We prepared L10-ordered FeNi alloy films by alternate deposition of Fe and Ni monatomic layers, and investigated their magnetic anisotropy. We employed a non-ferromagnetic Au-Cu-Ni buffer layer with a flat surface and good lattice matching to L10-FeNi. An L10-FeNi film grown on Au6Cu51Ni43 showed a large uniaxial magnetic anisotropy energy (Ku = 7.0 × 10(6) erg cm(-)3). Ku monotonically increased with the long-range order parameter (S) of the L10 phase. We investigated the Fe-Ni composition dependence by alternating the deposition of Fe 1 − x and Ni 1 + x monatomic layers (− 0.4 < x < 0.4). Saturation magnetization (Ms) and Ku showed maxima (Ms = 1470 emu cm(-3), Ku = 9.3 × 10(6) erg cm(-3)) for Fe60Ni40 (x = -0.2) while S showed a maximum at the stoichiometric composition (x = 0). The change in the ratio of lattice parameters (c/a) was small for all compositions. We found that enrichment of Fe is very effective to enhance Ku. The large Ms and Ku of Fe60Ni40 indicate that Fe-rich L10-FeNi is promising as a rare-earth-free permanent magnet.
Highly L10-ordered FePt thin films with a strong (001) texture were successfully fabricated on amorphous substrates simply by co-sputtering and rapid thermal annealing at a low temperature of 400 °C. The morphology of FePt thin films depended strongly on the heating rate, changing from a continuous structure with an atomically flat surface to an island-like structure. The change of the morphology resulted in a drastic increase of coercivity, indicating that the magnetization process could be controlled by the heating condition. This fabrication method of ordered FePt thin films is favorable in view of the compatibility for a practical device fabrication process
L10-ordered FeNi, showing high uniaxial magnetic anisotropy (Ku), is promising as a ‘rare metal-free’ high Ku material. We have worked on L10-ordered FeNi thin films prepared by two methods: one is molecular beam epitaxy (MBE) with alternate deposition of Fe and Ni monatomic layers, and the other is sputtering with co-deposition or multilayer-deposition of Fe and Ni followed by rapid thermal annealing (RTA). For the MBE films prepared by alternate monatomic layer deposition (leading to the stoichiometric composition: Fe 50 at.%– Ni 50 at.%), a clear relationship between Ku and the long-range order parameter S estimated by synchrotron x-ray diffraction (XRD) was found with maximum values of S = 0.48 and Ku = 7.0 × 106 erg cm−3. The composition dependence of Ku was also investigated by deviating the thickness from monatomic layer, showing a maximum of 9.3 × 106 erg cm−3 around 60 at.%Fe. In addition, the effect of Co addition to L10-ordered FeNi was investigated, suggesting that a small amount (<10 at.%) of Co substitution for Ni would enhance Ku if S keeps the same. The experiments were in qualitatively good agreement with the first-principles calculations. The magnetic damping constant α was also measured to be approximately 0.01 irrespective of S, suggesting that L10-FeNi is a candidate material with high Ku and low α. For the sputtered films with RTA, no major difference between co-deposition and multilayer-deposition was found: in both cases the formation of L10-ordered phase after RTA was definitely confirmed by XRD. Transmission electron microscopy observations indicated that nanometer-sized L10-ordered clusters were dispersed in a disordered phase, in contrast to that of MBE films showing the homogeneous formation of L10-ordered phase. The enhancement of coercivity (Hc) and residual magnetization (Mr/Ms) was observed associated with the appearance of L10-ordered phase. The maxima of Hc and Mr/Ms were obtained to be 1.35 kOe and 0.22, respectively.
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