.5 have been prepared by the drop synthesis method. The compound crystallizes in the Fe2P-type structure (P-62m) with the magnetic moments aligned along the a-axis. It is found that the Fe atoms are mainly situated in the tetrahedral 3g site while the Mn atoms prefer the pyramidal 3f position. The material is ferromagnetic (TC=382 K) and at 296 K the total magnetic moment is 4.4 µB/f.u. It is shown that the magnetic moment in the 3f site is larger (2.5 µB) than in the 3g site (1.9 µB).
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| 16. |
- Ivanov, Sergey A., et al.
(författare)
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Spin and dipole order in geometrically frustrated mixed-valence manganite Pb3Mn7O15
- 2016
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Ingår i: Journal of materials science. Materials in electronics. - : Springer Science and Business Media LLC. - 0957-4522 .- 1573-482X. ; 27:12, s. 12562-12573
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Tidskriftsartikel (refereegranskat)abstract
- The structural, magnetic, and dielectric properties of Pb3Mn7O15 have been investigated using high-quality single crystals. Pb3Mn7O15 adopts a pseudo-hexagonal orthorhombic structure, with partially filled Kagom, layers connected by ribbons of edge-sharing MnO6 octahedra and intercalated Pb cations. There are 9 inequivalent sites in the structure for the Mn ions, which exist both as Mn3+ and Mn4+. Pb3Mn7O15 undergoes an antiferromagnetic transition below T-N similar to 67 K, with significant geometric frustration. Neutron powder diffraction on crushed single crystals allowed us to determine the low-temperature antiferromagnetic magnetic structure. We discuss the magnetic interaction pathways in the structure and possible interplay between the structural distortions imprinted by the lone-electron pair of Pb2+ cations and Mn3+/Mn4+ charge ordering.
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| 17. |
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| 18. |
- Leo, N., et al.
(författare)
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Magnetoelectric inversion of domain patterns
- 2018
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 560:7719, s. 466-
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Tidskriftsartikel (refereegranskat)abstract
- The inversion of inhomogeneous physical states has great technological importance; for example, active noise reduction relies on the emission of an inverted sound wave that interferes destructively with the noise of the emitter(1), and inverting the evolution of a spin system by using a magnetic-field pulse enables magnetic resonance tomography(2). In contrast to these examples, inversion of a distribution of ferromagnetic or ferroelectric domains within a material is surprisingly difficult: field poling creates a single-domain state, and piece-by-piece inversion using a scanning tip is impractical. Here we report inversion of entire ferromagnetic and ferroelectric domain patterns in the magnetoelectric material Co3TeO6 and the multiferroic material Mn2GeO4, respectively. In these materials, an applied magnetic field reverses the magnetization or polarization, respectively, of each domain, but leaves the domain pattern intact. Landau theory indicates that this type of magnetoelectric inversion is universal across materials that exhibit complex ordering, with one order parameter holding the memory of the domain structure and another setting its overall sign. Domain-pattern inversion is only one example of a previously unnoticed effect in systems such as multiferroics, in which several order parameters are available for combination. Exploring these effects could therefore advance multiferroics towards new levels of functionality.
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| 19. |
- Mathieu, Roland, et al.
(författare)
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Dynamical studies on model spin glasses
- 2010
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Ingår i: International Conference on Magnetism (ICM 2009). - : IOP Publishing. ; , s. 032042-
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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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| 20. |
- Mathieu, Roland, et al.
(författare)
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Isothermal remanent magnetization and the spin dimensionality of spin glasses
- 2010
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Ingår i: Philosophical Magazine Letters. - : Informa UK Limited. - 0950-0839 .- 1362-3036. ; 90:10, s. 723-729
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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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| 21. |
- Mathieu, Roland, et al.
(författare)
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Magnetic order near 270 K in mineral and synthetic Mn2FeSbO6 ilmenite
- 2011
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 98:20, s. 202505-1-202505-3
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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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| 22. |
- Mathieu, Roland, et al.
(författare)
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Memory and rejuvenation in a spin glass
- 2010
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Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 90:6, s. 67003-
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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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| 23. |
- Pancaldi, Matteo, 1989-, et al.
(författare)
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Spiral metamaterials for terahertz magnetic field enhancement
- 2019
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Ingår i: META 2019 Lisbon - Portugal. - : META Conference. ; , s. 1343-1344
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Konferensbidrag (refereegranskat)abstract
- We designed a class of spiral thin-film antennas for enhancing, in the near field, the incident terahertz (THz) magnetic field. Indeed, using existing laser-based THz sources, our metamaterial geometry allows generating magnetic fields of the order of 2 T over a time scale of few picoseconds, enabling the investigation of nonlinear ultrafast spin dynamics in table-top experiments.
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| 24. |
- Peddis, D., et al.
