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The Topological Hall Effect (THE) has been considered a hallmark of magnetic skyrmions in SrRuO3 single films and heterostructures. Alternative interpretations suggest that the THE-like anomalies could also originate from multi-channel anomalous Hall effects (AHEs) induced by structural inhomogeneity. Here, we reveal another type of THE-like anomaly in SrRuO3 films that was rarely reported previously. By scanning minor loops of the Hall resistivity of ultrathin SrRuO3 films, we demonstrate that the increased saturation resistivity and reversed polarity with decreasing a scanning field cannot be explained by THE, while it shows consistence with spatially inhomogeneous AHE. Our research provides a simple but effective way to quantitatively distinguish between THE and inhomogeneous AHE in those magnetic systems even beyond SrRuO3.

The reversible topotactic phase transformation between brownmillerite SrCoO2.5 to perovskite SrCoO3 has attracted more and more attention for potential applications as solid oxide fuels and electrolysis cells. However, the relatively easy transformation result from small thermal stable energy barriers between the two phases leads to unstable the structures. In the paper, amounts of SrCoO3-δ films have been prepared by pulsed laser deposition at optimized growth conditions with the temperature range of 590-720°C. The X-ray diffraction (XRD) results demonstrated that a phase competition emerged around 650°C. The Gibbs free energies of two phases at high temperature revealed the difference of stability of these two phases under different growth temperature. The optical spectroscopies and X-ray photoelectron spectroscopies were used to verify the electronic structure and chemical state differences between the two phases with distinct crystal structures.

We studied using organic liquids (cyclohexane, n-butanol, and ethylene glycol) to modulate the transport properties at room temperature of an epitaxial VO2 film on a VO2/Al2O3 heterostructure. The resistance of the VO2 film increased when coated with cyclohexane or n-butanol, with maximum changes of 31% and 3.8%, respectively. In contrast, it decreased when coated with ethylene glycol, with a maximum change of −7.7%. In all cases, the resistance recovered to its original value after removing the organic liquid. This organic-liquid-induced reversible resistance switching suggests that VO2 films can be used as organic molecular sensors.

Large scale electronic phase separation (EPS) between ferromagnetic metallic and charge-ordered insulating phases in La5/8-yPryCa3/8MnO3 (y = 0.3) (LPCMO) is very sensitive to the structural changes. This work investigates the effects of post-annealing on the strain states and electrical transport properties of LPCMO films epitaxially grown on (001)pc SrTiO3 (tensile strain), LaAlO3 (compressive strain) and NdGaO3 (near-zero strain) substrates. Before annealing, all the films are coherent-epitaxial and insulating through the measured temperature range. Obvious change of film lattice is observed during the post-annealing: the in-plane strain in LPCMO/LAO varies from −1.5% to −0.1% while that in LPCMO/STO changes from 1.6% to 1.3%, and the lattice of LPCMO/NGO keeps constant because of the good lattice-match between LPCMO and NGO. Consequently, the varied film strain leads to the emergence of metal-insulator transitions (MIT) and shift of the critical transition temperature in the electrical transport. These results demonstrate that lattice-mismatch combined with post-annealing is an effective approach to tune strain in epitaxial LPCMO films, and thus to control the EPS and MIT in the films.

The metal-insulator transition (MIT) in strong correlated electron materials can be induced by external perturbation in forms of thermal, electrical, optical, or magnetic fields. We report on the DC current induced MIT in epitaxial Sm0.6Nd0.4NiO3 (SNNO) thin film deposited by pulsed laser deposition on (001)-LaAlO3 substrate. It was found that the MIT in SNNO film not only can be triggered by thermal, but also can be induced by DC current. The TMI of SNNO film decreases from 282 K to 200 K with the DC current density increasing from 0.003 × 109 A•m−2 to 4.9 × 109 A•m−2. Based on the resistivity curves measured at different temperatures, the MIT phase diagram has been successfully constructed.