Paramagnetic—spin-glass—antiferromagnetic phase transitions inCd1−xMnxTefrom specific heat and magnetic susceptibility measurements

Abstract

Low-temperature specific heat and low-field magnetic susceptibility were measured in ${\mathrm{Cd}}_{1-x}{\mathrm{Mn}}_x\mathrm{Te}$ mixed crystals for $0.002<~x<~0.70$. Three regions of composition can be distinguished in both experiments. For $x<\mathrm{}0.17\mathrm{}$ the crystal is paramagnetic at all temperatures. For $0.17<x<\mathrm{}0.7\mathrm{}$, a spin-glass phase is observed, as evidenced by the characteristic cusp in the susceptibility and a linear temperature dependence of the specific heat in the low-temperature regions. Because the material is an insulator at low temperatures, and the Mn interactions are only antiferromagnetic, we believe that the observed spin-glass phase is produced by the frustration of the lattice. For $x=0.7\mathrm{}$ an antiferromagnetic phase is observed. To understand the experimental behavior of the specific heat and susceptibility as a function of temperature and magnetic field for $0.002<x<\mathrm{}0.17\mathrm{}$, we must assume that the distribution of Mn ions deviates strongly from a random distribution. The number of pairs is more than doubled for $x=0.05\mathrm{}$, and 30% higher for $x=0.1\mathrm{}$, than statistically predicted. The number of larger clusters, like triplets, is also significantly higher. Analysis of the data yielded the value of the exchange integral for the nearest-neighbor interaction to be $\frac{J_{\mathrm{NN}}}{k}=-0.55\mathrm{}\pm 0.05$ K. The interaction is stronger within the larger clusters, and is described by a different exchange constant $\frac{J_{\mathrm{NN}}^{\prime }}{k}=-4.3\mathrm{}$ K.