The structural and magnetic properties of Co-based multilayer thin films were studied to utilize these materials and especially, the exchange coupling in double layer systems consisting of the memory and reference layers of e-beam evaporated Co-based multilayer thin films were investigated.
The effects of deposition angle on the structural and magnetic properties of e-beam evaporated Co/Pt multilayer thin films were examined. It was found that the [111] crystallographic orientations of multilayer thin films were not aligned with columnar growth orientations and they were remained to be normal to the substrate planes, irrespective of deposition angle, even though the deposition angle was severely oblique up to 60°. Interestingly enough, the magnetic easy axis orientation was nearly aligned with the substrate normal irrespective of deposition angle, which suggested that the surface anisotropy was a major origin of the perpendicular anisotropy in Co/Pt multilayer thin films.
The magnetic property in Co-based multilayer thin films was dependent on the thicknesses of Co and Pd (or Pt). It was found that Co-based multilayer thin films had perpendicular magnetic anisotropy for the Co-sublayer thickness of Co, 4 Å and Pd (or Pt) sublayer ≥9Å. Since the squareness of hysteresis loop was deteriorated with decreasing the Co-sublayer thickness, it was chosen that $(2-Å Co/9.2-Å Pd)_23$ was used as the memory layer and the reference layer $(4-Å Co/9.2-Å Pd)_23$ $(or (3-Å Co/8.8-Å Pd)_13)$ due to its high and low coercivity, respectively.
Using the characteristic matrix, the dependences of magneto-optical effects on the layer thickness in bilayer, trilayer, and quadrilayer structures were theoretically investigated to maximize the figure-of-merit (FOM) at the wavelength of 458 and 830 nm. It was found that the quadrilayer structure yields more than one and half fold enhancement in the FOM, compared with the bilayer structure at both wavelengths. And the FOM at the wavelength of 458 nm was found to be two and half times larger than one at the wavelength of 830 nm having the same layer structure.
We have studied the exchange coupling in double layer systems consisting of the memory and reference layers of e-beam evaporated Co-based multilayer thin films. The structure of the specimens was examined by x-ray diffractometer and the magnetic and magneto-optic properties were measured by vibrating sample magnetometer and Kerr spectrometer, respectively. X-ray diffractometry revealed that all of the specimens had multilayer structure. The exchange coupling in the double layer system was so strong that the magnetization reversal of one layer was occurred simultaneously with that of the other. The strength of the exchange coupling was dependent on the thickness of a non-magnetic spacer between the memory layer and the reference layer. It was found that exchange coupling was decreased when the spacer was thicker than about 50Å. The existence of exchange coupling was also confirmed by domain writing experiment.
