Anisotropic Band-Split Magnetism in Magnetostrictive CoFe2 O4

Single crystal spinel CoFe2 O4 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 Co 2+ 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 CoFe2 O4 .