Quantum Oscillations in Half Metallic Ferromagnetic CrO₂ Epitaxial Films

We investigate the low-temperature, high-field magnetotransport behavior of epitaxially grown CrO₂ thin films. CrO₂ is a half metal oxide with near perfect spin polarization of 96-98% and a ferromagnetic (FM) ordering temperature of T_c ~ 390 K. Its double-exchange FM ordering and relatively large saturation magnetization makes it attractive for spintronic applications. We report on the magnetization and electron transport measurements which confirm high quality samples varying in thickness from less than 5 nm to bulk. Deviation from Bloch’s law in the thinnest films suggests a transition to a 2D state with robust FM nature. In the limit of high fields (12 T) and low temperatures (1.8 K) we observe strong crystalline axis-dependent quantum oscillations in the longitudinal magnetoresistance (ρ_xx). The nontrivial thickness-dependent out-of-plane ρ_xx exhibits a maximum value of 6.58%. Our results address gaps in experimental research on the quantum electronic and magnetotransport properties of CrO₂ films. We highlight CrO₂ as an exotic half-metallic system with unique and enhanced properties that promote fundamental studies of other novel half-metallic materials. This work was supported by the National Science Foundation under Grant No. DMR-2202514 and a Seed Grant from Brown University.