Fabrication and characterization of L10-ordered FeNi thin films

解説・概説記事

L10-ordered FeNi, showing high uniaxial magnetic anisotropy (Ku), is promising as a “raremetal-free” high Ku material. We have worked on L10-ordered FeNi thin films prepared by twomethods: one is molecular beam epitaxy (MBE) with alternate deposition of Fe and Nimonatomic layers, and the other is sputtering with co-deposition or multilayer-deposition ofFe and Ni followed by rapid thermal annealing (RTA). For the MBE films prepared by alternatemonatomic 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 bysynchrotron x-ray diffraction (XRD) was found with maximum values of S = 0.48 and Ku = 7.0×106 erg/cm3. The composition dependence of Ku was also investigated by deviating thethickness from monatomic layer, showing a maximum of 9.3×106 erg/cm3 around 60 at.%Fe. Inaddition, the effect of Co addition to L10-ordered FeNi was investigated, suggesting that asmall amount (<10 at.%) of Co substitution for Ni would enhance Ku if S keeps the same. Theexperiments were in qualitatively good agreement with the first-principles calculations. Themagnetic 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 sputteredfilms with RTA, no major difference between co-deposition and multilayer-deposition wasfound: in both cases the formation of L10-ordered phase after RTA was definitely confirmedby XRD. TEM observation indicated that nanometer-sized L10-ordered clusters weredispersed in a disordered phase, in contrast to that of MBE films showing the homogeneousformation of L10-ordered phase. The enhancement of coercivity (Hc) and residualmagnetization (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.