Fe–Ni composition dependence of magnetic anisotropy in artificially fabricated L1₀-ordered FeNi films

Abstract

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.

Intrinsic magnetic properties of L1 FeNi obtained from meteorite NWA 6259

“…15 Together these data yield an anisotropy constant K ¼ 0.84 MJ/m 3 . This value falls into the range of K values reported by Kojima et al 7 for artificially grown ordered FeNi films of different Fe/Ni compositions, but it is somewhat less than the value of K 1 ¼ 1.3 MJ/m 3 obtained by Pauleve in neutron-irradiated bulk FeNi. 4 The Pauleve result suggests that the L1 0 composition to obtain optimal magnetic properties in bulk FeNi may lie closer to equiatomic FeNi with fewer Fe antisite defects.…”

“…5 and more recently by molecular beam epitaxy of FeNi films showing selected characteristics consistent with the tetragonal compound. [6][7][8][9][10] Laboratory synthesis of bulk L1 0 FeNi remains challenging because its low order-disorder temperature (T od ¼ 320 C) impedes conversion from the stable high temperature fcc phase by ordinary thermal processes.…”

Resonant x-ray diffraction revealing chemical disorder in sputtered L10FeNi on Si(0 0 1)

“…K eff is constant at about −1 MA/m which gives an increasing K U with M S since K shape is quadratically depending on M S . These values of K U are very small compared to previous reports of 0.8-0.9 MJ/m 3 [11,8]. Assuming a Slater-Pauling behaviour of M S the corresponding composition x Fe has been calculated, fig.…”

“…This means the tetragonal distortion should be compressive in-plane, which we do not observe in our samples. On the other hand we should be able to compare samples to Kojima [8] who obtained c/a not larger than 0.99. The out-of-plane correlation length in our samples is about 190Å to 240Å, so the samples are not fully coherent all the way through the film.…”

“…The FeNi L1 0 structure is a stable phase [9,10] but it is rare in nature, only occurring in meteorites, and it is difficult to synthesize due to the low temperature phase boundary. It has been studied in meteoritic samples [10,11,12] and has been synthesized through neutron bombardment (Néel [13] and Pauleve [14]), electron irradiation (Chamberod [15] and Reuter [16]), in thin film form (Kojima and Mizuguchi [8]), through severe plastic deformation (Lee [17]) and recently through a chemical process (Makino [18]). In all of these methods only very small amounts of the phase are produced.…”