Influence of temperature on the critical fields in ZnCr 2− xAl xSe 4 antiferromagnets

Abstract

The critical fields were investigated by the ac susceptibility χ ac (B) and the magnetic moment μ(B) in the antiferromagnetic semiconductors of the ZnCr 2− x Al x Se 4 spinel system in the compositional range 0.13 ≤ x ≤ 0.4. The both dependences χ ac (B) and μ(B) revealed two maxima at critical fields H c1 characteristic for metamagnetic threshold where the simple spin spiral transforms into conical magnetic structure and at H c2 where the conical magnetic structure transforms into ferromagnetic phase. With increasing temperature a peak at critical field H c2 shifts into lower values of the magnetic field while a peak at H c1 remains unchanged. These results point to a strong antiferromagnetic superexchange interaction in the range of magnetic ordering which does not significantly depend on temperature, Al content and magnetic field. The opposite behaviour in the case of the ferromagnetic exchange interaction was observed.