Magnetic characterization of thin Co50Fe50 films by magnetooptic Kerr effect

Abstract

Magnetic properties of thin Co50Fe50 films on MgO(0 0 1) prepared with different annealing temperatures between room temperature and 300 degrees C are studied by vectorial magnetometry based on the magnetooptic Kerr effect. Independent from the annealing, the Co50Fe50 films reveal some similar magnetic properties, e. g. no quadratic magnetooptic Kerr effect and a magnetic reversal process which is completely in-plane with magnetic easy axes in Co50Fe50 < 1 1 0 > directions. If the alignment of the external magnetic field is close to the magnetic hard axes, incoherent rotation of magnetic moments between saturation and remanence occurs instead of coherent rotation as for the other directions. If the magnitude of the magnetization is polar plotted with respect to the azimuthal magnetization angle, sequential switching of magnetic moments from one magnetic easy axis to another can be proved by the course of the magnetization. Here, a two-domain switching process can be distinguished from a four-domain switching process generated by the incoherent rotation between saturation and remanence. Furthermore, both the uniaxial magnetic anisotropy constants and the domain wall pinning energies are determined from the magnetic switching fields using the Stoner-Wohlfarth model while the cubic magnetic anisotropy constants are obtained from fitting the magnetization curves. The domain wall pinning energies obtained from these analyses decrease with increasing annealing temperature due to fewer defects in the film. The cubic magnetic anisotropy also decreases slightly which can be attributed to relaxation of the crystal lattice for increasing annealing temperature due to a small change of spin-orbit coupling. Compared with the cubic magnetic anisotropy the uniaxial magnetic anisotropy is very small. This may be attributed to the reduction of strain in the film caused by a buffer stack Cr/Au/Cr between the Co50Fe50 film and MgO(0 0 1).