Magnetization and magnetic susceptibility of the diluted magnetic semiconductors Zn1−xCoxS and Zn1−xCoxSe

Abstract

Magnetization measurements have been done at 1.5 K and magnetic fields up to 7 T by using extraction method on the samples with x=0.0055, 0.048, 0.063 for Zn1−xCoxS and x=0.0097, 0.030, 0.037, 0.042 for Zn1−xCoxSe. In both Co-based systems, the magnetization increases with x. A modified Brillouin function fits the data and the fitting parameters T0( ≳ 0) and Seff are obtained. These results reflect that there exists a strong antiferromagnetic interaction among Co++ ions and the antiferromagnetic interaction in Zn1−xCoxSe is stronger than that in Zn1−xCoxS. Magnetic susceptibility was measured in the temperature range 1.5 K≤T≤300 K by using a vibrating-sample magnetometer. The susceptibility displays a high-temperature Curie–Weiss behavior. From quantitative analysis we obtain the nearest-neighbor Co++–Co++ exchange integral constant J1/kB for sulfides and selenides to be −51±6 K and −57±8 K, respectively. This value is at least three times as large as that in their Mn-based counterparts, and we confirm that the antiferromagnetic interaction is stronger in Zn1−xCoxSe than in Zn1−xCoxS. By using our results in conjunction with a direct measurement of the nearest-neighbor exchange JNN from recent inelastic neutron scattering for Zn1−xCoxS, we obtain an estimate of the next-nearest-neighbor exchange constant J2/kB = −8 K.