Thickness dependence of coercivity in Co-Ni thin films

The magnetic properties and microstructure of sputtered Co80Ni20 thin films with a thickness in the range of 400–3800 Å have been studied using SQUID magnetometry, x-ray diffraction and transmission electron microscopy (TEM). Both the electron and x-ray diffraction results show that all the films have an hcp structure. As the film thickness decreases the grain size decreases and the c axis is inclined to the film plane. The intrinsic coercivity decreases as the thickness increases when the applied field is parallel to the film plane. The dependence of coercivity on the angle θ between the field direction and the normal to the film plane indicates that the coercivity is due to domain wall pinning. The domain wall structure and pinning force play a major role in the thickness dependence of coercivity for films with thickness D<1000 Å.