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 x 10(6) 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 x 10(5) A.m(-1), and the corresponding value of mu H-0(c) was 0.60 T, where mu(0) represented the vacuum permeability.