Work

Direct observation of thermal spin depolarization in a type I B half-metal Ni Co 2 O 4 by spin-resolved photoemission

Year: 2026

Type: article

Abstract: Half-metals (HMs), characterized by 100% spin polarization at the Fermi level ( E F ), are ideal candidates for future spintronic memory devices. However, their spin polarization rapidly decreases with temperature, limiting their practical implementation. While this degradation has been theoretically attributed to nonquasiparticle (NQP) states—many-body electronic states arising from electron-magnon interactions that reduce spin polarization near E F —experimental verification remains limited. Here, we report the temperature evolution of the electronic states in epitaxial Ni Co 2 O 4 (NCO) thin films, a predicted type I B HM where the main spectral weight of NQP states lies below E F . Using high-resolution bulk-sensitive laser-based spin-resolved photoemission spectroscopy, we reveal that at 20 K, a metallic Fermi edge is observed in the minority-spin states but is absent in the majority-spin states, providing spectroscopic evidence for the half-metallicity of NCO. As temperature increases, majority-spin spectral weight emerges at E F , and spin polarization near E F decreases—consistent with the emergence of NQP states. The onset of this behavior occurs around 100 K. Our results suggest that NCO provides a promising platform for investigating NQP-related many-body effects in type I B HMs, guiding the design of spintronic materials with robust high-temperature spin polarization.

Source: Physical Review Research

DOI: 10.1103/9hsj-vmwn