Interpretation of the Anomaly in the Magneto-Crystalline Anisotropy Energy of Disordered Fe–Pt Invar Alloys by Using the Itinerant Electron Model

Disordered Fe–Pt Invar alloys (around 30 at% Pt) show anomalous properties in both temperature and magnetic field dependences of the magneto-crystalline anisotropy constant K 1 . A theory has been proposed based on the itinerant electron model by assuming a strong relationship between K 1 and the Fermi level of the minority spin band. The temperature dependence of K 1 can be explained by using the present theory. The decrease of the absolute value of K 1 with increasing the external field can also be explained by the present theory.