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.