Magnetic Properties of an Amorphous Mn-P-C Alloy

The magnetic properties of an amorphous ${\mathrm{Mn}}_{75}$ ${\mathrm{P}}_{15}$ ${\mathrm{C}}_{10}$ alloy obtained by rapid quenching from the liquid state and those of the crystalline alloy of the same composition have been measured. The results are interpreted by assuming that the amorphous alloy consists of three different regions mixed randomly (called phases for simplicity) in which the local atomic arrangements are different. Both magnetic and x-ray analyses indicate that one of these phases has a local order based on crystalline ${\mathrm{Mn}}_3$P. One of the remaining phases could have a local order of a ${\mathrm{Mn}}_5$ ${\mathrm{C}}_2$ type, but the other phase cannot be described in detail. Evidence is shown that the antiferromagnetic Néel temperature of an amorphous alloy is reduced to about ½ of that of the corresponding crystalline alloy. By using molecular-field analysis, present results show that the magnetic interactions are less localized to the first-nearest neighbors in the amorphous ${\mathrm{Mn}}_3$P phase than in the crystalline phase.