Shape of temperature dependence of spontaneous magnetization of various ferromagnets

Abstract

The shape of the temperature dependence of spontaneous magnetization was analyzed for about forty ferromagnetic materials. The squareness of the shape was determined by fitting the magnetization curves with the superellipse equation (Lame curve). The agreement between the Lame curve fits and the experimental data was good for most materials. The squareness parameter (the power coefficient in the superellipse equation was found to range from 1.4 to 3.0. The largest squareness was observed for iron, whereas the smallest was found for antiferromagnetic materials and the Ni55Cu45 alloy. The squareness parameter was studied as a function of the Curie temperature, TC. For metallic alloys, a general tendency was observed: the squareness increased with increasing Curie temperature. The only exception was cobalt, which exhibited the same magnetization curve in reduced coordinates as nickel despite having a Curie temperature twice as high. The addition of either ferromagnetic or nonferromagnetic metals to iron or nickel led to a decrease in squareness. No influence of the thermal expansion coefficient on the magnetization curve was observed: zero-expansion Invar exhibited a standard shape following the Lame curve.