Direct Observation of Room-Temperature Stable Magnetism in LaAlO₃/SrTiO₃ Heterostructures

Along with an unexpected conducting interface between nonmagnetic insulating perovskites LaAlO₃ and SrTiO₃ (LaAlO₃/SrTiO₃), striking interfacial magnetisms have been observed in LaAlO₃/SrTiO₃ heterostructures. Interestingly, the strength of the interfacial magnetic moment is found to be dependent on oxygen partial pressures during the growth process. This raises an important, fundamental question on the origin of these remarkable interfacial magnetic orderings. Here, we report a direct evidence of room-temperature stable magnetism in a LaAlO₃/SrTiO₃ heterostructure prepared at high oxygen partial pressure by using element-specific soft X-ray magnetic circular dichroism at both Ti L_3,2 and O K edges. By combining X-ray absorption spectroscopy at both Ti L_3,2 and O K edges and first-principles calculations, we qualitatively ascribe that this strong magnetic ordering with dominant interfacial Ti³⁺ character is due to the coexistence of LaAlO₃ surface oxygen vacancies and interfacial (Ti_Al–Al_Ti) antisite defects. On the basis of this new understanding, we revisit the origin of the weak magnetism in LaAlO₃/SrTiO₃ heterostructures prepared at low oxygen partial pressures. Our calculations show that LaAlO₃ surface oxygen vacancies are responsible for the weak magnetism at the interface. Our result provides direct evidence on the presence of room-temperature stable magnetism and a novel perspective to understand magnetic and electronic reconstructions at such strategic oxide interfaces

The Mechanism of Electrolyte Gating on High‑<i>T</i>_<i>c</i> Cuprates: The Role of Oxygen Migration and Electrostatics

Electrolyte gating is widely used to induce large carrier density modulation on solid surfaces to explore various properties. Most of past works have attributed the charge modulation to electrostatic field effect. However, some recent reports have argued that the electrolyte gating effect in VO₂, TiO₂, and SrTiO₃ originated from field-induced oxygen vacancy formation. This gives rise to a controversy about the gating mechanism, and it is therefore vital to reveal the relationship between the role of electrolyte gating and the intrinsic properties of materials. Here, we report entirely different mechanisms of electrolyte gating on two high-<i>T</i>_<i>c</i> cuprates, NdBa₂Cu₃O_7−δ (NBCO) and Pr_2–<i>x</i>Ce_<i>x</i>CuO₄ (PCCO), with different crystal structures. We show that field-induced oxygen vacancy formation in CuO chains of NBCO plays the dominant role, while it is mainly an electrostatic field effect in the case of PCCO. The possible reason is that NBCO has mobile oxygen in CuO chains, while PCCO does not. Our study helps clarify the controversy relating to the mechanism of electrolyte gating, leading to a better understanding of the role of oxygen electro migration which is very material specific