(författare)
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Memory and superposition in a superspin glass
- 2021
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- The non-equilibrium dynamics of the superspin glass state of a dense assembly of similar to 2 nm MnFe2O4 nanoparticles was investigated by means of magnetization, ac susceptibility and Mossbauer spectroscopy measurements and compared to the results of Monte Carlo simulations for a mesoscopic model that includes particles morphology and interparticle interactions. The zero-field cooled (ZFC), thermoremanent (TRM), and isothermal remanent magnetization (IRM) were recorded after specific cooling protocols and compared to those of archetypal spin glasses and their dimensionality. The system is found to display glassy magnetic features. We illustrate in detail, by a number of experiments, the dynamical properties of the low-temperature superspin glass phase. We observe that these glassy features are quite similar to those of atomic spin glasses. Some differences are observed, and interestingly, the non-atomic nature of the superspin glass is also reflected by an observed superspin dimensionality crossover. Monte Carlo simulations-that explicitly take into account core and surface contributions to the magnetic properties of these ultrasmall nanoparticles in direct contact, as well as interparticle interactions-evidence effects of the interplay between (intraparticle) core/surface exchange coupling and (interparticle) dipolar and exchange interactions.
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| 25. |
- Polley, Debanjan, et al.
(författare)
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THz-driven demagnetization with perpendicular magnetic anisotropy : towards ultrafast ballistic switching
- 2018
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Ingår i: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 51:8
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Tidskriftsartikel (refereegranskat)abstract
- We study THz-driven spin dynamics in thin CoPt films with perpendicular magnetic anisotropy. Femtosecond magneto-optical Kerr effect measurements show that demagnetization amplitude of about 1% can be achieved with a peak THz electric field of 300 kV cm(-1), and a corresponding peak magnetic field of 0.1 T. The effect is more than an order of magnitude larger than observed in samples with easy-plane anisotropy irradiated with the same field strength. We also utilize finite-element simulations to design a meta-material structure that can enhance the THz magnetic field by more than an order of magnitude, over an area of several tens of square micrometers. Magnetic fields exceeding 1 Tesla, generated in such meta-materials with the available laser-based THz sources, are expected to produce full magnetization reversal via ultrafast ballistic precession driven by the THz radiation. Our results demonstrate the possibility of table-top ultrafast magnetization reversal induced by THz radiation.
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| 26. |
- Scalera, V., et al.
(författare)
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Analysis in k-Space of Magnetization Dynamics Driven by Strong Terahertz Fields
- 2021
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Ingår i: IEEE transactions on magnetics. - 0018-9464 .- 1941-0069. ; 57:2
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Tidskriftsartikel (refereegranskat)abstract
- Demagnetization in a thin film due to a terahertz pulse of magnetic field is investigated. Linearized Landau-Lifshitz-Gilbert (LLG) equation in the Fourier space to describe the magnetization dynamics is derived, and spin wave time evolution is studied. Finally, the demagnetization due to spin wave dynamics and recent experimental observations on similar magnetic system is compared. As a result, the marginal role of spin wave dynamics in loss of magnetization is established.
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| 27. |
- Toledano, Pierre, et al.
(författare)
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First-order multi-k phase transitions and magnetoelectric effects in multiferroic Co3TeO6
- 2012
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 85:21, s. 214439-
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Tidskriftsartikel (refereegranskat)abstract
- A theoretical description of the sequence of magnetic phases in Co3TeO6 is presented. The strongly first-order character of the transition to the commensurate multiferroic ground state, induced by coupled order parameters corresponding to different wave vectors, is related to a large magnetoelastic effect with an exchange energy critically sensitive to the interatomic spacing. The monoclinic magnetic symmetry C2' of the multiferroic phase permits spontaneous polarization and magnetization as well as the linear magnetoelectric effect. The existence of weakly ferromagnetic domains is verified experimentally by second harmonic generation measurements.
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| 28. |
- Willa, K., et al.
(författare)
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Nanocalorimeter platform for in situ specific heat measurements and x-ray diffraction at low temperature
- 2017
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Ingår i: Review of Scientific Instruments. - Melville, NY : AIP Publishing. - 0034-6748 .- 1089-7623. ; 88:12
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Tidskriftsartikel (refereegranskat)abstract
- Recent advances in electronics and nanofabrication have enabled membrane-based nanocalorimetry for measurements of the specific heat of microgram-sized samples. We have integrated a nanocalorimeter platform into a 4.5 T split-pair vertical-field magnet to allow for the simultaneous measurement of the specific heat and x-ray scattering in magnetic fields and at temperatures as low as 4 K. This multi-modal approach empowers researchers to directly correlate scattering experiments with insights from thermodynamic properties including structural, electronic, orbital, and magnetic phase transitions. The use of a nanocalorimeter sample platform enables numerous technical advantages: precise measurement and control of the sample temperature, quantification of beam heating effects, fast and precise positioning of the sample in the x-ray beam, and fast acquisition of x-ray scans over a wide temperature range without the need for time-consuming re-centering and re-alignment. Furthermore, on an YBa2Cu3O7-delta crystal and a copper foil, we demonstrate a novel approach to x-ray absorption spectroscopy by monitoring the change in sample temperature as a function of incident photon energy. Finally, we illustrate the new insights that can be gained from in situ structural and thermodynamic measurements by investigating the superheated state occurring at the first-order magneto-elastic phase transition of Fe2P, a material that is of interest for magnetocaloric applications.
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