Atomic-scale control of magnetic anisotropy via novel spin–orbit coupling effect in La _2/3 Sr _1/3 MnO ₃ /SrIrO ₃ superlattices

Abstract

Magnetic anisotropy (MA) is one of the most important material properties for modern spintronic devices. Conventional manipulation of the intrinsic MA, i.e., magnetocrystalline anisotropy (MCA), typically depends upon crystal symmetry. Extrinsic control over the MA is usually achieved by introducing shape anisotropy or exchange bias from another magnetically ordered material. Here we demonstrate a pathway to manipulate MA of 3d transition-metal oxides (TMOs) by digitally inserting nonmagnetic 5d TMOs with pronounced spin-orbit coupling (SOC). High-quality superlattices comprising ferromagnetic La 2/3 Sr 1/3 MnO 3 (LSMO) and paramagnetic SrIrO 3 (SIO) are synthesized with the precise control of thickness at the atomic scale. Magnetic easy-axis reorientation is observed by controlling the dimensionality of SIO, mediated through the emergence of a novel spin-orbit state within the nominally paramagnetic SIO.complex oxides | interfacial physics | magnetic anisotropy | emergent magnetism | strong spin-orbit coupling M agnetic anisotropy (MA) is one of the fundamental properties of magnetic materials. The widespread scientific interest in MA originates from its decisive role in determining a rich spectrum of physical responses, such as the Kondo effect (1), the magnetocaloric effect (2), magnetic skyrmions (3), etc. From a technological viewpoint, it is an important and promising approach to control MA by external stimuli, such as electric field (4). In general, there are two approaches to design MA of a ferromagnet. In the first approach one manipulates the intrinsic magnetocrystalline anisotropy (MCA), deriving from the local crystal symmetry and spin-orbit coupling (SOC) of the magnetic ion (5-7). Alternatively, one can tune the MA through extrinsic contributions to the anisotropy such as shape (8) or exchange coupling to a strong antiferromagnet (9).One focus of magnetism research is 3d transition-metal oxides (TMOs), a class of materials that exhibit various functionalities including ferromagnetism due to the strong electron-electron correlation. However, SOC is usually weak or negligible in 3d TMOs. On the other hand, the pronounced SOC of heavy elements has drawn attention in recent years due to the emergence of new topological states of matter (10-12) and spintronics (13,14). In contrast to 3d TMOs, the correlation strength is often too small in 5d TMOs to host magnetism. Therefore, it is an interesting approach to design systems that combine the merits of these two fundamental interactions. A similar ideal has been studied in metal multilayers (15, 16). However, it still remains an important challenge to explore the ideal in complex oxides, where a variety of emergent phenomena have been discovered due to the power of atomic-scale confinement and interfacial coupling (17-21).Here we present an approach toward accomplishing this goal by atomic-scale synthesis. By fabricating high-quality superlattices comprising 3d and 5d TMOs, we address two open questions: the effect of SOC on the functionality of 3d TMOs an...

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“…Representative results are shown in Fig. 1(b) and are similar to spectra from previous reports [23,24]. These results reveal several aspects of magnetism in the SLs.…”

“…Secondly, the small induced magnetization in SIO couples antiparallel to the moments of LSMO [23,24]. Thirdly, the same sign and comparable amplitude of the XMCD signal at the Ir L 2 and L 3 edges indicate a large contribution from orbital moments [23,24]. Finally, the emergent ferromagnetism in Sr-rich SLs is due to a charge transfer effect at the interface [24], which has been observed in other systems [25][26][27].…”

“…S3). Secondly, the small induced magnetization in SIO couples antiparallel to the moments of LSMO [23,24]. Thirdly, the same sign and comparable amplitude of the XMCD signal at the Ir L 2 and L 3 edges indicate a large contribution from orbital moments [23,24].…”

Interface-induced phenomena in magnetism

“…Tuning multiple interfacial properties provides a powerful route to access novel states, as illustrated by work on vanadate superlattices, in which ferromagnetism is predicted to emerge by simultaneously engineering octahedral rotations and bandfilling in LaVO 3 /SrVO 3 superlattices [Dang and Millis, 2013]. Oxide analogues of ferromagnet/heavy metal heterostructures that incorporate strongly spin-orbit coupled 5 d iridium-based oxides, such as ferromagnetic La 0.67 Sr 0.33 MnO 3 /paramagnetic metal SrIrO 3 [Yia et al ., 2016], may enable novel interfacial magnetic properties arising from the combination of narrow electron bands, strong correlation effects, and significant spin-orbit coupling.…”

Enhanced Magnetic Anisotropy and Orbital Symmetry Breaking in Manganite Heterostructures

“…As one of the most studied ferromagnetic oxides, La 2/3 Sr 1/3 MnO 3 (LSMO) has extensively served as a platform to advance the understanding and control on magnetic anisotropy in complex oxides. Yi et al demonstrated a large perpendicular magnetic anisotropy in LSMO heterostructures modified by a SrIrO 3 layer with a strong spin–orbit coupling . Rajapitamahuni et al used a ferroelectric PbZr 0.2 Ti 0.8 O 3 layer to tune the Mn 3d orbital occupancy in an adjacent La 0.8 Sr 0.2 MnO 3 layer to obtain a 22% improvement on lateral magnetic anisotropy energy (MAE) .…”