Методом твердофазного синтеза получено новое магнитное соединение NaNiFe2(VO4)3, приведены результаты изучения методами рентгеновской дифракции, гамма-резонанса и магнитометрии. Кристаллическая структура многокомпонентного ванадата описывается триклинной пространственной группой симметрии P1. Элементарная ячейка содержит шесть неэквивалентных смешанных катионных позиций, занятых разновалентными ионами переходных металлов железа Fe3+ и никеля Ni2+, что способствует реализации состояния с локальным нарушением зарядовой нейтральности. Кроме того, обнаружено наличие двух типов позиций атомов железа: с кислородным окружением как в виде октаэдров, так и квадратных пирамид с неравновероятной их заселенностью железом и никелем. Ход температурной и полевой зависимостей намагниченности в широком температурном интервале характерен для парамагнетика, содержащего ферромагнитные кластеры. Ключевые слова: многокомпонентные ванадаты, кристаллическая структура, магнитные свойства.

Polycrystalline HoFeTi2O7 samples were obtained by solid-phase synthesis and studied by X-ray diffraction, gamma resonance, and SQUID methods. The characteristics of structural properties are presented, indicating the distribution of iron atoms over nonequivalent crystallographic positions and their uneven filling in the positions mixed with titanium. Spin disorder formed by mixing magnetic and nonmagnetic ions, spatial inhomogeneity of interactions that determine the magnetic structure in the crystal leads to the formation of competing exchange magnetic interactions between the nearest neighbors, frustration of magnetic bonds and the absence of long-range magnetic order. It has been shown that the temperature dependence of the static magnetic susceptibility at low temperatures has features characteristic of the spin glass magnetic state.

Методами мессбауэровской спектроскопии и ферромагнитного резонанса изучены порошки гематита после ультразвуковой обработки в режиме кавитации в водной суспензии и в водной суспензии с органической составляющей (белок альбумин). Обнаружено формирование новой магнитной фазы после ультразвуковой обработки суспензий с альбумином. Магнитные параметры новой фазы совпадают с соответствующими параметрами металлической фазы alpha-Fe. DOI: 10.21883/PJTF.2017.24.45334.16984

The results of the study of structural, thermal, static magnetic and resonance properties of the low-dimensional compound NaCuFe2(VO4)3 prepared by the standard solid-phase reaction method are presented. In the temperature range 110–300 K and in the X-band, an electron paramagnetic resonance was observed, characterized by a g-factor equal to 2.008. The magnetic properties of the sample with a high level of frustrations in the paramagnetic, antiferromagnetic, and disordered states are investigated. A shift of the Néel temperature to high temperatures under the influence of an external magnetic field was detected. The reasons for the appearance of disordered magnetism in NaCuFe2 (VO4) 3 are discussed. The features of the effect of sodium substitution by lithium on the physical properties of the ACuFe2 (VO4) 3 (A = Na, Li) system are revealed. It is shown that under the influence of chemical pressure there is a transformation of lattice parameters, distances between magnetic ions, crystallite size, which leads to a change in physical properties.

A new magnetic compound NaZnFe2(VO4)3 obtained by solid-phase synthesis has been studied using X-ray diffraction, Mössbauer spectroscopy, electron paramagnetic resonance, measurement of the temperature dependence of the dielectric permeability, and magnetometry. The crystalline structure of NaZnFe2(VO4)3 is described by a triclinic spatial group of symmetry P1 with the parameters of an elementary crystalline chain: a = 6.74318 (7) Å, b = 8.1729 (1) Å, c = 9.8421 (1) Å, α = 106.2611 (9)º, β = 104.55 (1)º, γ = 102.337 (1)º, V = 479.88 (1) Å3, Z = 2. Magnetic Fe3+ cations in the cell occupy six positions populated together with diamagnetic Zn2+ cations, which leads to states of magnetic inhomogeneity and local violation of charge neutrality. Data from resonance and magnetic studies of NaZnFe2(VO4)3 confirm the main role of high-spin Fe3+ iron cations in the formation of magnetism with competing exchange magnetic interactions and a high value of the frustration index. It is shown that the magnetic subsystem of a sample with a negative asymptotic Neel temperature undergoes a magnetic transition from the paramagnetic state to the magnetic state of the spin glass when the temperature decreases. T.V. Drokina 1, M.S. Molokeev M.C. 1, 2, D.A. Velikanov 1, O.A. Bayukov 1, A.M. Vorotynov 1, A.L. Freidman 1, G.A. Petrakovskii 1 1 L.V. Kirensky Institute of Physics, Federal Research Center KSC Siberian Branch of Russian Academy of Science, Krasnoyarsk, 660036, Russia 2 Siberian Federal University, Krasnoyarsk, 660074, Russia