In traditional tiled lattice structures, simple magnetic ordering configurations typically exhibit collinear spin arrangements, primarily driven by Heisenberg exchange interactions. However, with the rapid advancement of micro/nanofabrication technologies, low-dimensional curved geometries capable of breaking spatial inversion symmetry have attracted significant research interest. This curvature effect, combined with the spontaneous breaking of time-reversal symmetry in magnetic materials, can induce non-collinear spin textures such as magnetic vortices, hopfions, and skyrmions. These complex magnetic structures show great potential for fundamental physics research and the development of next-generation high-density non-volatile memories and spintronic devices. Researchers have explored various magnetic configurations on curved surfaces, aiming to leverage geometric design to achieve topological magnetism and chiral magnetic states, thereby opening new pathways for the design of novel electronic materials.

Despite significant progress in this field, current research still faces serious challenges, particularly in exploring radial magnetism in high-quality crystalline curved structures. In most previous studies, the materials used were predominantly amorphous or polycrystalline. Due to the large geometric demagnetizing field, the magnetic easy axis of the films tends to lie in the in-plane direction, making it difficult to achieve an ideal radial distribution. Furthermore, how to precisely control lattice stress during the bending process while maintaining high crystalline quality remains a key technical challenge for fabricating high-performance microstructured devices.

To address the above issues, a research team composed of the Institute of Physics, Chinese Academy of Sciences, the University of Chinese Academy of Sciences, Tsinghua University, and the Songshan Lake Materials Laboratory conducted systematic studies using ZEPTOOLS' DMD maskless aligner. By leveraging the anisotropic interfacial stress self-assembly technique in SrTiO3/SrRuO3 bilayers, the team achieved, for the first time, the precise fabrication of radially curved magnetic configurations and the investigation of magnetoelectric transport mechanisms in high-crystalline-quality SrRuO3 microtubes.

Title: Strain‐Assembled Crystalline SrRuO3 Microtube and Emergent Curvilinear Magnetism
Journal: Advanced Science
URL: doi.org/10.1002/advs.20

The research team successfully fabricated an epitaxial bilayer thin-film heterostructure of strontium titanate and strontium ruthenate with high crystalline quality on a strontium titanate substrate using pulsed laser deposition. By cleverly introducing a twenty-nanometer-thick strontium cobaltite sacrificial layer and tuning the lattice mismatch between the epitaxial layers, a specific interfacial strain energy was pre-stored within the film. Through precise selection of the substrate crystal orientation, the researchers achieved anisotropic control of the strain distribution, thereby laying the physical foundation for the subsequent release of strain energy to drive self-rolling of the film into micrometer-scale tubular structures.

In the key steps of micro/nanofabrication, the researchers first used ZEPTOOLS' DMD maskless aligner to perform millimeter-scale localized patterning of the heterojunction thin films, followed by precise definition of rectangular or disk-shaped microstructural units via ion beam etching. After selectively removing the sacrificial layer with an acidic solution, the pre-strained epitaxial bilayer films spontaneously rolled up along specific crystallographic axes, ultimately forming microtubes with tunable diameters ranging from submicron to tens of micrometers. This fabrication process not only ensures that the curved structures maintain extremely high crystalline quality but also overcomes the limitations of traditional methods in forming complex three-dimensional geometries through strain-assisted self-assembly.

The experiments comprehensively characterized the magnetic properties of the microtube arrays using a superconducting quantum interference device (SQUID). The results confirmed that the strontium ruthenate films exhibit a unique radial magnetic configuration after rolling. Due to the strong spin-orbit coupling in the strontium ruthenate crystal and the resulting magnetocrystalline anisotropy, the magnetic easy axis remains always perpendicular to the film surface, which in the microtube geometry manifests as a continuous rotation of the magnetic moment along the radial direction. This radially symmetric rotating magnetic order shows a normalized remanent magnetization of approximately 63.7% under zero field, a value that is in excellent agreement with theoretical model predictions, strongly demonstrating that the research team successfully constructed a pure radial curved magnetism system.

To gain a deeper understanding of the influence of curvature on electron scattering mechanisms, the research team performed temperature- and angle-dependent magnetoresistance transport measurements on individual microtubes. By treating the microtube as an equivalent assembly of numerous longitudinally arranged planar thin-film strips, the researchers established an integral physical model that successfully simulated the intrinsic relationship between the overall resistance of the microtube and the local magnetic moment distribution. The study revealed that the anisotropic magnetoresistance effect in the microtube is not only related to the external magnetic field but also more profoundly reflects the preservation of lattice rotational symmetry in curved space and its modulation of charge transport. This achievement provides critical experimental evidence and theoretical support for the design of novel spintronic devices based on three-dimensional curved magnetic configurations.

ZEPTOOLS ZML series is a DMD-based maskless aligner that uses DMD to replace traditional photomasks, enabling rapid and flexible design of lithography patterns. It supports 2D and 8-bit grayscale lithography, meeting arbitrary micron-scale lithography requirements, and is widely used in MEMS, microfluidics, and many other fields.