Switching 2D magnetic states via pressure tuning of layer stacking

Abstract

The physical properties of two-dimensional van der Waals (2D vdW) crystals depend sensitively on the interlayer coupling, which is intimately connected to the stacking arrangement and the interlayer spacing. For example, simply changing the twist angle between graphene layers can induce a variety of correlated electronic phases 1-8 , which can be controlled further in a continuous manner by applying hydrostatic pressure to decrease the interlayer spacing 3 . In the recently discovered 2D magnets 9,10 , theory suggests that the interlayer exchange coupling strongly depends on layer separation, while the stacking arrangement can even change the sign of the magnetic exchange, thus drastically modifying the ground state 11-15 . Here, we demonstrate pressure tuning of magnetic order in the 2D magnet CrI3. We probe the magnetic states using tunneling 16,17 and scanning magnetic circular dichroism microscopy measurements 10 . We find that the interlayer magnetic coupling can be more than doubled by hydrostatic pressure. In bilayer CrI3, pressure induces a transition from layered antiferromagnetic to ferromagnetic phases. In trilayer CrI3, pressure can create coexisting domains of three phases, one ferromagnetic and two distinct antiferromagnetic. The observed changes in magnetic order can be explained by changes in the stacking arrangement. Such coupling between stacking order and magnetism provides ample opportunities for designer magnetic phases and functionalities. discussion.

Low-temperature monoclinic layer stacking in atomically thin CrI3 crystals

“…This picture is in agreement with recent measurements on few-layer CrI 3 where either an accidental puncture 14 or an external pressure 25,26 provided the energy to undergo a structural transformation with a corresponding transition to FM ordering. Additional validations supporting the connection between crystal structure and magnetism have been achieved in a related material, CrBr 3 , by observing different magnetic ordering associated with novel stacking patterns (not corresponding to the bulk phases) in bilayers grown by molecular beam epitaxy 27 .…”

Coexistence of Magnetic Orders in Two-Dimensional Magnet CrI3

“…Bulk CrI3 is in a monoclinic phase at room temperature and undergoes a structural phase transition to a rhombohedral phase at around 200 K. 14,25 The main difference between the two phases is different stacking orders of the CrI3 layers. Second harmonic generation 13 , high pressure 17,18 , and Raman 19 experiments demonstrate that exfoliated few-layer CrI3 flakes remain in the monoclinic phase at all temperatures. Given the similarity in magnetic properties between the surface layer group in our samples and few-layer CrI3 flakes, and between the inner layer group and CrI3 bulk crystals, we believe that the surface layers, which is about ~13 nm thick at each surface, should be in the monoclinic phase at all temperatures like few-layer CrI3 flakes, while the inner layers undergo the structural phase transition like bulk CrI3.…”

Two-dimensional van der Waals spinterfaces and magnetic-interfaces

“…A recent report on a few nm thick 2D CrCl 3 crystal showed a ten-fold enhancement of the interlayer exchange coupling compared to bulk CrCl 3 due to the intrinsically different stacking order 133 . Change of interlayer stacking order also results in a shift in the magnetic state from FM to AFM, as observed in CrI 3 while using hydrostatic pressure to tune the interlayer distance and arrangment 134 . Similarly, distinct interlayer magnetism was also observed in bilayer CrBr 3 by spin-polarized scanning tunneling spectroscopy, where measurements revealed antiferromagnetic coupling in rhombohedral stacking while ferromagnetic coupling in monoclinic layer stacking 135 .…”