G.V. Bazuev

Investigation of the magnetic phase transition and magnetocaloric properties of the Mn2FeSbO6 ilmenite

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.

Successive phase transitions in the orthovanadate TmVO3

Synthesis and crystal structure, magnetization and heat capacity measurements of phase pure polycrystalline TmVO3 are reported. TmVO3 was stabilized in the orthorhombic structure by thermal treatment of the precursor TmVO4 in a reducing atmosphere. Magnetization and heat capacity measurements reveal the presence of several successive structural and magnetic phase transitions in this compound. At T = 108 K, the sample undergoes a transition from a paramagnetic state to an antiferromagnetic state, followed by a second transition at 78 K which is related to spin and orbital reorientation. The heat capacity measurements reveal the presence of a third transition in the paramagnetic state (at T = 175 K), which corresponds to a structural phase transition and orbital ordering. At low temperatures (~15 K) and weak fields, there is an anomaly in the magnetization, which may be associated with antiferromagnetic short range ordering of the Tm3+ ions.

Synthesis and magnetic properties of a new complex oxide Mn3FeTiSbO9 with an ilmenite structure

Synthesis of MTiO3 ilmenites is easy to accomplish under common conditions in air or an inert atmo sphere from simple metal oxides. After thermobaric treatment, these compounds acquire a perovskite or LiNbO3 structure [5]; in the latter case, titanates simultaneously exhibit weak ferromagnetism and spontaneous polarization, i.e. become multiferroics [6, 7]. Magnetoelectric materials, in which ferroelec tric and ferromagnetic properties are combined, are of considerable interest since they are candidates for use in nanoelectronics and spintronics [7]. However, MTiO3 titanates with ilmenite and LiNbO3 structures have very low magnetic ordering temperatures (40– 120 K).

Dilute ferrimagnetism of ilmenites Mn3FeTiSbO9 and Mn4FeTi2SbO12

Metastable solid solutions (SS) Mn3FeTiSbO9 and Mn4FeTi2SbO12 with the ilmenite structure (space group R

Crystal and Magnetic Structures of Ba4Mn3O10

\bar 3

Crystal structure and magnetic properties of double perovskite Mn2FeSbO6

) have been prepared by quenching at normal conditions. The compositions of the compounds have been justified using EDX spectroscopy and X-ray diffraction. The magnetic properties of SSs have been analyzed by comparison with ferrimagnetic ilmenite Mn2FeSbO6 (TN = 269 K) as a natural mineral and ceramics obtained at high pressure and high temperature. The solid solutions have been characterized as dilute magnetic systems formed as a result of substitution of nonmagnetic cations Ti4+ for a part of Fe3+ and Sb5+ cations. Mn3FeTiSbO9 is considered as a ferromagnetic with TN = 171 K and Mn4FeTi2SbO12 as a magnetic with the concentration of magnetic clusters below the percolation threshold.