Abstract
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.
Highlights
The continuously increasing power consumption in motors[1] and data storage devices[2,3] containing permanent magnets has become a serious issue
Where μ0 is the vacuum permeability. This expression is based on the single domain theory that assumes hard magnetic properties of a material with a sufficiently high value of Hc4
In order to prevent the generation of thermal fluctuations and, bit errors, the thermal stability factor KuV of a magnetic layer must be much higher than the thermal energy kBT
Summary
The tetragonally distorted FeCo(Al) thin film with a lattice parameter ratio c/a of 1.01–1.21 and high Ku of 2.1 × 106 J·m−3 was fabricated. A coercivity of 0.60 T was obtained for the nanopatterned FeCo layer with a thickness of 20.0 nm and dot pattern diameter of 50 nm. These results demonstrate that the combination of lattice engineering (introduction of tetragonal distortion into the structure of FeCo alloys) and nanopatterning (fabrication of patterns smaller than the single domain size) yields materials possessing high values of Ku, Hc, and Ms the produced materials exhibit high potentials for future applications requiring high magnetic anisotropy and flux density, such as high-performance permanent magnets for motors and data storage devices
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