Abstract
Formation of L10-oredered structure from disordered A1 phase has been investigated for FePt and FePd films on MgO(001) substrates employing a two-step method consisting of low temperature deposition at 200 °C followed by high-temperature annealing at 600 °C. L10-(001) variant crystal with the c-axis perpendicular to the substrate grows preferentially in FePd films whereas L10-(100), (010) variants tend to be mixed with the L10-(001) variant in FePt films. The structure analysis by X-ray diffraction indicates that a difference in A1 lattice strain is the influential factor that determines the resulting L10-variant structure in ordered thin films. Misfit dislocations and anti-phase boundaries are observed in high-resolution transmission electron micrographs of 10 nm-thick Fe(Pt, Pd) film consisting of L10-(001) variants which are formed through atomic diffusion at 600 °C in a laterally strained FePt/PeFd epitaxial thin film. Based on the experimental results, a nucleation and growth model for explaining L10-variant formation is proposed, which suggests a possibility in tailoring the L10 variant structure in ordered magnetic thin films by controlling the alloy composition, the layer structure, and the substrate material.
Highlights
Epitaxial FePt and FePd alloy thin films with L10-ordered structure have been investigated for high density magnetic recording media and magnetic random access memory applications due to their large magnetocrystalline anisotropy energies,[1] which assure high thermal stability of magnetization against thermal fluctuation in a very small volume of less than 10 nm in diameter
A set of X-ray diffraction (XRD) data was obtained for FePd films which were reported in our previous paper.[10]
The variation in volume ratio of L10 variant as a function of film thickness clearly indicates that L10(001) crystal with the c-axis perpendicular to the substrate surface nucleates preferentially in FePd film, whereas L10(100), (010) variants tend to be included in FePt film in thinner regions
Summary
Epitaxial FePt and FePd alloy thin films with L10-ordered structure have been investigated for high density magnetic recording media and magnetic random access memory applications due to their large magnetocrystalline anisotropy energies,[1] which assure high thermal stability of magnetization against thermal fluctuation in a very small volume of less than 10 nm in diameter. The L10-ordered structure consists of alternate stacking of Fe and Pt(Pd) atoms along the c-axis of fcc structure. The c/a ratio of ordered structure in balk sample is nearly similar to be 0.96 for the ordered FePt and the ordered FePd materials.[2,3] Film deposition at substrate temperatures typically higher than 500 ◦C is required for L10-ordering, while the structure is disordered fcc (A1) when deposited at lower temperatures. Two-type of L10 crystals with the c-axis orthogonal each other, L10(001) crystal with the c-axis perpendicular and L10(100), (010) crystals with the c-axis lying in-plane with respect to the substrate surface, tend to coexist in epitaxial thin films prepared on oxide single crystal substrates.[4,5,6,7] Such L10 variant crystals with the c-axis lying in-plane and perpendicular to the substrates are observed in the granular thin films prepared on (001) textured polycrystalline
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