High-Pressure Synthesis, Crystal Structure, and Physical Properties of a Spinel Compound Co_0.7Al₂S₄

Abstract

In this paper, we report on the discovery of a spinel compound, Co 0.7 Al 2 S 4 , which was synthesized at high-pressure. The systematic characterizations were carried out by structural, magnetic, and heat capacity measurements. The compound crystallizes into a cubic structure with the space group Fd3̅ m (no. 227) and the lattice constant a = 9.9580(1) Å. Magnetic susceptibility measurements suggest that Co 0.7 Al 2 S 4 exhibits a spin glass ground state, freezing at T f ∼ 7.2 K with a Weiss temperature T θ ∼ −115.9 K, which is verified by ac magnetic susceptibility and heat capacity measurements. The frustration parameter f for Co 0.7 Al 2 S 4 is calculated to be about 16.6, based on the formula f = | T θ /T f |, indicating that Co 0.7 Al 2 S 4 is a high-frustration magnet. Specific heat data displays a T 2 dependence below the freezing temperature, which is different from the linear dependence observed in a common spin glass system. Compared with the similar compound CoAl 2 O 4 , it is suggested that the vacancies in the Co sites should be responsible for the occurrence of the spin glass behavior of Co 0.7 Al 2 S 4 .

Local mechanism for magnetoelastic coupling and magnetic frustration in high-pressure synthetized NixTi2S4 intercalated sulfide

“…In fact, the stabilization of these intercalation products is performed through solid-state synthesis or novel high-pressure synthesis procedures. 15–17 Specifically, high pressure can reduce atomic distances and promote chemical reactions that are typically hindered under normal ambient pressure conditions. 18…”