We investigate magnetoelectric switching of perpendicular exchange bias with very low coercivity in a Pt/Co/Ir/Cr2O3/Pt epitaxial film. We also optimize the suitable Ir spacer thickness so that the film exhibits the perpendicular exchange bias greater than the coercivity up to the vicinity of the Néel temperature. Main impact of the Ir spacer layer is the significant reduction of coercivity less than 0.5 mT in maintaining both the perpendicular magnetic anisotropy and the perpendicular exchange bias. For the suitable structure, the perpendicular exchange bias was isothermally switched by the gate voltage in combination with the magnetic field. Analysis of the hysteresis of the exchange bias field as a function of the gate voltage suggested that the magnetoelectric coefficient was comparable to the reported value. This implies that the Ir layer does not degrade the efficiency to transfer the magnetoelectrically controlled antiferromagnetic order parameter to the ferromagnetic Pt/Co/Ir trilayer.

We investigate the magneto-optic Kerr effect in perpendicularly magnetized Pt/Co/Ir/Cr2O3/Pt thin films, associated with the antiferromagnetic–paramagnetic transition of the Cr2O3 layer. The magneto-optic Kerr rotation angle (θ K) shows oscillatory behavior as a function of the photon energy of incident light owing to interference in the Cr2O3 layer. The temperature dependence of θ K at 2.67 eV (λ = 465 nm), at which the largest θ K is obtained, shows a sharp dip at 287.0 K. This is similar to the reported Néel temperature for Cr2O3 thin films. Although the θ K spectra measured at several temperatures are generally explained by the classical interference model, θ K is enhanced at 2.36–2.79 eV (λ = 525–445 nm) close to the dip temperature. This peculiar enhancement in θ K is discussed on the basis of the anomaly in the optical parameters of the Cr2O3 layer associated with the antiferromagnetic–paramagnetic transition.