| 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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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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| 3. |
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| 4. |
- 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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| 5. |
- Kaleva, G M, et al.
(författare)
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Phase Transitions of (Cu,Ni)(3)TeO(6) Solid Solutions
- 2011
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Ingår i: Inorganic Materials (Neorganicheskie materialy). - 0020-1685 .- 1608-3172. ; 47:10, s. 1132-1140
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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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| 6. |
- Kaleva, G. M., et al.
(författare)
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Preparation, electrical conductivity, and magnetic susceptibility of (Ba1-x Bi (x) )(Mn0.5+x/2Nb0.5-x/2)O-3
- 2013
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Ingår i: Inorganic Materials (Neorganicheskie materialy). - 0020-1685 .- 1608-3172. ; 49:5, s. 513-516
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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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