Abstract
Layered van der Waals 2D magnetic materials are of great interest in fundamental condensed-matter physics research, as well as for potential applications in spintronics and device physics. We present neutron powder diffraction data using new ultrahigh-pressure techniques to measure the magnetic structure of Mott-insulating 2D honeycomb antiferromagnet at pressures up to 183 kbar and temperatures down to 80 K. These data are complemented by high-pressure magnetometry and reverse Monte Carlo modeling of the spin configurations. As pressure is applied, the previously measured ambient-pressure magnetic order switches from an antiferromagnetic to a ferromagnetic interplanar interaction and from 2D-like to 3D-like character. The overall antiferromagnetic structure within the planes, ferromagnetic chains antiferromagnetically coupled, is preserved, but the magnetic propagation vector is altered from to , a halving of the magnetic unit cell size. At higher pressures, coincident with the second structural transition and the insulator-metal transition in this compound, we observe a suppression of this long-range order and emergence of a form of magnetic short-range order which survives above room temperature. Reverse Monte Carlo fitting suggests this phase to be a short-ranged version of the original ambient-pressure structure—with the Fe moment size remaining of similar magnitude and with a return to antiferromagnetic interplanar correlations. The persistence of magnetism well into the HP-II metallic state is an observation in contradiction with previous x-ray spectroscopy results which suggest a spin-crossover transition.
1 More- Received 9 April 2020
- Revised 15 September 2020
- Accepted 28 October 2020
DOI:https://doi.org/10.1103/PhysRevX.11.011024
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Imagine using the same pencil for writing on paper as well as on a specially designed screen. Such a “magic material” could be mechanically flexible and form a new kind of circuit for storing information and performing computation. Welcome to the world of “magnetic graphene,” which also changes its properties drastically when put under pressure or strain. Here, we present the first high-pressure neutron study of an example of magnetic graphene, , which transitions from an insulator to a metal when compressed.
This class of magnetic materials offers new routes to understanding the physics of novel magnetic states and superconductivity. Through the deployment of revolutionary high-pressure techniques, we have unveiled the evolution of magnetic ordering in through its insulator-metal transition and into the unconventional metallic state.
These first-of-their-kind measurements have uncovered exotic new states and behaviors. We suspect that this newly discovered high-pressure magnetic phase most likely forms a precursor to superconductivity.