Short-range ordering in the spin glass system ZnCr2xAl2-2xS4

Abstract

Neutron diffraction investigations have been performed on ZnCr2xAl2-2xS4 in the range 0.5 or=0.85 a helimagnetic ordering builds up below TN which is transformed at T0 into a mixed phase. Below x<or=0.80 no long-range magnetic ordering was detected, reflecting the presence of a spin glass (SG) state. Strong spin correlations occur below 100K giving rise to important diffuse scattering contributions. The short-range ordering in the SG state is of the same nature as that in concentrated samples above TN: locally the magnetic moments are arranged in a ferromagnetic (001) plane and turn by an angle of about 71 degrees from plane to plane. The correlation function gamma i increases continuously with decreasing temperature. No anomaly or saturation was observed at the freezing temperature Tf below which the correlation length still increases, gamma 1 scales characteristically with x2 which agrees fairly well with a high-temperature series expansion approach above T=20K including first- and second-nearest-neighbour interactions (J1=2K, J2 approximately=-2K). The inverse correlation length 1/ xi decreases linearly with temperature leading to a finite value at T=0 in the SG state.