Anomalous magnetic behavior of nanocrystalline Fe TaC films at high temperature

We have studied the magnetic properties of the nanocrystalline Fe79Ta10C11 films with different crystallographical characteristics. The soft magnetic properties are not related to the Fe characteristics but closely related to the TaC characteristics, such as the lattice parameter and grain size. The film composed of fine TaC grain with small lattice parameter has excellent soft magnetic characteristics at room temperature and its magnetic properties little change with temperature. On the contrary, the film composed of large TaC grain with large lattice parameter has large coercive force and magnetostriction at room temperature and shows the anomalous magnetic behavior at high temperature; the coercive force at 300 degrees C becomes 10 times larger than that at room temperature. This phenomenon is most likely caused by the disappearance of the intergranular ferromagnetic coupling.