Magnetic Anisotropy in Iron-Cobalt Alloys

Iron-cobalt alloys represent a class of rare-earth-free magnetic materials that combine high saturation magnetisation with tunable magnetic anisotropy. Magnetic anisotropy describes the directional dependence of a material’s magnetic properties, which is crucial for the performance of permanent magnets, spintronic devices and data storage media. In Fe–Co systems, a body-centred cubic structure exhibits exceptional magnetisation but lacks sufficient uniaxial anisotropy for many applications. By inducing a tetragonal distortion or through compositional engineering, researchers have achieved enhanced anisotropy energy, improved coercivity and controlled easy axes of magnetisation. Recent advances include lattice engineering via elemental additions, epitaxial stress in thin films and nanopatterning approaches that collectively aim to stabilise a body-centred tetragonal phase, boost anisotropy constants and enable rare-earth-free magnets with high energy products. These developments have broad implications for sustainable energy technologies and next-generation electronic devices.

Research from Nature Portfolio

Recent investigations have demonstrated that the addition of vanadium and nitrogen to Fe–Co systems stabilises a body-centred tetragonal lattice, yielding uniaxial anisotropy energies above 1 × 10^6 J m^−3 in both thin films and bulk foils. Nanopatterning of epitaxial FeCo layers has further converted a soft magnetic alloy into a hard magnet by creating nanoscale patterned dots, which exhibit perpendicular anisotropy and coercivities approaching 0.6 T. In bulk forms, rolled and ammonia-gas-nitrided Fe–Co–V ingots maintain a tetragonal distortion (c/a≈1.1) at micrometre thicknesses, resulting in large uniaxial anisotropy without rare-earth elements. These studies collectively highlight the feasibility of combining lattice distortion and compositional tuning to achieve high-performance, rare-earth-free magnetic materials.

Magnetic Anisotropy in Iron-Cobalt Alloys publication trend

The graph below shows the total number of articles in magnetic anisotropy in iron-cobalt alloys across all publications each year (not limited to Nature Index journals).

Technical terms

Magnetic anisotropy: The dependence of a material’s magnetic energy on the orientation of its magnetisation relative to its crystal axes.

Uniaxial anisotropy: A form of magnetic anisotropy where there is one preferred easy axis of magnetisation.

Body-centred tetragonal (bct) structure: A crystal lattice distorted from cubic symmetry by differing axial ratios, enhancing anisotropy.

Coercivity: The magnetic field strength required to reduce the magnetisation of a material to zero.

Saturation magnetisation: The maximum magnetisation achieved when all magnetic moments are aligned.

Magnetocrystalline anisotropy: The component of magnetic anisotropy originating from spin–orbit coupling within the crystal lattice.

Stoner–Wohlfarth model: A theoretical framework describing the magnetisation reversal of single-domain particles under applied fields.

References

1. Investigation of the body-centred tetragonal structure of Fe–Co–V–N Bulk foils using the rolling and ammonia-gas-nitriding method. Scientific Reports (2023).
2. Conversion of FeCo from soft to hard magnetic material by lattice engineering and nanopatterning. Scientific Reports (2017).
3. Stabilisation of tetragonal FeCo structure with high magnetic anisotropy by the addition of V and N elements. Scientific Reports (2019).
4. Strain-induced control of magnetocrystalline anisotropy energy in FeCo thin films. Journal of Magnetism and Magnetic Materials (2021).
5. TEM observation of nitrogen-tunable bcc–bct–fcc transformation of iron-cobalt with added vanadium. AIP Advances (2020).
6. Determination of anisotropy constants via fitting of magnetic hysteresis to numerical calculation of Stoner–Wohlfarth model. AIP Advances (2021).