Fabrication and characterization of <i>L</i> 1 ₀ -ordered FeNi thin films

Abstract L 1 0 -ordered FeNi, showing high uniaxial magnetic anisotropy ( K u ), is promising as a ‘rare metal-free’ high K u material. We have worked on L 1 0 -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 K u and the long-range order parameter S estimated by synchrotron x-ray diffraction (XRD) was found with maximum values of S = 0.48 and K u = 7.0 × 10 6 erg cm −3 . The composition dependence of K u was also investigated by deviating the thickness from monatomic layer, showing a maximum of 9.3 × 10 6 erg cm −3 around 60 at.%Fe. In addition, the effect of Co addition to L 1 0 -ordered FeNi was investigated, suggesting that a small amount (&lt;10 at.%) of Co substitution for Ni would enhance K u 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 L 1 0 -FeNi is a candidate material with high K u 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 L 1 0 -ordered phase after RTA was definitely confirmed by XRD. Transmission electron microscopy observations indicated that nanometer-sized L 1 0 -ordered clusters were dispersed in a disordered phase, in contrast to that of MBE films showing the homogeneous formation of L 1 0 -ordered phase. The enhancement of coercivity ( H c ) and residual magnetization ( M r / M s ) was observed associated with the appearance of L 1 0 -ordered phase. The maxima of H c and M r / M s were obtained to be 1.35 kOe and 0.22, respectively.