Tuning the Perpendicular Magnetic Anisotropy of Co-Based Layers in Multilayered Systems

The combination of Pt with Co either in alloy or in multilayer form is widely studied among the potential magnetic media for ultrahigh density magnetic recording. On the other hand the combination of Co with Cr in alloy form is currently providing commercial magnetic media. In an effort to further exploit and benefit from both systems, we fabricated Co_1−x Cr _x /Pt multilayers with two adjustable parameters. The first one is the Cr concentration on CoCr layer (x = 0, 5, 30), which modulates segregation effects on Co grains, thus tunes macroscopic magnetic features such as saturation magnetization and coercive field. The second one is the small layer thickness (≤0.6 nm) that affects interlayer coupling, perpendicular magnetic anisotropy and magnetization enhancement through spin polarization of Pt atoms in a ferromagnetic environment. The X-ray diffraction patterns verified the existence of multilayered structures following a preferable face-centered-cubic stacking. The Pt thickness and Cr concentration are found to significantly affect the macroscopic magnetic behavior. It is remarkable the fact that, samples present perpendicular anisotropy that scales with Pt thickness and temperature, even in the case of significant Cr concentration (30% in the alloy) when ferromagnetic behavior is expected to diminish according to relevant studies in alloys and in bulk films. Such an effect may be attributed to spin-polarization of Pt interlayers and was evidenced by X-ray magnetic circular dichroism. The spin-polarization of Pt is also the drive for the strong magneto-optic enhancement in the ultra-violet region between 4.5 and 5 eV shown by magneto-optic Kerr spectroscopy.