Magnetic properties of stuffed copper chromium tellurides Cu1+xCr2+yTe4 (x=0–1, y<0.3)

We present a detail study of the effect of excess metal atoms on the magnetic properties of Cu1+xCr2+yTe4 at 2–400 K. With the increase in x=0–1 and y<0.3, these compounds retain metallic behavior, while ferromagnetic ordering temperature reduces from 325 to 160 K. Our low field susceptibility χac measurements reveal a second transition on cooling below the ferromagnetic ordering; the transition at around 160–180 K intensifies with the excess amount of copper and chromium atoms. The value of spontaneous magnetization at 2 K remains between 2.6 and 2.9μB across all the compositions and it reduces with temperature as M(T)∼A0T3/2+A1T5/2, as expected for the excitation of Bloch's spin waves in a model of the Heisenberg ferromagnet. Our terminal composition Cu1.9Cr2.25Te4 showed only second transition at 160 K with short range magnetic order much above the transition temperature and in the absence of the specific heat jump at this temperature. The magnetic properties are explained as a result of random magnetic anisotropy in the excess-metal compositions induced by the interstitial atomic defects in their parent spinel structure. The large stuffing of cations has been made possible in the telluride compounds because of the large size of tellurium and also by the covalent bonding that stabilizes the defect structure.

► Magnetization measurement of ferromagnetic Cu1+xCr2+yTe4, x=0–1 at 2–400 K. ► Reduction of TC with no significant changes in the magnetization by the stuffing. ► A broad bump in CP around the magnetic transition in the stuffed composition Cu1.9Cr2.2Te4. ► Extensive short range ordering in its paramagnetic phase. ► Analysis of T3/2-dependence of M(T) and Cp(T) using Bloch's theory of spin-wave.