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 FePS3 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 ab planes, ferromagnetic chains antiferromagnetically coupled, is preserved, but the magnetic propagation vector is altered from k=(0,1,12) to k=(0,1,0), 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 MoreReceived 9 April 2020Revised 15 September 2020Accepted 28 October 2020DOI:https://doi.org/10.1103/PhysRevX.11.011024Published 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 SocietyPhysics Subject Headings (PhySH)Research AreasMagnetic orderMagnetic phase transitionsMagnetismQuantum phase transitionsPhysical Systems2-dimensional systemsAntiferromagnetsHoneycomb latticeMagnetic systemsMott insulatorsStrongly correlated systemsTechniquesMagnetic techniquesMethods in magnetismNeutron diffractionNeutron techniquesSusceptibility measurementsCondensed Matter, Materials & Applied Physics
Highlights
The study of low-dimensional magnetism has long been of great interest in fundamental condensed-matter physics and has led to numerous applications
We have succeeded in mapping out the pressuretemperature magnetic phase diagram of van der Waals honeycomb antiferromagnet FePS3: the first such study in the highly scrutinized TMPX3 materials
We find an initial flip and continuous strengthening in the interplanar exchange, which we discuss in terms of the previously observed shear structural transition in these materials at low pressures and a tuning from 2D to 3D character
Summary
The study of low-dimensional magnetism has long been of great interest in fundamental condensed-matter physics and has led to numerous applications. A complementary, and critical, approach is to tune the magnetic interactions from 2D to 3D by applying hydrostatic pressure—in a van der Waals material, applying pressure predominantly compresses the weakly bonded interplanar separation and pushes the lattice toward a 3D character. This approach can be viewed as moving from the “quasi-2D” starting point in the opposite direction to a thickness dependence study and addresses the same fundamental physics questions. The use of pressure as a tuning parameter unlocks a cleaner and more controllable approach to map complete phase diagrams than methods such as chemical substitution or uniaxial strains
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