Domain Structure and Wall Dynamics in High-PMA NiCo₂O₄ Thin Films

The inverse-spinel room-temperature ferrimagnetic NiCo₂O₄ (NCO) is of increasing interest, due to its demonstrated large perpendicular magnetic anisotropy, sensitivity of magnetic behavior to mixed cation valence, and deviations from ideal inverse spinel stoichiometry. Among the important information still missing about this material’s magnetic behavior from the literature includes information about the exchange interaction and domain structure of the magnetized film.

In this talk, we present data on temperature-dependent domain structure of thin film NiCo₂O₄ on MgAl₂O₄ (NCO/MAO) using XMCD-PEEM from the Advanced Light Source BL 11.0.1.1. The results show that magnetic domain sizes remain constant across a wide range of temperatures, which indicates strong pinning of the domains. Additionally, the resolution of XMCD-PEEM is sufficient to measure the domain wall widths, from which the micromagnetic exchange stiffness can be extracted. The exchange stiffness is up to an order of magnitude larger than similar materials with PMA, further solidifying NCO as an option in room-temperature magnetic applications.