L 1 1 type Co-Pt ordered alloy films with a large uniaxial magnetic anisotropy, Ku, of the order of 107erg∕cm3 were successfully fabricated at relatively low substrate temperatures of 270–390°C using ultrahigh vacuum sputter film deposition. L11 type ordered Co-Pt films, with the ⟨111⟩ direction (easy axis of magnetization) perpendicular to the film plane, were fabricated on MgO(111) single crystal substrates and glass disks. The ordered structure was formed in a wide Pt content region of 40–75at.%, and Ku showed a maximum at around 50at.% Pt content. The values of the order parameter S and Ku for L11 type Co50Pt50 films increased as the substrate temperature Ts, increased. Ku reached about 3.7×107erg∕cm3 (S=0.54) at Ts=360°C for the single crystal films deposited on MgO(111) substrates, indicating a potential increase in Ku by enhancing the ordering. The values of Ku for polycrystalline films deposited on glass disks were smaller than those for the single crystal films on MgO(111) substrates, however, Ku reached 1.9×107erg∕cm3 at Ts=360°C. The experimental results demonstrate the potential of L11 type Co50Pt50 films for use in data storage applications, because of their very high Ku, comparable to L10 type Fe50Pt50 films, the relatively low fabrication temperature, and good controllability of the grain orientation.

The perpendicular magnetic anisotropy of CoPtCr films deposited on Ru seed layers is discussed as a function of film composition. Moreover, the change in by the addition of SiO 2 is examined in light of thermal stability of CoPtCr-SiO 2 media. The of Co-10 at % Cr shows a high value of 5 10 6 erg cm 3 , which is much higher than that reported by Bolzoni et al. The addition of Pt to the Co-10 at % Cr film results in a further enhancement of . A maximum of nearly 10 10 6 erg cm 3 is observed at 25 30 at % Pt. All series of films with various Cr contents show maximum values of at 25 30 at % Pt. The maximum value for CoPt (Cr = 0) films reaches 15 10 6 erg cm 3 . The value of magnetocrystalline anisotropy of grains, calculated by taking account of the volume fraction of CoPtCr grains, decreases as the SiO 2 content increases. However, the maintains a large value of more than 7 10 6 erg cm 3 , even at 10 at % SiO 2 in addition to (Co 90 Cr 10 ) 80 Pt 20 , which indicates a high potential of CoPtCr-SiO 2 media to resist thermal agitation of magnetization.Index Terms-CoPtCr films, CoPtCr-SiO 2 media, perpendicular magnetic anisotropy, Ru seed layer, thermal agitation of magnetization.

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In this study, we have experimentally investigated the microwave assisted magnetization by switching (MAS) on the microstructured Co/Pt multilayer. The sample exhibits the typical magnetization curve peculiar to perpendicular anisotropy films, that is, a steep reversal initiated by nucleation of a reversed domain followed by its subsequent gradual expansion by the domain wall displacement. By applying microwaves with the frequency of GHz order, the nucleation field Hn is significantly reduced at three frequencies. Taking into account the effective anisotropy field of our sample, the first dip of Hn at the lowest frequency probably corresponds to the Kittel mode excitation, and the other two dips at higher frequencies correspond to unidentified excitation modes other than the Kittel mode. Among them, the last dip of Hn at the highest frequency reaches about 1/3 of that without microwave application. These results suggest the existence of more effective excitation modes for MAS than the Kittel mode.

A large uniaxial magnetic anisotropy Ku of about 2×107erg∕cm3 was obtained in Co–(20–30) at. % Pt perpendicular films deposited on Ru seed layers. The films showed good c-axis orientation perpendicular to the film plane, and no evidence of a Co3Pt-type-ordered structure was found in the X-ray-diffraction patterns. The value of Ku (the sum of the first- and second-order terms of uniaxial anisotropy, Ku1 and Ku2) increased as the thickness of the CoPt layer decreased, and reached about 2×107erg∕cm3 at 2 nm (Co–20 at. % Pt films) or 5 nm (Co–(25–30) at. % Pt films). The ratio of Ku2 to Ku1 was 0.16 in 40 nm films, but reduced to less than 0.03 for thicknesses below 5 nm. The experimental results suggest that, besides the surface anisotropy, the increase in Ku on reducing the thickness is mostly related to the reduction of the hcp-CoPt lattice c∕a ratio, probably due to epitaxial growth of CoPt on the Ru seed layer.