Voltage-driven strain-mediated modulation of exchange bias in Ir₂₀Mn₈₀/Fe₈₀Ga₂₀/Ta/⟨011⟩-oriented PMN-32PT heterostructures

Manipulation of exchange bias with electric field is appealing to boost energy efficiency in spintronic devices. Here, this effect is shown at room temperature in Ir₂₀Mn₈₀/Fe₈₀Ga₂₀/Ta layers grown onto ⟨011⟩-oriented PMN-32PT single crystals. After magnetic field-cooling (FC) along the [01-1] and [100] in-plane directions of PMN-32PT and upon allowing the system to relax through consecutive hysteresis loops (training effect), the exchange bias field (H_EB) is measured under the action of voltage (out-of-plane poling). Depending on the applied voltage (magnitude and sign), H_EB can either increase or decrease with respect to its value at 0 V. The relative variations of H_EB are 24% and 5.5% after FC along the [01-1] and [100] directions, respectively. These results stem from strain-mediated magnetoelectric coupling. The applied electric field causes changes in the coercivity and the squareness ratio of the films, suggesting a reorientation of the effective magnetic easy axis in Fe₈₀Ga₂₀. However, larger H_EB values are observed when the squareness ratio is lower. It is claimed that the effect of voltage is equivalent to an in-plane component of an applied magnetic field oriented perpendicular to the cooling field direction. Perpendicular in-plane magnetic fields have been shown to induce an increase in exchange bias in some ferromagnetic/antiferromagnetic systems due to partial recovery of the untrained antiferromagnetic state. Remarkably, here, this effect is directly induced with voltage, therefore enhancing energy efficiency.