Complex magnetic phase diagram of metamagnetic MnPtSi.

The magnetic, thermal and transport properties as well as electronic band structure of MnPtSi are reported. MnPtSi is a metal that undergoes a ferromagnetic transition at T_C = 340(1) K and a spin–reorientation transition at T_N = 326(1) K to an antiferromagnetic phase. First–principles electronic structure calculations indicate a not–fully polarized spin state of Mn in a d^5 electron configuration with J = S = 3/2, in agreement with the saturation magnetization of 3 µ_B per f.u. in the ordered state and the observed paramagnetic effective moment. A sizeable anomalous Hall effect in the antiferromagnetic phase alongside the computational study suggests that the antiferromagnetic structure is noncollinear. Based on thermodynamic measurements and resistivity data we construct a magnetic phase diagram. Magnetization curves M(H) at low temperatures reveal a metamagnetic transition of spin–flop type. The spin-flopped phase terminates at a critical point with T_cr ≈ 300 K and H_cr ≈ 10 kOe, near which a peak of the magnetocaloric entropy change is observed. Using Arrott plot analysis and magnetoresistivity data we argue that the metamagnetic transition is of a first–order type, whereas the strong field dependence of T_N and the linear relationship of the T_N with M^2 hint at its magnetoelastic nature.