Control of magnetization reversal and domain structure in (Co/Ni) multilayers

We present a study of the magnetic properties of [Co(0.3 nm)/Ni(0.6 nm)]_×N multilayers as a function of bilayer repetitions N. From magnetometery measurements, magnetic force microscopy (MFM) and X-ray diffraction (XRD), a correlation between the magnetic and structural properties could be made. It is shown that the multilayers exhibit square hysteresis loops for N ≤ 8 with a maximum coercivity of about 220 Oe for N = 8. The XRD scan and rocking curve measurements reveal that fcc phase of (Co/Ni) is improved for a larger value of N. Micromagnetic simulation is conducted on each multilayer at demagnetized state to reproduce the MFM images. From the best correspondence of the experimental and simulated domain structures, intrinsic parameters such as saturation magnetization M_s anisotropy energy K_u and average domain size were obtained. It is found that M_s value of all the multilayers is about 800 emu/cm³ with less than 3% difference. On the other hand, K_u shows a continuous decrease with N down to 12% from its largest value for 4 bilayers.