RESUMEN
Effective manipulation of magnetic properties in transition-metal oxides is one of the crucial issues for the application of materials. Up to now, most investigations have focused on electrolyte-based ionic control, which is limited by the slow speed. In this work, the interfacial coupling of the SrCoO2.5/La0.7Ca0.3MnO3 (LCMO) bilayer is effectively modulated with fast response time. After being treated with diluted acetic acid, the bilayer changes from antiferromagnetic/ferromagnetic (AFM/FM) coupling to FM/FM coupling and the Curie temperature is also effectively increased. Meanwhile, the corresponding electric transport properties are modulated within a very short time. Combined with the structure characterization and X-ray absorption measurements, we find that the top SrCoO2.5 layer is changed from the antiferromagnetic insulator to the ferromagnetic metal phase, which is attributed to the formation of the active oxygen species due to the reaction between the protons in the acid and the SrCoO2.5 layer. The bottom LCMO layer remains unchanged during this process. The response time of the bilayer with the acid treatment method is more than an order of magnitude faster than other methods. It is expected that this acid treatment method may open more possibilities for manipulating the magnetic and electric properties in oxide-based devices.
RESUMEN
The interface of perovskite heterostructures has been shown to exhibit various electronic and magnetic phases such as two-dimensional electron gas, magnetism, superconductivity, and electronic phase separation. These rich phases are expected due to the strong interplay between spin, charge, and orbital degree of freedom at the interface. In this work, the polar and nonpolar interfaces are designed in LaMnO3-based (LMO) superlattices to investigate the difference in magnetic and transport properties. For the polar interface in a LMO/SrMnO3 superlattice, a novel robust ferromagnetism, exchange bias effect, vertical magnetization shift, and metallic behaviors coexist due to the polar catastrophe, which results in a double exchange coupling effect in the interface. For the nonpolar interface in a LMO/LaNiO3 superlattice, only the ferromagnetism and exchange bias effect characteristics exist due to the polar continuous interface. This is attributed to the charge transfer between Mn3+ and Ni3+ ions at the interface. Therefore, transition metal oxides exhibit various novel physical properties due to the strong correlation of d electrons and the polar and nonpolar interfaces. Our observations may provide an approach to further tune the properties using the selected polar and nonpolar oxide interfaces.
RESUMEN
The dimensionality of the crystal structure plays a vital role in artificial heterostructures composed of different transition metal oxides. Nonlinear layer-thickness dependence of the exchange bias effect was observed in high-quality SrCuO2/La0.7Sr0.3MnO (LSMO) superlattices induced in the present work by dimensional evolution. In the SCO(n)/LSMO(8) superlattices with thickness below the critical value (5 u.c.), the exchange bias effect decreased and the saturated magnetization increased with increase in SCO thickness. By contrast, the exchange bias effect increased and the saturated magnetization decreased in S(n)L(8) superlattices with thickness above the critical value. This is because the lattice SCO material underwent a breathing-like structural transformation from the planar to a chain-like structure. The results indicate the interfacial superexchange coupling mainly present in the chain-like S(n)L(8) superlattices through X-ray absorption spectroscopy and first principles calculations. This superexchange coupling generated a weak localized magnetic moment to pin the adjacent ferromagnetic layer. However, in the thicker S(n)L(8) superlattices, evolution of magnetic properties was induced by the long-range antiferromagnetic order in the planar SCO layer. Our findings demonstrate that the dimensionality driven structural variation is an effective method to manipulate the electronic reconstruction and the associated physical properties, paving a pathway for the advancement of strongly correlated materials.
RESUMEN
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.
