Topological Hall Effect In Proton-doped SrRuO₃ Films

The intense competition among various energies can stabilize the topological spin textures.Among them,magnetic skyrmions have attracted extensive attention of scientists due to their rich and novel topological properties and potential applications.SrRuO₃(SRO),as the only material in 4d transition metal oxides with coexistence of itinerant ferromagnetism and spin-orbit coupling,has become a popular material for the study of magnetic skyrmions and the Topological Hall effect(THE).However,recently,most of the researches on THE in SRO are based on the SRO heterojunction or few-unit-cell-thick ultrathin films.The fabrication difficulty of high quality heterostructure and ultrathin film brings great challenges for future practical applications.In this paper,the hydrogen ions(proton)are successfully doped in the a single-layer SRO film(>10nm)by means of catalytic assisted hydrogenation,which causes small change in lattice constant of the SRO film,and significantly adjusts the magnetic and electrical properties.The insertion of protons can induce large ionic displacement and strong Dzyaloshinskii-Moriya(DM)interaction,which favors the emergence of the associated THE.The main contents and results are as follows:1.A series of high-quality SRO films with different thicknesses were deposited on(001)-oriented SrTiO₃(STO)substrates by pulsed laser deposition.Through the characterization of the surface morphology and crystal structure of the films,it was found that the prepared SRO films had atomically flat surface morphology and good crystallinity.The tests of the electrical transport properties of SRO films with different thicknesses show that the SRO films have good metallicity,and the metallicity decreases as the film thickness decreases.The Curie temperature(T_C)at which the SRO film transitions from the ferromagnetic state to the paramagnetic state will also decrease as the thickness of the SRO film decreases.In addition,we also study the anomalous Hall effect(AHE)in SRO.Different from traditional ferromagnetic materials,the AHE in SRO exhibits a non-monotonic change with temperature below T_C,and there will be a sign transition at a certain temperature,and the transition temperature will also increase with increasing film thickness.2.Based on the growth of high-quality SRO films,the SRO films were successfully doped with protons by annealing the SRO films in a hydrogen atmosphere using Pt electrode as a catalyst,and the reversible regulation of the structural changes of SRO was achieved.Without introducing large structural deformation,a large carrier modulation of the SRO is achieved,and the electrical and magnetic properties are significantly tuned.With the continuous increase of the hydrogenation degree,the resistance of the SRO film increases,the metallicity weakens,and the ferromagnetism is gradually suppressed.These results suggest that this catalytically assisted hydrogenation provides a novel approach to tuning the physical properties of SRO thin films.3.High-resolution transmission electron microscopy results indicate that based on the method of catalytic-assisted hydrogenation,the doped protons do not cause large lattice expansion in SRO lattice,but it leads to a vertical ionic displacement?_Ru-Obetween Ru and O in the Ru O₂ plane.Theoretical calculation also demonstrates that the proton doping(below 1/unit cell)in the SRO lattice will cause increase in?_Ru-O and significant enhancement of DM interaction due to lattice distortion of oxygen octahedra breaking the spatial inversion symmetry.The transport measurement results show that there is significant THE in a large temperature range.Below 30 K,two kinds of THE with opposite signs appear.These experimental results provide a new strategy to study the topological spin structure and induce the production of THE in the SRO system.