Anisotropic Band-Split Magnetism in Magnetostrictive CoFe2O4

Single crystal spinel CoFe₂O₄ exhibits the largest room-temperature saturation magnetostriction among non-rare-earth compounds and a high Curie temperature (T₍c₎ ∼ 780 K), properties that are critical to a wide range of industrial and medical applications. Neutron spectroscopy reveals a large band splitting (∼60 meV) between two ferrimagnetic magnon branches, which is driven by site mixing between Co²⁺ and Fe³⁺ cations, and a significantly weaker magnetocrystalline anisotropy (∼3 meV). Central to this behavior is the competition between vast mismatched molecular fields on the tetrahedral A-site and octahedral B-site sublattices and the single-ion anisotropy on the B-site. This creates a strong, energetic anisotropy that locks the magnetic moment within each structural domain in place. As a result of these differing energy scales, switching structural domains is energetically favored over a global spin reorientation under applied magnetic fields, and this is what amplifies the magnetostrictive nature of CoFe₂O₄.