Magnetic properties of stuffed copper chromium tellurides Cu 1+ xCr 2+ yTe 4 ( x=0–1, y

Abstract

We present a detail study of the effect of excess metal atoms on the magnetic properties of Cu 1+ x Cr 2+ y Te 4 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 χ ac 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 2.9 μ B across all the compositions and it reduces with temperature as M( T)∼ A 0 T 3/2+ A 1 T 5/2, as expected for the excitation of Bloch's spin waves in a model of the Heisenberg ferromagnet. Our terminal composition Cu 1.9Cr 2.25Te 4 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.