Compositionally modulated Co/Pt multilayer thin films have been attracting wide attention because of their novel properties and potential technological applications.
Main goal of this study is to enhance the dynamic properties of Co/Pt magneto-optical disk by optimizing the major static parameters such as the anisotropy, the coercivity, and the Kerr effects in Co/Pt multilayer (ML). To understand major static parameters, we have investigated the dependence of the surface anisotropy in Co-based MLs on the interface roughness. We have studied the etching effects of $Si_3N_4$ underlayer on Co/Pt ML. We have analyzed the major origin of the high coercivity in Co/Pt ML on the $Si_3N_4$ underlayer prepared onto the rotating substrate. We compared the measured and calculated values of the dependence of the Kerr rotation, ellipticity, and reflectivity on the thickness of the antireflection layer. Finally, we have tested Co/Pt magneto-optical disks prepared with the optimized conditions using the results obtained from the studies of the static parameters in the Co/Pt ML. We describe the whole procedure of this work in detail.
We have investigate the effects of interfacial roughness on the surface anisotropy in Co/Pt and Co/Pd ML prepared by sputtering. Degree of interfacial roughness was varied by changing Ar sputtering gas pressure from 2 to 20 mTorr for Co/Pt and 2 to 15 mTorr for Co/Pd MLs. The surface anisotropy was found to be increasing with decreasing interface roughness. We have observed that the surface anisotropy for the ML films prepared at various Ar pressure was logarithmically dependent on the integrated low-angle x-ray intensity. This logarithmic relation between surface anisotropy and integrated low-angle x-ray intensity is found to be universal in Co-based MLs.
The anisotropy of Co/Pt MLs was strongly dependent on the underlayer treatment. We observed perpendicular anisotropy for Co/Pt ML prepared on the etched $Si_3N_4$ underlayer. However, Co/Pt ML prepared on the unetched $Si_3N_4$ underlayer showed In-plane. The increase of the anisotropy in Co/Pt ML on etched underlayer seemed to be caused by the the enhancement of the interface sharpness.
We have found that the coercivity was increased when a Co/Pt ML on a $Si_3N_4$ underlayer was prepared onto a rotating substrate. More than four fold increase in the coercivity is thought to be due to the enhancement of domain wall pinning effects caused by an increase of surface roughness in the $Si_3N_4$ underlayer. According to the results of atomic force microscopy, the surface of the $Si_3N_4$ underlayer prepared onto the rotating substrate was rougher than that of an underlayer prepared onto a stationary substrate. We believe that the enhancement of the surface roughness is due to the oblique incidence of the sputtered materials on the rotating substrate.
Co/Pt ML on dielectric antireflection for optical tunning is useful to maximize the figure-of-merit (FOM). Kerr rotation angle, ellipticity, and reflectivity of bilayer structured samples, consisting of Co/Pt ML and $Si_3N_4$ antireflection layer, were compared with the calculated results. Fairly good fitting was obtained between measured and calculated results for the samples of (5-A Co/9-A Pt) with 9-bilayer ML on the antireflection layer varying thickness of 280-570 A.
Co/Pt disks were prepared and tested using a dynamic tester at 780 nm wavelength. Carrier-to-noise ratio (CNR) was increased with decreasing sputtering Ar pressure in preparation of disks. We have observed that the CNR and the FOM showed a linear relation. The CNR of 44.7 dB at ISO condition and 47.3 dB at 1 MHz frequency were obtained.