Topological spin textures as an emerging class of topological matter offer a medium for information storage and processing. The recently discovered topological Hall effect (THE) is considered as a fingerprint for electrically probing the Dzyaloshinskii–Moriya (DM) interaction and corresponding non-trivial spin-textures. In this paper, the THE and its electrical control are observed in ultrathin (⩽8 unit cells. u.c.) 4D ferromagnetic SrRuO ₃ films grown on SrTiO ₃ (0 0 1) substrates, indicating the existence of gate-bias-tunable DM interaction in the single SrRuO ₃ layer without contacting 5D oxide SrIrO ₃ layer. High-resolution lattice structure analysis revealed that the interfacial RuO ₆ octahedral tilting induced by local orthorhombic-to-tetragonal structural phase transition exists across the SrRuO ₃ /SrTiO ₃ interface, which naturally breaks the inversion symmetry. Our theoretical calculations demonstrate that the DM interaction arises owing to the broken inversion symmetry and strong spin–orbit interaction of 4D SrRuO ₃ . This interfacial RuO ₆ octahedral tilting-induced DM interaction can stabilize the Néel-type magnetic skyrmions, which in turn accounts for the observed THE in transport. Besides the fundamental significance, the understanding of THE in oxides and its electrical manipulation presented in this work could advance the low power cost topological electronic and spintronic applications.

By investigating the nature of the first-order magnetostructural phase transition, we point out the origin of large overestimation of magnetic entropy changes calculated by directly applying the Maxwell relation. Furthermore, if the mass variations in ferromagnetic and paramagnetic phases on temperature are taken into consideration in two-phase region, taking ${\text{MnAsC}}_{\text{x}}$ , (Mn, Al)As, and ${\text{Mn}}_{0.994}{\text{Fe}}_{0.004}\text{As}$ compounds as example, based on the modified Maxwell relation, the large overestimation and discrepancy of magnetic entropy changes disappear. The magnetic entropy changes are equivalent with the values by Clausius–Claperyon equation, indicating the validity of this modified approach.

SrRuO₃ (SRO)-based heterostructures have attracted much attention for potential applications such as electrodes, oxide spintronics, topological electronics and electrocatalytic function mainly due to the strong spin–orbit coupling, itinerant ferromagnetism with 4d electrons, high metallic conductivity, perpendicular magnetic anisotropy and rich oxygen octahedral distortion of SRO. Here, this work aims to offer a timely and systematic review on SRO-based heterostructures for its emerging opportunities in oxide spintronic and topological electronic applications. We first present a brief summary of the current status in SRO-based heterostructures and describe the motivations of this review. We then briefly review the surface and interface modulation in SRO-based heterostructures, including oxygen octahedral distortions (antiferrodistortive mode and ferroelectric mode) engineering and ion defect engineering. In the third part, we discuss the spin-charge interconversion phenomena in SRO-based heterostructures, covering the inverse spin Hall effect and current-induced spin-orbit torques. Particularly, in the fourth part, we discuss the emergent topological Hall effect and underlying mechanism in SRO-based heterostructures, including the two-channel anomalous Hall effect and Berry phase manipulation. The fifth part presents the magnetic Weyl fermions and its electric-field control of SRO films. We finally conclude with a discussion of challenges and prospects of SRO-based heterostructures, which provides a guidance for exploring novel physical properties and designing multifunctional devices based on SRO.

Voltage control of magnetism has been considered and proven to be an efficient actuation protocol to boost energy efficiency in a widespread range of spintronic devices. In particular, the study of voltage-induced changes in magnetism by the magneto-ionic effect has rapidly accelerated during the past few years due to the versatile advantages of effective control, non-volatile nature, low-power cost, etc. In this perspective, we briefly outline the recent research progress on the voltage-controlled magneto-ionic effect by using two representative dielectric gating materials [ionic liquids (ILs) and ionic conductors] in different functional solid-state heterostructures and devices, mainly including both the ferroic-order [ferromagnetic, ferroelectric (FE), and multiferroic] oxides and magnetic metal-based heterostructure systems. Within the framework of ferroic oxide heterostructures, we have also extended the IL control to FE materials, clarifying that FE properties can also be tailored by electrostatic and electrochemical methods. Finally, we discuss the challenges and future aspects of magneto-ionics, which would inspire more in-depth studies and promote the practical applications.

The magnetic properties of 10 nm size $\text{Ni}{\left(\text{OH}\right)}_2$ nanoparticles prepared by sol-gel method have been studied. The magnetic moments increase with decreasing temperature in a low applied field, which is due to the spin-frozen-like state at low temperatures, and the metamagnetic transition is not clearly observed even in an applied field of 70 kOe due to the size effect. Furthermore, the transition from paramagnetic to antiferromagnetic in the $\text{Ni}{\left(\text{OH}\right)}_2$ nanoparticles occurs at lower temperature (22 K).