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

The development of magnetic materials with large uniaxial magnetic anisotropy (K _u) 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 M _s among all transition metal alloys, their low K _u and coercivity (H _c) make them unsuitable for these applications. However, recent first-principles calculations have predicted large K _u 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 K _u = 2.1 × 10⁶ J·m^-3 was obtained, while the H _c of the nanopatterned FeCo layers increased with decreasing dot pattern size. The maximum H _c measured in this study was 4.8 × 10⁵ A·m^-1, and the corresponding value of μ ₀ H _c was 0.60 T, where μ ₀ represented the vacuum permeability.