A new ferromagnetic thiospinel CuCrZrS₄with re-entrant spin-glass behaviour

Abstract

A new thiospinel CuCrZrS 4 has been successfully synthesized by a solid-state chemical reaction. This CuCrZrS 4 exhibits ferromagnetic properties below the Curie temperature at T c = 60 ± 2 K. The appearance of irreversibility between field-cooled (F.C.) and zero-field cooled (Z.F.C.) magnetization is prominent below around 5 K in less than 150 Oe. The ac susceptibility χ AC shows a rapid decrease below ≈10 K. This low-magnetic field behaviour indicates the existence of a reentrant spin glass phase below ≈10 K. The d.c. magnetic susceptibility above 100 K shows Curie-Weiss behaviour with the effective magnetic moment of 3.61 µ B , which is a little less than the spin only value of 3.87 µ B for Cr 3+ ion. The asymptotic Curie temperature θ p is approximately 65 K which is a little higher than T c. The valence state is confirmed to be Cu + Cr 3+ Zr 4+ S 2-4 on the basis of magnetic properties. Electrical resistivity ρ shows a semiconducting temperature dependence over the temperature range 4.2 to 280 K with an activation energy of 6.84×10-3 eV in the higher temperature range 50 to 283 K.

Magnetic and thermodynamic properties of the thiospinel compoundCuCrZrS4

“…The effective magnetic moment eff obtained from C is 3.48 B , which is close to the value of 3.87 B expected for the free Cr 3+ ion. As was pointed out by Iijima et al, 21 a large irreversibility between FC and ZFC is observed in the low-temperature range as shown in Fig. 1͑b͒.…”

“…21 High-purity fine powders of Cu ͑99.99%͒, Cr ͑99.99%͒, Zr ͑99.9%͒, and S ͑99.999%͒ were mixed in stoichiometric ratio and were reacted in a quartz tube at 1023 K for seven days. A powder specimen was reground, pressed into a rectangular bar with an aspect ratio of 1:5, and sintered at 1023 K for two days.…”

“…When half of the Cr ions of CuCr 2 S 4 are substituted by Zr ions, the electric configuration is Cu 1+ Cr 3+ Zr 4+ S 4 2− , and the transport properties become semiconductive. 21 This behavior can be explained by a variable range-hopping ͑VRH͒ conduction. 31 This means that the number of conduction electrons in CuCrZrS 4 decrease with decreasing temperature.…”

“…in this compound is attributed to the double-exchange interaction between the Cr 3+ and Cr 4+ cations via the conduction electrons. [18][19][20] High-purity specimens of CuCrZrS 4 were recently synthesized and investigated through transport and magnetic measurements by Iijima et al 21 When Zr ions occupy half of the B sites of CuCr 2 S 4 , the temperature dependence of the electric resistivity changes from metallic to semiconducting with an energy gap of 79 K. The Curie temperature simultaneously decreases to 60 K. In addition, spin-glass behavior is observed below the freezing temperature T f = 10 K, namely, CuCrZrS 4 shows reentrant spin-glass freezing from the longrange ferromagnetic order. It has been confirmed that the ionic configuration of this compound is Cu 1+ Cr 3+ Zr 4+ S 4 2− .…”

Large negative magnetoresistance in thiospinel CuCrZrS4

“…Spinel CuCr 2 S 4 is a well known metallic and ferromagnetic compound with the Curie temperature T C of about 400 K. [8][9][10][11] Recently, spinel CuCrZrS 4 was obtained by substituting half of Cr by Zr. [12] It has the same normal spinel structure with Cu in the A site, which is tetrahedrally coordinated with S, and Cr and Zr in the B site, which is octahedrally coordinated. By this substitution, T C is decreased to about 60 K. In addition, a successive magnetic transition suggesting reentrant spin glass was observed at the temperature T G ≈ 10 K. As for the electrical properties, semiconducting behavior of the resistivity was observed.…”