Magnetic properties of nanocomposite cobalt-based thin films

The magnetic properties of cobalt clusters embedded in a nonmagnetic matrix were measured. Films with cobalt clusters with an average diameter of 5.5 nm embedded both in Cu and Ag are reported on. Volumetric concentrations of Co ranged from 10% to 50%. Magnetization and low temperature hysteresis loops, both field cooled and zero field cooled have been measured between 4.2 and 300 K. The field cooled and zero field cooled magnetization bifurcate at or above room temperature with the clusters having a nonzero remanence at room temperature. Low temperature hysteresis loops exhibit a two-phase nature with one phase displaying exchange bias, suggesting the presence of an oxide phase. The effects of placing Co/Pt bilayers on dysprosium-iron-gamet doped with bismuth and aluminum have been studied. The garnet was deposited by RF-magnetron sputtering and crystallized by rapid thermal annealing. The Co/Pt bilayers were then deposited by DC-magnetron sputtering. The garnet thickness was held constant at 1000Å while the Co/Pt bilayers had the form of [3ÅCo/9ÅPt]n with n ranging from 1 to 16. Coercivities of the samples ranged from about 300 to 2000 Oe. Kerr rotations were as high as 1.8° and ellipticities up to 2° depending upon the wavelength of light and the number of Co/Pt bilayers. Co/Pt multilayers were DC-magnetron sputtered at argon pressures ranging from 5 to 20 mTorr. Again, the structure of the multilayers was [3ÅCo/9ÅPt]n where n ranged from 6 to 24. The temperature dependence of the magnetic properties, magnetic reversal, and thermal stability of these films have been studied by magneto-optics and compared to several energy barrier theories. The 14 mTorr samples are consistent with a Stoner-Wohlfarth type energy barrier, while the 5 mTorr samples are more consistent with a 1/H type energy barrier