Effect of Pressure on the Ferromagnetic Transition ofMnAsxSb1−xSolid Solutions

The ferromagnetic transition temperatures of $\mathrm{Mn}{\mathrm{As}}_x{\mathrm{Sb}}_{1-x}$ solid solutions for $0\le x\le 1$ have been measured as a function of pressure up to 4.5 kbar. Previous work has shown that for the solid solutions in the concentration range $0.9\lesssim x\le 1$ the magnetic transition is first order and is accompanied by a hexagonal-to-orthorhombic structure transformation, while for $0\le x\lesssim 0.9$ the magnetic transition is second order with no structural change. We have found that the initial pressure derivative of the transition temperature ($\frac{\partial T_c}{\partial P}$) changes discontinuously in the narrow concentration range $0.87\lesssim x\le 0.90$, further demarcating the first- and second-order regions. We also find that substituting Sb for As in the first-order region increases the critical pressure $P_c$ which stabilizes the orthorhombic phase to the lowest temperature. This further supports Goodenough's observation of a critical molar-volume range in which the first-order transformation occurs. The solid solutions which exhibit second-order behavior are analyzed using an itinerant-electron ferromagnet model.