Anomalous temperature dependence of training effect in specular spin valve using ultrathin Cr 2 O 3 -nano-oxide layer with magnetoelectric effect

Exchange bias from antiferromagnetic (AFM) oxides with a magnetoelectric (ME) effect has been studied for controlling ferromagnetic (FM) magnetizations by an applying electric field. However, thick ME oxides are needed for realizing the electrically controlled exchange biasing. Therefore, in this study the temperature dependencies of the training effect for the Cr 2 O 3 -nano-oxide-layer (NOL) are investigated for confirming the ME effect of the Cr 2 O 3 -NOL. The anomalous temperature tendencies of system dependent constant for exchange bias and magnetoresistance (MR), κ H ex and κ MR , were observed, which are probably originated from the ME effect of the Cr 2 O 3 -NOL because (1) these anomalous temperature tendencies could not be obtained in the CoO-NOL spin valve and (2) the κ H ex and κ MR are defined as the strength of the coupling between FM and AFM spins. It is remarkable result for us to confirm the possibility of the ME effect from the ultrathin Cr 2 O 3 layer (less than 1 nm) because the ME effect was observed in only thick ME materials.