Anomalous magnetic behaviour of nanocrystalline FeTaC films at high temperature

The magnetic properties of nanocrystalline Fe/sub 79/Ta/sub 10/C/sub 11/ films with different crystallographic characteristics are studied. The soft magnetic properties are not related to the Fe characteristics, but are closely related to the TaC characteristics, such as the lattice parameter and grain size. The film, composed of fine TaC grain with a small lattice parameter, has excellent soft magnetic characteristics at room temperature and its magnetic properties change little with temperature. On the contrary, the film composed of large TaC grain with a large lattice parameter has a large coercive force and magnetostriction at room temperature and exhibits a anomalous magnetic behavior at high temperature. The coercive force at 300 degrees C becomes ten times larger than that at room temperature. This phenomenon is most likely caused by the disappearance of the intergranular ferromagnetic coupling.>