| 1. |
- 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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| 2. |
- Ivanov, Sergey A., et al.
(författare)
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Crystal structure and antiferromagnetic spin ordering of LnFe(2/3)Mo(1/3)O(3) (Ln = Nd, Pr, Ce, La) perovskites
- 2015
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 91:9
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Tidskriftsartikel (refereegranskat)abstract
- Stoichiometric polycrystalline samples of LnFe(2/3)Mo(1/3)O(3) (Ln = Nd, Pr, Ce, La) have been prepared by solid-state reaction and studied by means of x-ray and neutron powder diffraction as well as Mossbauer spectroscopy and magnetic measurements. All samples were found to be of single phase and to have Pnma symmetry with valence state +3 of Fe and Mo. It is demonstrated that the B-site cations of LnFe(2/3)Mo(1/3)O(3) in accord with LnFeO(3) order in a G-type antiferromagnetic structure with the magnetic moments aligned along the b axis. However, with significantly lower Neel temperatures than their LnFeO(3) parent compounds. The Fe-O-Fe bond lengths and bond angles and thus themagnitude of the antiferromagnetic superexchange interaction are found to systematically change with the ionic radius of Ln such that T-N increases with increasing radius. Only the CeFe2/3Mo1/3O3 compound experiences a low temperature spin reorientation from alignment along the b axis to the a axis.
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| 3. |
- 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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| 4. |
- Ivanov, Sergey A., et al.
(författare)
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New insights into the multiferroic properties of Mn3TeO6
- 2017
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Ingår i: Journal of Physics D. - : IOP PUBLISHING LTD. - 0022-3727 .- 1361-6463. ; 50:8
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Tidskriftsartikel (refereegranskat)abstract
- Mn3TeO6 has a trigonal corundum related structure (space group R (3) over bar), and orders in an incommensurate antiferromagnetic (AFM) structure at T-N approximate to 24 K. A weak ferroelectric order below T* similar to 21 K has recently been reported. In order to investigate possible structural changes below T-N leading to the observed dipole order, we have performed a detailed study of the crystal and magnetic structures of Mn3TeO6 using neutron powder diffraction (NPD) in the temperature range of 5-40 K. Complementary low-temperature second harmonic generation (SHG) measurements were performed in order to confirm the reported dipole order at T*. No change in the rhombohedral symmetry associated with a possible displacive phase transition at T* was observed in the long-range structural correlations, and it appears that Mn3TeO6 keeps the same incommensurately modulated magnetic spin structure with the propagation vector k = (0; 0; 0.43) in the whole temperature range from 5 to 24 K.
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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
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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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Perovskite solid solutions La0.75Bi0.25Fe1-xCrxO3 : Preparation, structural, and magnetic properties
- 2017
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Ingår i: Journal of Solid State Chemistry. - : Elsevier. - 0022-4596 .- 1095-726X. ; 254, s. 166-177
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Tidskriftsartikel (refereegranskat)abstract
- Solid solutions of La0.75Bi0.25Fe1−xCrxO3 (x = 0.1, 0.25, 0.5, and 0.75) prepared by conventional solid state reaction have been studied by means of X-ray powder diffraction (XRPD), neutron powder diffraction (NPD) and magnetic measurements. The NPD and XRPD patterns indicate orthorhombic structure (space group Pnma) for all compositions in the whole temperature range investigated (4–900 K). The lattice parameters of La0.75Bi0.25Fe1−xCrxO3 were found to decrease with the Cr content. It was established that the Fe3+ and Cr3+ cations are randomly positioned at the B-site of the perovskite structure.All samples order antiferromagnetically below transition temperatures that decrease with increasing Cr content, from around 700 K for x = 0.1 to about 300 K for x = 0.75. The antiferromagnetic arrangement of the Fe3+/Cr3+ magnetic moments in the B-site is of G-type along the x-axis (Gx mode) with propagation vector k = (0,0,0) for all concentrations of Cr. Effects of the composition on several structural distortion parameters were investigated and an anomalous variation of the octahedral deformation with Cr content was found. Whilst the overall octahedral deformation varies irregularly with increasing Cr content, the octahedral tilting was found to decrease monotoneously.
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| 7. |
- 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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| 8. |
- 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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| 9. |
- 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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| 10. |
- 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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