Electronic Inhomogeneity Influence on the Anomalous Hall Resistivity Loops of SrRuO₃ Epitaxially Interfaced with 5d Perovskites

Abstract

SrRuO 3 , a 4d ferromagnet with multiple Weyl nodes at the Fermi level, offers a rich playground to design epitaxial heterostructures and superlattices with fascinating magnetic and magnetotransport properties. Interfacing ultrathin SrRuO 3 layers with large spin−orbit coupling 5d transition-metal oxides, such as SrIrO 3 , results in pronounced peaklike anomalies in the magnetic field dependence of the Hall resistivity. Such anomalies have been attributed either to the formation of Neél-type skyrmions or to modifications of the Berry curvature of the topologically nontrivial conduction bands near the Fermi level of SrRuO 3 . Here, epitaxial multilayers based on SrRuO 3 interfaced with 5d perovskite oxides, such as SrIrO 3 and SrHfO 3 , were studied. This work focuses on the magnetotransport properties of the multilayers, aiming to unravel the role played by the interfaces with 5d perovskites in the peaklike anomalies of the Hall resistance loops of SrRuO 3 layers. Interfacing with large band gap insulating SrHfO 3 layers did not influence the anomalous Hall resistance loops, while interfacing with the nominally paramagnetic semimetal SrIrO 3 resulted in pronounced peaklike anomalies, which have been lately attributed to a topological Hall effect contribution as a result of skyrmions. This interpretation is, however, under strong debate and lately alternative causes, such as inhomogeneity of the thickness and the electronic properties of the SrRuO 3 layers, have been considered. Aligned with these latter proposals, our findings reveal the central role played in the anomalies of the Hall resistivity loops by electronic inhomogeneity of SrRuO 3 layers due to the interfacing with semimetallic 5d 5 SrIrO 3 .

Origin of the hump anomalies in the Hall resistance loops of ultrathin SrRuO3/SrIrO3 multilayers

“…The magnetic moment of the samples was measured as a function of temperature and magnetic field using a superconducting quantum interference device (SQUID) magnetometer (MPMS XL-7 from Quantum Design). The magnetic background due to the diamagnetic SrTiO 3 substrates was subtracted from the total magnetic re-sponse and often also corrections for a ferromagnetic impurity contribution had to be applied [35].…”

“…There exists very little insight in the interfacial DMI at epitaxial oxide interfaces [34], although hints for the existence of an interfacial DMI in SrIrO3 (2 uc)/SrRuO 3 (10 uc) bilayers were inferred from the analyses of the magnetic domain wall chirality [12]. We previously studied asymmetric SrZrO3/SrRuO3/SrIrO3 and SrHfO3/SrRuO3/SrZrO3 multilayers in which we aimed to observe the possible effects of the net interfacial DMI on the magnetotransport properties and magnetic domain formation [35]. However, these SrRuO 3 multilayers, with insulating spacers, were magnetically only very weakly coupled [36] and did not permit a conclusive investigation of the magnetic domains by magnetic force microscopy.…”

Angular dependence of Hall effect and magnetoresistance in SrRuO$_3$-SrIrO$_3$ heterostructures

“…Using a two channel anomalous Hall effect model we found in our symmetric [(SrRuO 3 ) 5 /(SrIrO 3 ) 2 )] k heterostructures that these anomalies do not originate from two independent spin-polarized conduction channels represented by anomalous Hall effects with different sign. Thus, we attribute these additional contributions to the topological Hall effect resulting from skyrmions in contrast to the asymmetric SrRuO 3 based heterostructures in [61], for which the total Hall effect could be modelled within the two-channel model. Temperature-dependent magnetoresistance with out-of-plane oriented magnetic field displays a crossover upon cooling below 60 K from positive to negative MR. To fit the MR we introduce a two channel MR model, comparable to the two channel anomalous Hall effect model with similar coercitive fields.…”

Magnetic interlayer coupling between ferromagnetic SrRuO$_3$ layers through a SrIrO$_3$ spacer

“…Recently, the ferromagnetic perovkite oxide SrRuO 3 attracted attention due to the proposal of the formation of Néel-type skyrmions when it is interfaced with the large spin-orbit coupling 5d oxide SrIrO 3 [10][11][12]. While the existence of topologically non-trivial textures in SrRuO 3based thin films remains controversial [13][14][15][16][17][18][19][20][21], epitaxial heterostructures composed of ferromagnetic oxide layers with perpendicular magnetic anisotropy separated by non-magnetic spacers are of general interest due to their versality in modifying the type and strength of the magnetic interlayer coupling for instance through variation of the spacer thickness or the interactions at the epitaxial interfaces of dissimilar oxides [2,22]. Strong ferromagnetic coupling of the SrRuO 3 layers was realized by introducing a 4 monolayers (MLs) thick * These two authors contributed equally.…”

“…Insulating SrTiO 3 spacers, 1.6 nm to 2.5 nm thick, were found to result also in weak coupling or in magnetic decoupling of two epitaxial SrRuO 3 layers [2,24]. The interlayer coupling was little investigated for SrRuO 3 layers interfaced with SrIrO 3 , although several studies focused on the discussion of the origin of unconventional features in the magnetotransport of SrRuO 3 /SrIrO 3 heterostructures and multilayers [13][14][15][16][17][18][19]. In our previous study [25], the interlayer coupling between SrRuO 3 layers separated by an asymmetric spacer of the strong spin-orbit couplling oxide SrIrO 3 and the large band gap insulator SrZrO 3 was addressed.…”