Magnetic and specific heat properties of a new Gd-doped ZnCr2Se4

The series of chromium selenides Gd-doped ZnCr2Se4 (from 0.07 Gd to 0.21 Gd) was synthesized in polycrystalline form using ceramic method from stoichiometric amounts of elements. The phase and structure determination by X-ray diffraction showed the main cubic normal spinel structure and traces amount of phases ZnSe and the selenium. Magnetic measurements showed an antiferromagnetic order for all compositions with the Neél temperature TN∼22 K, a change of slope at the first critical field Hc1 of about 11.5 kOe for T = 2 K characteristic for a metamagnetic transition, a breakdown of the helical spin arrangement at the second critical field Hc2 of about 60 kOe for T = 2 K, and splitting of the zero-field-cooling and field-cooling susceptibilities below the freezing temperature Tf = 7.3 K suggesting magnetic frustration. Specific heat measurements exhibited first-order anomalies at TN. These effects are interpreted in terms of the superexchange integrals for the first two coordination spheres including structural defects and non-stoichiometry.