Induced magnetic anisotropy in amorphous Fe24Co68Zr8 thin films

Amorphous building blocks, due to their uniformity, are good candidates for TMR (tunnelling magnetoresistance) structures, for which the tailoring of magnetic anisotropy is a valuable aspect. Amorphous thin films Al/AlZr/Fe24Co68Zr8(10 nm)/AlZr/Si and Al/AlZr/[Fe24Co68Zr8(3 nm)/AlZr(3 nm)]2/Si were grown using dc magnetron sputtering in the presence of an external magnetic field (growth field). The two magnetic layers of the latter sample were deposited in different directions of the growth field rotated by 90 to each other. By means of ferromagnetic resonance (FMR), a uniaxial anisotropy with the hard axis along the direction of the growth field was found in the single layer sample. The FMR spectra of the bi-layer reveal the superposition of 2 sets of angular dependences shifted by 90 to each other, indicating that the growth field has imprinted layer specific anisotropy in different layers. The temperature dependences of effective magnetization and uniaxial anisotropy have been evaluated from low-temperature FMR. The hysteresis loops of the single layer sample measured by SQUID show exchange bias which decreases with increasing temperature, suggesting the presence of an antiferromagnetic phase in the sample.