Electron spin resonance spectroscopy of layered chromium silver chalcogenides

Abstract

Electron spin resonance and magnetic susceptibilities of the layered superionic conductors AgCrS₂ and AgCrSe₂ have been studied between 4 and 300 K. These compounds undergo magnetic phase transitions both within and between the layers of Cr³⁺ ions. At 295 K, polycrystalline AgCrS₂ gave g= 1.982, ΔH_pp 410 G; AgCrSe₂ gave g= 1.989, ΔH_pp= 385 G. On cooling towards the respective Néel temperatures T_N of 42 and 55 K, the e.s.r. linewidths diverge with critical exponents close to 0.66, typical of two-dimensional antiferromagnetic systems. Magnetic ordering between the Cr³⁺ layers commences more than 100 K above the Néel temperatures. Supercooling effects have also been observed. Some differences in the e.s.r. behaviour of the two compounds were found. The g value of AgCrSe₂ increased on close approach to T_N from above, whereas that of AgCrS₂ decreased. A strong, broad resonance with a temperature-dependent g value was observed below T_N from AgCrSe₂, but not from AgCrS₂. These effects can be related to differences in magnetic structure within the Cr³⁺ layers. There is little magnetic evidence for a structural phase transition reported to occur at 160 K in AgCrS₂.