From soft to hard magnetic Fe-Co-B by spontaneous strain: A combined first principle and thin film study

Abstract

In order to convert the well-known Fe-Co-B alloy from a soft to a hard magnet, we propose tetragonal strain by interstitial boron. Density functional theory reveals that when B atoms occupy octahedral interstitial sites, the bcc Fe-Co lattice is strained spontaneously. Such highly distorted Fe-Co is predicted to reach a strong magnetocrystalline anisotropy which may compete with shape anisotropy. Probing this theoretical suggestion experimentally, epitaxial films are examined. A spontaneous strain up to 5 % lattice distortion is obtained for B contents up to 4 at%, which leads to uniaxial anisotropy constants exceeding 0.5 MJ/m^3. However, a further addition of B results in a partial amorphization, which degrades both anisotropy and magnetization.

29 pages, 8 figures, 4 tables, supplementary PDF

References in corpus (4)

• Magnetic anisotropy energy of disordered tetragonal Fe-Co systems from ab initio alloy theory
• Degree of order dependence on magnetocrystalline anisotropy in bct FeCo alloys
• Increased magnetocrystalline anisotropy in epitaxial Fe-Co-C thin films with spontaneous strain
• Origin of the spin reorientation transitions in (Fe${}_{1-x}$Co${}_x$)${}_2$B alloys

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• Heteroepitaxial growth of tetragonal Mn${}_{2.7-x}$Fe${}_x$Ga${}_{1.3}$ (0 $⩽$ x $⩽$ 1.2) Heusler films with perpendicular magnetic anisotropy
• Structural and magnetic properties of Fe-Co-C alloys with tetragonal deformation: a first-principle study
• On the origin of perpendicular magnetic anisotropy in strained Fe-Co(-X) films
• Coulomb correlations and magnetic properties of L1${}_0$ FeCo: a DFT+DMFT study