APS New England Section (NES) Annual Meeting 2025
Friday–Saturday, November 7–8, 2025;
Brown University, Providence, Rhode Island
Session H01: Condensed Matter Physics IV
11:00 AM–1:00 PM,
Saturday, November 8, 2025
Brown University
Room: Pembroke Hall: Room 305
Chair: Ilija Nikolov, Brown University
Abstract: H01.00007 : Room Temperature Switchable Ferroelectricity and Topological Multiferroic Textures in Ultrathin BiFeO3
12:36 PM–12:48 PM
Abstract
Presenter:
George A Fratian
(Brown University)
Author:
George A Fratian
(Brown University)
BiFeO3 (BFO) is a well studied room-temperature magnetoelectric with a large ferroelectric polarization and canted G-type antiferromagnetic ordering arising from the Dzyaloshinskii-Moriya interaction. It holds significant promise in low-energy computing owing to its demonstrated reliable switching performance in thin films, but scaling to thinner thickness is required for applications in low power computing. However, scaling order parameters to the ultrathin thicknesses is difficult because polar order vanishes due to uncompensated bound charges at the ferroelectric surface, causing “dead layer” formation. Moreover, dead layers also commonly form in ultrathin antiferromagnets due to off-stoichiometry or loss in magnetic anisotropy. To overcome these limitations our group has synthesized a thickness series of high-quality BFO films down to 4 unit cells under boundary conditions conducive to stabilizing multiferroic order via compressive strain and short-circuit conditions. To achieve this, we have deposited BFO atop SrRuO3 (SRO) – a conductive perovskite – to combat the depolarizing fields which is further grown on DyScO3 to introduce a compressive (~1%) strain. Strikingly, under these conditions, we find that the polarization rotates from the <111> direction to almost the <001> pseudocubic direction indicating a structural phase transition from rhombohedral (R) to tetragonal-like (T – like). Perhaps most fascinatingly, in our thinnest sample, we discover the persistence of a single-unit cell thick polar displacement. We also demonstrate that the sample remains magnetic and PFM box-in-box measurements corroborate the persistence of the polar order. Furthermore, during this phase transition, our group has captured the persistence of the magnetic cycloid in BFO down to a thickness of 3.5nm using XMLD-PEEM at MAXIV. There, interesting topological multiferroic textures are observed as BFO undergoes frustration owing to its continuous phase transformation from R to T-like. Below 3.5nm the cycloid disappears and the magnetism turns collinear prompting possibilities of an altermagnetic state. Recent theoretical work outlines the conditions for BFO to exhibit altermagnetic behavior and our samples indicate a possibility of that signal but more work is needed.