Magnetic response of Fe_1-xCo_xSi alloys: A detailed study of magnetization and magnetoresistance

Results of dc magnetization and magnetoresistance measurements are presented for the heliferromagnetic Fe_1-xCo_xSi alloys with x=0.35 and 0.45. The field and temperature dependence of the magnetization suggests the presence of Stoner-like excitations in these alloys which in turn indicates significant itinerant character of the ferromagnetic state. Similarities with other weak itinerant electron ferromagnets are pointed out. While the relatively large and unusual positive magnetoresistance in the ferromagnetic state of these alloys has earlier been rationalized in terms of quantum interference effect, magnetism probably plays a role in the magnetoresistance of these alloys near the Curie temperature and even at temperatures well inside the paramagnetic regime.