Electric-Field Reversible Switching of the Exchange Spring and Exchange Bias Effect in SrCoO_3–x/La_0.7Sr_0.3MnO₃ Heterostructures

The technique of electrical field to manipulate physicochemical properties of oxide heterostructures has ample potential in electronic and ionitronic devices. SrCoO3–x is a famous “sponge” material displaying topotactic structural phase transition from perovskite (0 ≤ x ≤ 0.25) to brownmillerite (x = 0.5) accompanied by the magnetic phase transition from ferromagnetism to antiferromagnetism, which can be controlled reversibly by electric field via the ionic liquid gating method. Here, the exchange spring effect can be observed at the perovskite SrCoO3–x (P-SCO)/La0.7Sr0.3MnO3 (LSMO) bilayer, while the exchange bias effect is received at the brownmillerite SrCoO2.5 (B-SCO)/LSMO bilayer. The reversible and nonvolatile switching of the exchange spring and exchange bias effect can be achieved in these SCO3–x/LSMO bilayers by utilizing ionic liquid gating to control the annihilation or generation of oxygen vacancies. In addition, the variations in the stacking orders of these SCO3–x/LSMO bilayers are investigated because the previous SCO3–x layer always acts as the cover layer. It is worth noting that LSMO/SCO3–x bilayer magnetization is strongly suppressed when the SCO3–x layer is used as the bottom layer. Combined with the X-ray line dichroism measurements, it is suggested that the bottom SCO3–x layer would induce the spin arrangements in the LSMO layer to have the tendency toward the out-of-plane orientation. This is the reason for the sharp decrease in magnetization of LSMO/SCO3–x bilayers. Our investigations accomplish a reversible control of the exchange coupling transition in all-oxide bilayers and provide the foundation for further electric-field control of magnetic properties.