The high magnetoresistance performance of epitaxial half-metallic CrO₂-based magnetic junctions

Half-metallic chromium dioxide (CrO₂) is an ideal spintronic material due to its near-full spin polarization and ultralow Gilbert damping at room temperature. Based on theoretical calculations, we found that the tunneling magnetoresistance (TMR) ratios of the CrO₂/XO₂/CrO₂ (X= Ti and Sn) magnetic tunnel junctions (MTJs) can reach up to the order of magnitude of 10⁵%, and the magnetoresistance (MR) ratio of CrO₂/RuO₂/CrO₂ magnetic junctions (MJs) can reach the order of magnitude of 10⁴%. In addition, we succeeded in fabricating epitaxial CrO₂-based MTJs (CrO₂/TiO₂/CrO₂ and CrO₂/TiO₂/Co₂FeAl) with TiO₂ tunnel barriers of varying thickness. Evident TMR effects were observed for all CrO₂-based MTJs with the highest MR ratio of 8.55% for the CrO₂/TiO₂/Co₂FeAl MTJ at 10 K. The MR ratios of CrO₂-based MTJs in our studies were lower than theoretical expectations, which could be due to the possible mixture of interface atoms and Cr magnetization reversal. Moreover, the existence of oxygen vacancies in the TiO₂ tunnel barrier also weakened the TMR effect significantly due to increased spin scattering, and the annealing treatment in an oxygen atmosphere led to an increase in the MR ratio of the CrO₂/TiO₂/Co₂FeAl MTJ by about 33% in comparison with the unannealed MTJ, which is consistent with theoretical calculations.