Magnetic properties of Co1−xFexSi, Co1−xMnxSi, and Fe1−xMnxSi solid solutions

Thermomagnetic measurements have been made on Co1—xFexSi, Co1—xMnxSi, and Fe1—xMnxSi solid solutions with the B20 structure. The Co1—xFexSi solid solutions in the composition range 0.30 ≦ x ≦ 0.80 are ferromagnetic at low temperatures with a magnetic moment per Fe atom of 0.25 μB at most, which is smaller than the value obtained in the paramagnetic region. These magnetic properties of the Co1—xFexSi solid solutions may be interpreted in terms of a collective electron model. No magnetically ordered region was observed in the Co1—xMnxSi solid solutions; all the solid solutions show paramagnetic behaviour. The effective moment per Mn atom is nearly constant in the composition range 0.10 ≦ x ≦ 0.90 and equal to the value for MnSi. The dilute solid solutions show relatively large effective moments. The temperature dependence of the susceptibility of the Fe1—xMnxSi changes with composition in a complicated way. The magnetic properties of both Co1—xMnxSi and Fe1—xMnxSi cannot be described in terms of a simple localized model.