Specific heat and magnetic susceptibility ofCd1−xMnxSeat low temperature

Abstract

For the insulating ${\mathrm{Cd}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{Se}$ single crystals with composition $x$ between 0.005 and 0.5, the specific heat was measured between 0.5 and 50 K, and the low-field susceptibility between 4 and 50 K. The samples with $x\ensuremath{\ge}0.2$ show a spin-glass transition at low temperature. The phase diagram for the boundary of the paramagnetic and spin-glass region is presented. The excess specific heat in zero magnetic field of all the paramagnetic samples shows a pronounced maximum at \ensuremath{\sim}0.3 K and a broad shoulder at \ensuremath{\sim}0.9 K. This sharp maximum is the consequence of single Mn ions for which the crystal field has removed part of the sixfold degeneracy of the lowest $^{6}S_{\frac{5}{2}}$ state. To produce a maximum in the specific heat at 0.3 K, the energy-level splitting needed is about 50 times larger than the splitting found by EPR measurements for samples with much lower Mn concentration. It is speculated that this splitting is a consequence of stresses in the crystal lattice caused by substitution of smaller Mn ions for larger Cd. The broad shoulder is a consequence of ions which are paired and have a Heisenberg exchange energy $J=\ensuremath{-}1.75$ K.