Specific heat and magnetic susceptibility of single-crystalline ZnCr 2Se 4 spinels doped with Ga, In and Ce

Abstract

The crystal structure, X-ray photoelectron spectra (XPS), dc magnetic isotherm, ac magnetic susceptibility and specific heat measurements for antiferromagnetic and semiconducting ZnCr 2Se 4 spinel diluted with Ga, In and Ce are presented. For all the studied spinels the XPS spectra exhibit the Cr 2 p 3/2 splitting of 1 eV characteristic for the 3 d 3 electron configuration of the chromium ions. A correlation between the second critical field H c2 of the helix to paramagnetic transition and the magnetic specific heat C-peak was found in (Zn 0.86Ce 0.08)[Cr 2]Se 4. This correlation weakens for (Zn 0.99)[Cr 1.92Ga 0.06]Se 4 and disappears for (Zn 0.83In 0.11)[Cr 1.73In 0.14]Se 4 as the saturation magnetic moment rapidly decreases in the sequence Ce, Ga and In. The magnetic contribution to the specific heat displays a sharp peak at T N and is maximal at the spin fluctuation temperature of 40 K, which is related to the maximum of the magnetic susceptibility at the same temperature and at 50 kOe in the spin fluctuation region, evidenced by the entropy exceeding 90% of the entropy calculated classically for the complete alignment of the Cr spins, S m = R ln(2 S + 1). These effects are considered within the cation–anion distances in octahedral sites, the cation deficiency and the spin state of 3 d Cr 3+ ions in t 2g orbital.