Magnetic interactions in spin-glasslikeGe1−x−ySnxMnyTedilute magnetic semiconductors

Abstract

We investigated the nature of the magnetic phase transition in ${\text{Ge}}_{1\ensuremath{-}x\ensuremath{-}y}{\text{Sn}}_{x}{\text{Mn}}_{y}\text{Te}$ mixed crystals with chemical composition changing in the range of $0.083\ensuremath{\le}x\ensuremath{\le}0.142$ and $0.012\ensuremath{\le}y\ensuremath{\le}0.119$. 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 $T=50\text{ }\text{K}$ 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 ${J}_{pd}=0.45\ifmmode\pm\else\textpm\fi{}0.05\text{ }\text{eV}$. The experimental magnetization vs temperature curves were reproduced satisfactorily using the noninteracting spin-wave theory with the exchange constant ${J}_{pd}$ values consistent with those calculated using modified Sherrington-Southern model. The magnetization vs magnetic field curves showed nonsaturating behavior at magnetic fields $B<90\text{ }\text{kOe}$ 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.