Researchers at Helmholtz-Zentrum Berlin (HZB), KAIST, the Technical University of Munich, the Max Planck Institute for Chemical Physics of Solids, the Technical University of Dresden, the Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, the Paul Scherrer Institut's Swiss Light Source, and RIKEN's Center for Emergent Matter Science have shown that magnetic fields of just a few millitesla, applied in-plane rather than perpendicular to a sample, can continuously rotate and reshape the chiral magnetic stripe domains of a room-temperature noncentrosymmetric magnet, offering a new vector-field-based way to control magnetic domain orientation.
Micromagnetic simulations show how a small magnetic field in plane with the magnetic stripes can change the magnetic texture from a stripe pattern to a fan pattern. Image credit: HZB
Noncentrosymmetric magnets, which lack inversion symmetry, host a competition between conventional exchange interaction and the antisymmetric Dzyaloshinskii-Moriya interaction (DMI), the effect responsible for the chirality of textures such as helices, cycloids, and skyrmions. How that competition plays out depends heavily on a material's crystal symmetry, and most experimental work on it has relied on Lorentz transmission electron microscopy (LTEM), a technique generally limited to magnetic field tilt angles of 45 degrees or less. That has left the response of these materials to genuinely in-plane fields, and the role of a material's full three-dimensional field environment, largely unexplored.
The team studied a thin lamella of (Fe0.63Ni0.3Pd0.07)3P, a tetragonal, S4-symmetric compound known as FNPP that hosts room-temperature antiskyrmions, using resonant small-angle X-ray scattering (SAXS) at HZB's VEKMAG instrument at the BESSY II synchrotron, a vector magnet capable of applying up to 1 tesla in any spatial direction, alongside soft X-ray ptychography at the MAXYMUS microscope for real-space imaging. With the field applied along the sample's out-of-plane axis, the material's zero-field chiral stripe domains progressed through a soliton-lattice state and into a single-domain hexagonal skyrmion lattice as field strength increased. Switching to an in-plane field produced a different effect entirely: at room temperature, a field of only about 10 millitesla was enough to collapse the stripe domains into a pair of spots oriented perpendicular to the field direction, converting the chiral stripe pattern into an achiral "fan" configuration as the Zeeman energy of the aligned state overcame the DMI-driven chiral twisting. Rotating the in-plane field's direction continuously rotated the fan orientation with it, and removing the field afterward restored the original stripe orientation along the crystal's ⟨110⟩ axes.
Cooling the sample changed that behavior substantially. At 100 K and above, the stripe domains still reverted to their original orientation once a training field was removed, but at 50 K and below, the domains instead retained the orientation set by the last applied field, revealing a metastable directional memory effect. The team also found that a fourfold anisotropy in the stripe periodicity, negligible at 50 K, grew roughly tenfold by 20 K, together with a gradual rotation of the material's effective DMI axis by up to 30 degrees. A theoretical model combining DMI, magnetocrystalline anisotropy, and anisotropic exchange interaction reproduced this temperature evolution, attributing the low-temperature anisotropy growth primarily to a strengthening anisotropic exchange interaction rather than to the increase in magnetization alone.
"Even a very small field of just 10 millitesla was sufficient to transform a chiral stripe configuration into an achiral fan configuration," said HZB's Dr. Victor Ukleev, the study's lead author. Describing the mechanism behind the effect, he added that the team's experiments and modeling revealed "how a weak in-plane B-field establishes an equilibrium between these interactions, thereby altering the stripe state." The vector-field measurements were made possible by VEKMAG, described by HZB as a globally unique instrument developed by Dr. Florin Radu's team.
The authors describe their work as providing the first explicit analytical framework linking DMI, anisotropic exchange, and vector-field-driven domain reconfiguration in tetragonal noncentrosymmetric magnets, and frame the demonstrated directional memory effect and millitesla-scale field sensitivity as a step toward using vector magnetic fields to manipulate mesoscale magnetic textures in functional materials for energy-efficient magnetic memory devices.