Synthesis and Magnetic Properties of Silver-Doped Iron Dichromium Tetrasulfide
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hesis and Magnetic Properties of Silver-Doped Iron Dichromium Tetrasulfide T. G. Aminova, *, G. G. Shabuninaa, and E. V. Bushevaa aKurnakov
Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Leninskii pr. 31, Moscow, 119991 Russia *e-mail: [email protected]
Received December 5, 2019; revised March 6, 2020; accepted March 25, 2020
Abstract—We have synthesized Fe1 – xAgxCr2S4 (0 < x < 0.5) solid solutions via doping of the FeCr2S4 thiochromite with silver. From a break in the composition dependence of the unit-cell parameter for the synthesized materials, the solid solution series has been shown to be limited by x = 0.22. The magnetic properties of the solid solutions have been studied at temperatures from 4 to 300 K in a magnetic field H = 3980 A/m (50 Oe). All of the materials have been shown to be ferrimagnets with a Curie temperature rising with silver concentration: from 185 K at x = 0 to 203 K at x = 0.22. We have determined saturation magnetic moments of the solid solutions and proposed a model that accounts for their observed magnetic properties. Keywords: magnetic semiconductor, spin glass, chalcogenide spinel DOI: 10.1134/S0020168520080014
INTRODUCTION This work deals with the synthesis and characterization of new magnetically active phases based on silver-doped iron dichromium tetrasulfide. Interest in chromium chalcogenide spinels, more precisely, in FeCr2S4, is aroused by the fact that this compound has unique properties, such as a giant magnetoresistance [1, 2], large magnetoelectric parameters [3–6], and giant Kerr rotation, and exhibits unusual low-temperature magnetic behavior, known as a complex orbital state [7–11]. These properties are partially inherent in FeCr2S4-based solid solutions as well. Iron dichromium tetrasulfide (FeCr2S4) has ferrimagnetic properties (Tc = 177–185 K) and the normal spinel structure (sp. gr. Fd3m). According to Wilkinson et al. [12] and Shirane et al. [13], the magnetic moments of the Fe2+ and Cr3+ ions in FeCr2S4 at 4.2 K are 4.2μB and 2.9μB, respectively. The magnetic moment per formula unit of FeCr2S4, 1.6μB, agrees well with the moment calculated for a simple collinear ferrimagnetic structure [14–17]. The temperature behavior of the inverse paramagnetic susceptibility of this compound also points to ferrimagnetic ordering. Below its Curie temperature, the σ(Т)ZFC and σ(Т)FC magnetization curves of FeCr2S4 demonstrate irreversible behavior for T < 100 K and its σ(T) has an anomaly at ~70 K because of the sharp rise in magnetic anisotropy constant. As the temperature is lowered to below 70 K, the ZFC and FC magnetization curves fall off and then exhibit opposite behaviors,
which can be accounted for in terms of the structural transition at 9 K, due to orbital ordering [18–21]. That FeCr2S4 undergoes a phase transition at a temperature near 60 K was confirmed previously by transmission electron microscopy and static and dynamic magnetic susceptibility measurements [22–24]. As shown by Tsurkan et al. [25] in a muon spin relaxation study, at ~
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