High pressure synthesis and magnetic properties of cubic B20 MnGe and CoGe

摘要

Samples of MnGe and CoGe having cubic B20 structure were prepared at high pressure. Magnetic measurements showed that CoGe is a Pauli paramagnet, but MnGe exhibits antiferromagnetic-type ordering below T _N = 175 K. The magnetic susceptibility of MnGe follows a Curie-Weiss law above 300 K with an effective magnetic moment μ _(eff) = 3.68 μ _B/f.u. and θ _p = + 231 K. The large positive value of θ _p indicates a strong ferromagnetic exchange. The value of the effective moment is close to the free Mn ~(4+) ion (~4F _(3/2)) value 3.87 μ _B/f.u. From measurements of the magnetization of MnGe in fields up to 60 kOe and in the temperature range 2-350 K, we constructed its T-H magnetic phase diagram which is similar to that proposed for MnSi-type compounds with helical magnetic order. Specific heat measurements reveal that the total magnetic entropy of MnGe relative to nonmagnetic CoGe is equal to 3.55 J/mole-K (0.62Rln2).