arXiv subjects

Yilin Evan Li

Publications and source records attributed to Yilin Evan Li.

3 recordsLinked to original sources

arXiv2026

Strain-Induced Relaxor Multiferroicity at Room Temperature in Hexaferrite BaFe12O19 Thin Films

Multiferroic materials that combine magnetic and electric order at room temperature are rare. Here, we demonstrate strain-induced room-temperature polar order in the ferrimagnetic hexaferrite BaFe12O19. First-principles calculations reveal a strain-tunable energy landscape with multiple competing dipolar configurations and predict that compressive strain favors polar distortions. Using an isostructural Sr1.03Ga10.81Mg0.58Zr0.58O19 substrate, we grow coherently strained BaFe12O19 films with 1.1% in-plane biaxial compression. Second-harmonic generation measurements demonstrate inversion-symmetry breaking and establish a strain-stabilized polar phase that persists to at least 1000 K. Multislice electron ptychography directly reveals enhanced off-centering of Fe3+ ions within the trigonal-bipyramidal sites of the strained films and spatially varying local polarization, demonstrating the formation of polar nanoregions. Path-integral Monte Carlo simulations further show that compressive strain suppresses quantum fluctuations and stabilizes these local polar distortions. Together, these results establish strain-engineered BaFe12O19 as a room-temperature relaxor multiferroic, in which robust ferrimagnetism coexists with nanoscale polar order. Our work demonstrates a route for transforming an incipient ferroelectric ferrimagnetic into a polar magnetic material through epitaxial strain.

cond-mat.mtrl-sci↗

arXiv2025

Control of out-of-plane anti-damping spin torque with a canted ferromagnetic spin source

To achieve efficient anti-damping switching of nanoscale magnetic memories with perpendicular magnetic anisotropy using spin-orbit torque requires that the anti-damping spin-orbit torque have a strong out-of-plane component. The spin anomalous Hall effect and the planar Hall effect spin current produced by a ferromagnetic layer are candidate mechanisms for producing such an out-of-plane anti-damping torque, but both require that the magnetic moment of the spin source layer be canted partly out of the sample plane at zero applied magnetic field. Here we demonstrate such a canted configuration for a ferromagnetic SrRuO3 layer and we characterize all vector components of the torque that it produces, including non-zero out-of-plane anti-damping torques. We verify that the out-of-plane spin component can be tuned by the orientation of magnetic moment, with significant contributions from both the spin anomalous Hall effect and the planar Hall effect spin current.

cond-mat.mes-hall↗

arXiv2025

Improper Ferroelectricity at the Monolayer Limit

Ultrathin ferroelectric films with out-of-plane polarization and high Curie temperatures are key to miniaturizing electronic devices. Most ferroelectrics employed in devices are proper ferroelectrics, where spontaneous polarization is the primary order parameter. Unfortunately, the Curie temperature of proper ferroelectrics is drastically reduced as the ferroelectric becomes thin; nearly all proper ferroelectrics need to be thicker than several unit cells. The absence of an ultrathin limit has been predicted, but not verified for improper ferroelectrics. These are ferroelectrics where the polarization emerges secondary to the primary order parameter, such as a structural distortion. Here we report improper ferroelectricity with an undiminished Curie temperature in a 0.75-unit-cell-thick hexagonal LuFeO3 (h-LuFeO3) film grown on a SrCo2Ru4O11 bottom electrode with an atomically engineered monolayer bridging layer. Our results demonstrate the absence of a critical thickness for improper ferroelectricity and provide a methodology for creating ultrathin improper ferroelectrics by stabilizing their primary order parameters.

cond-mat.mtrl-sci↗