Magnetic interactions in spin-glasslike Ge1-x-ySnxMnyTe dilute magnetic semiconductors

We investigated the nature of the magnetic phase transition in Ge1-x-ySnxMnyTe mixed crystals with chemical composition changing in the range of 0.083 <= x <= 0.142 and 0.012 <= y <= 0.119. The dc magnetization measurements performed in magnetic fields up to 90 kOe and temperature range 2-200 K showed that the magnetic ordering at temperatures below T = 50 K exhibits features characteristic for both spin-glass and ferromagnetic phases. The modified Sherrington-Southern model was applied to explain the observed transition temperatures. The calculations showed that the spin-glass state is preferred in the range of the experimental carrier concentrations and Mn contents. The value of the Mn hole exchange integral was estimated to be J(pd) = 0.45 +/- 0.05 eV. The experimental magnetization vs temperature curves were reproduced satisfactorily using the noninteracting spin-wave theory with the exchange constant Jpd values consistent with those calculated using modified Sherrington-Southern model. The magnetization vs magnetic field curves showed nonsaturating behavior at magnetic fields B < 90 kOe indicating the presence of strong magnetic frustration in the system. The experimental results were reproduced theoretically with good accuracy using the molecular-field-approximation-based model of a disordered ferromagnet with long-range Ruderman-Kittel-Kasuya-Yosida interaction.