Modulating Exchange Bias, Anisotropic Magnetoresistance, and Planar Hall Resistance of Flexible Co/MnN Epitaxial Bilayers on Mica by Bending Strain

The integration of ferromagnetic/antiferromagnetic bilayers with exchange bias effect on flexible substrates is crucial for flexible spintronics. Here, the epitaxial Co/MnN bilayers are deposited on mica by facing-target sputtering. A large in-plane exchange bias field (H_EB) of 1800 Oe with a coercive field (H_C) of 2750 Oe appears in the Co (3.8 nm)/MnN (15.0 nm) bilayer at 5 K after field cooling from 300 to 5 K. Effective interfacial exchange energy J_eff of the Co/MnN bilayer is 0.83 erg/cm². The strain-induced maximum increase of H_EB and H_C reaches 18% and 21%, respectively, in the Co(3.8 nm)/MnN(15.0 nm) bilayer. Strain-modulated H_EB is attributed to the change of interfacial exchange coupling between Co and MnN layers. H_EB is inversely proportional to Co thickness but independent of MnN thickness. The change of H_EB is less than 5% after 100 bending cycles, indicating mechanical durability. The out-of-plane exchange bias also appears since Co spins are not fully reversed due to the strong pinning effect. Anisotropic magnetoresistance (AMR) and planar Hall resistance (R_xy) show obvious hysteresis due to H_EB. Exchange bias-induced phase difference of AMR and R_xy almost remains unchanged at different bending strains. The results provide the basis for understanding the bending strain tailored exchange bias.