| 11. |
- 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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| 12. |
- 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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| 13. |
- 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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| 14. |
- 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
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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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| 15. |
- Ivanov, Sergey A., et al.
(författare)
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Structural and magnetic properties of nickel antimony ferrospinels
- 2015
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Ingår i: Materials Chemistry and Physics. - : Elsevier BV. - 0254-0584 .- 1879-3312. ; 158, s. 127-137
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Tidskriftsartikel (refereegranskat)abstract
- Spinel-type compounds of Fe-Ni-Sb-O system were synthesized as polycrystalline powders. The crystal and magnetic properties were investigated using X-ray and neutron powder diffraction, Mossbauer and X-ray absorption spectroscopy and magnetization measurements. The samples crystallize in the cubic system, space group Fd - 3 m. The distribution of cations between octahedral and tetrahedral sites was refined from the diffraction data sets using constraints imposed by the magnetic, Mossbauer and EDS results and the ionic radii. The cation distribution and the temperature dependence of the lattice parameter (a) and the oxygen positional parameter (u) were obtained. A chemical formula close to Fe0.8Ni1.8Sb0.4O4 was determined, with Sb5+ cations occupying octahedral sites, and Fe3+ and Ni2+ occupying both tetrahedral and octahedral sites. Fe3+ mainly (85/15 ratio) occupy tetrahedral sites, and conversely Ni2+ mainly reside on octahedral ones. The magnetic unit cell is the same as the crystallographic one, having identical symmetry relations. The results indicate that the compounds have a collinear ferrimagnetic structure with antiferromagnetic coupling between the tetrahedral (A) and octahedral (B) sites. Uniquely, the temperature dependence of the net magnetization of this rare earth free ferrimagnet exhibits a compensation point.
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| 16. |
- 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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| 17. |
- 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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| 18. |
- Ivanov, Sergey, et al.
(författare)
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Cation ordering, ferrimagnetism and ferroelectric relaxor behavior in Pb(Fe1-xScx)(2/3)W1/3O3 solid solutions
- 2019
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Ingår i: European Physical Journal B. - : SPRINGER. - 1434-6028 .- 1434-6036. ; 92:8
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Tidskriftsartikel (refereegranskat)abstract
- Ceramic samples of the multiferroic perovskite Pb(Fe1-xScx)(2/3)W1/3O3 with 0 <= x <= 0.4 have been synthesized using a conventional solid-state reaction method, and investigated experimentally and theoretically using first-principle calculations. Rietveld analyses of joint synchrotron X-ray and neutron diffraction patterns show the formation of a pure crystalline phase with cubic (Fm3(_)m) structure with partial ordering in the B-sites. The replacement of Fe by Sc leads to the increase of the cation order between the B and B '' sites. As the non-magnetic Sc3+ ions replace the magnetic Fe3+ cations, the antiferromagnetic state of PbFe2/3W1/3O3 is turned into a ferrimagnetic state reflecting the different magnitude of the magnetic moments on the B ' and B '' sites. The materials remain ferroelectric relaxors with increasing Sc content. Results from experiments on annealed and quenched samples show that the cooling rate after high temperature annealing controls the degree of cationic order in Pb(Fe1-xScx)(2/3)W1/3O3 and possibly also in the undoped PbFe2/3W1/3O3.
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| 19. |
- 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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| 20. |
- 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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