Morphogenesis of Spin Cycloids in a Non-collinear Antiferromagnet

arXiv (Cornell University) · 2024 · 1 citations

• Condensed matter physics
• Physics
• Biology

Pattern formation in spin systems with continuous-rotational symmetry (CRS) provides a powerful platform to study emergent complex magnetic phases and topological defects in condensed-matter physics. However, its understanding and correlation with unconventional magnetic order along with high-resolution nanoscale imaging is challenging. Here, we employ scanning NV magnetometry to unveil the morphogenesis of spin cycloids at both the local and global scales within a single ferroelectric domain of (111)-oriented BiFeO$_3$ (which is a non-collinear antiferromagnet), resulting in formation of a glassy labyrinthine pattern. We find that the domains of locally oriented cycloids are interconnected by an array of topological defects and exhibit isotropic energy landscape predicted by first-principles calculations. We propose that the CRS of spin-cycloid propagation directions within the (111) drives the formation of the labyrinthine pattern and the associated topological defects such as antiferromagnetic skyrmions. Unexpectedly, reversing the as-grown ferroelectric polarization from [$\bar{1}$$\bar{1}$$\bar{1}$] to [111] induces a magnetic phase transition, destroying the labyrinthine pattern and producing a deterministic non-volatile non cycloidal, uniformly magnetized state. These findings highlight that (111)-oriented BiFeO$_3$ is not only important for studying the fascinating subject of pattern formation but could also be utilized as an ideal platform for integrating novel topological defects in the field of antiferromagnetic spintronics.

Antiferromagnetic half-skyrmions and bimerons at room temperature

Nature · 2021 · 198 citations

• Condensed matter physics
• Physics
• Materials science

In the quest for post-CMOS technologies, ferromagnetic skyrmions and their\nanti-particles have shown great promise as topologically protected solitonic\ninformation carriers in memory-in-logic or neuromorphic devices. However, the\npresence of dipolar fields in ferromagnets, restricting the formation of\nultra-small topological textures, and the deleterious skyrmion Hall effect when\ndriven by spin torques have thus far inhibited their practical implementations.\nAntiferromagnetic analogues, which are predicted to demonstrate relativistic\ndynamics, fast deflection-free motion and size scaling have recently come into\nintense focus, but their experimental realizations in natural antiferromagnetic\nsystems are yet to emerge. Here, we demonstrate a family of topological\nantiferromagnetic spin-textures in $\\alpha$-Fe$_2$O$_3$ - an earth-abundant\noxide insulator - capped with a Pt over-layer. By exploiting a first-order\nanalogue of the Kibble-Zurek mechanism, we stabilize exotic merons-antimerons\n(half-skyrmions), and bimerons, which can be erased by magnetic fields and\nre-generated by temperature cycling. These structures have characteristic sizes\nin the range ~100 nm that can be chemically controlled via precise tuning of\nthe exchange and anisotropy, with pathway to further scaling. Driven by\ncurrent-based spin torques from the heavy-metal over-layer, some of these AFM\ntextures could emerge as prime candidates for low-energy antiferromagnetic\nspintronics at room temperature.

Heterogeneous integration of single-crystalline complex-oxide membranes

Nature · 2020 · 348 citations

• Materials science
• Nanotechnology
• Optoelectronics

Controlling spin current polarization through non-collinear antiferromagnetism

Nature Communications · 2020 · 197 citations

• Condensed matter physics
• Physics
• Quantum mechanics

The interconversion of charge and spin currents via spin-Hall effect is essential for spintronics. Energy-efficient and deterministic switching of magnetization can be achieved when spin polarizations of these spin currents are collinear with the magnetization. However, symmetry conditions generally restrict spin polarizations to be orthogonal to both the charge and spin flows. Spin polarizations can deviate from such direction in nonmagnetic materials only when the crystalline symmetry is reduced. Here, we show control of the spin polarization direction by using a non-collinear antiferromagnet Mn3GaN, in which the triangular spin structure creates a low magnetic symmetry while maintaining a high crystalline symmetry. We demonstrate that epitaxial Mn3GaN/permalloy heterostructures can generate unconventional spin-orbit torques at room temperature corresponding to out-of-plane and Dresselhaus-like spin polarizations which are forbidden in any sample with two-fold rotational symmetry. Our results demonstrate an approach based on spin-structure design for controlling spin-orbit torque, enabling high-efficient antiferromagnetic spintronics.