Structural and magnetic properties of the half-ferromagnetic CO2+x+yMn1-xAl1-y alloys

CO2+x+yMn1-xAl1-y intermetallic compounds have been prepared by arc melting and studied with X-ray diffraction and magnetization measurements to ascertain the effect of deviations of composition from the stoichiometry on the ferromagnetism of this system. Hysteresis loops registered at room temperature show a soft ferromagrictic behavior in excess Co. In off-stoichiometric alloys the saturation magnetization is lower than in CO2MnAl, whereas the Curie temperature T-C is higher in all the studied alloys. T-C varies substantially with variations in composition and increases with the Mn content. In the source of this behavior a volume effect is inferred which is expected to lead to strengthened ferromagnetic exchanges.