Magnetic transitions at high fields in (Fe,Mn)3Si alloys

In the series of ordered DO3 solid solutions Fe3−xMnxSi, field-induced transitions have previously been found to occur for antiferromagnetic alloys with values of x near 1.70. The present work has determined a region of composition in which antiferromagnetism is the low-field, low-temperature state and gives the variation of the critical field as a function of temperature and composition. The critical field decreases approximately quadratically with temperature and rises to beyond 6 T in the range of composition from 1.6≤x≤1.8. Neutron diffraction indicates that the antiferromagnetic axis is shifted from the [111] direction and that in a 5 T field the antiferromagnetic component of the scattering is reduced considerably from that in zero field. However, no corresponding increase in ferromagnetic component is observed within experimental error and Arrott plots suggest the high-field state is still largely antiferromagnetic.