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 ferromagnetic behavior in excess co. in off-stoichiometric alloys the saturation magnetization is lower than in co2mnal, whereas the curie temperature tc is higher in all the studied alloys. tc 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.