Conversion of FeCo from soft to hard magnetic material by lattice engineering and nanopatterning

The development of magnetic materials with large uniaxial magnetic anisotropy (Ku) and high saturation magnetization has attracted much attention in various areas such as high-density magnetic storage, spintronic devices, and permanent magnets. Although FeCo alloys with the body-centred cubic structure exhibit the highest Ms among all transition metal alloys, their low Ku and coercivity (Hc) make them unsuitable for these applications. However, recent first-principles calculations have predicted large Ku for the FeCo films with the body-centred tetragonal structure. In this work, we experimentally investigated the hard magnetic properties and magnetic domain structures of nanopatterned FeCo alloy thin films. As a result, a relatively large value of the perpendicular uniaxial magnetic anisotropy Ku = 2.1 × 106 J·m−3 was obtained, while the Hc of the nanopatterned FeCo layers increased with decreasing dot pattern size. The maximum Hc measured in this study was 4.8 × 105 A·m−1, and the corresponding value of μ0Hc was 0.60 T, where μ0 represented the vacuum permeability.