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arXiv · 2512.15683

Anisotropic Band-Split Magnetism in Magnetostrictive CoFe$_2$O$_4$

Harry Lane·Guratinder Kaur·Masahiro Kawamata·Yusuke Nambu·Lukas Keller·Russell A. Ewings·David J. Voneshen·Travis J. Williams·Helen C. Walker·Dwight Viehland·Peter M. Gehring·Chris Stock
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Abstract

Single crystal spinel CoFe$_2$O$_4$ exhibits the largest room-temperature saturation magnetostriction among non-rare-earth compounds and a high Curie temperature ($T_c \sim 780$ K), properties that are critical to a wide range of industrial and medical applications. Neutron spectroscopy reveals a large band splitting ($\sim$ 60 meV) between two ferrimagnetic magnon branches, which is driven by site mixing between Co$^{2+}$ and Fe$^{3+}$ cations, and a significantly weaker magnetocrystalline anisotropy ($\sim$ 3 meV). Central to this behavior is the competition between extremely large 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 CoFe$_2$O$_4$.

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Harry Lane, Guratinder Kaur, Masahiro Kawamata, Yusuke Nambu, Lukas Keller, Russell A. Ewings, David J. Voneshen, Travis J. Williams, Helen C. Walker, Dwight Viehland, Peter M. Gehring, Chris Stock. 2025-12-17. Anisotropic Band-Split Magnetism in Magnetostrictive CoFe$_2$O$_4$. https://doi.org/10.1002/adfm.202516830

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