Specific heat and magnetic susceptibility of single-crystalline ZnCr2Se4 spinels doped with Ga, In and Ce

The crystal structure, X-ray photoelectron spectra (XPS), dc magnetic isotherm, ac magnetic susceptibility and specific heat measurements for antiferromagnetic and semiconducting ZnCr2Se4 spinel diluted with Ga, In and Ce are presented. For all the studied spinels the XPS spectra exhibit the Cr 2p3/2 splitting of 1 eV characteristic for the 3d3 electron configuration of the chromium ions. A correlation between the second critical field Hc2 of the helix to paramagnetic transition and the magnetic specific heat C-peak was found in (Zn0.86Ce0.08)[Cr2]Se4. This correlation weakens for (Zn0.99)[Cr1.92Ga0.06]Se4 and disappears for (Zn0.83In0.11)[Cr1.73In0.14]Se4 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 TN 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, Sm = R ln(2S + 1). These effects are considered within the cation–anion distances in octahedral sites, the cation deficiency and the spin state of 3d Cr3+ ions in t2g orbital.

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► Ga, In and Ce substitutions do not affect the Cr3+ 3d3 electronic configuration.
► The larger interatomic elongations, the lower saturation magnetic moment.
► Imaginary part of susceptibility reveals energy loss only in case of the HS state.
► In the LS state the second critical field is completely quenched.
► The spin wave propagation and lattice contribution weaken with increasing ionic radius.