Magnetic Properties of CdCr2Se4
摘要
The dependence of magnetization, δ, and resistivity, ρ, on temperature T and magnetic field H has been studies near Curie point and at somewhat higher temperatures for single crystals of CdCr2Se4 deficient in selenium or doped with indium or copper. The magnetic field has a pronounced effect on the Tc values determined by extrapolation of the steepest section of the δ (T)‐ curves to the temperature axis. Thus, an increase of the field strength from 0.9 to 12.7 kOe leads to a 20 to 30° high temperature shift of the Curie point. The δ (H) curves measured near Tc are characterized by critical field values in the vicinity of which magnetization increases stepwise by about 80%. Copper doped crystals exhibit thermomagnetic hysteresis and those containing indium show positive magnetic resistivity in the temperature region where the critical field phenomena are observed. The experimental data are explained by the formation of ferrons, that is ferromagnetic microregions, under the action of magnetic field. The f erroas which owe their stability to the s‐d exchange and Coulomb attraction are supposed to be localized at non‐ionized impurity atoms. The magnetic field induced transition from a paramagnetic state to that characterized by the presence of ferrons represents the first‐order phase transition.