Evolution of interlayer and intralayer magnetism in three atomically thin chromium trihalides

Abstract

We conduct a comprehensive study of three different magnetic semiconductors, CrI3, CrBr3, and CrCl3, by incorporating both few-and bi-layer samples in van der Waals tunnel junctions. We find that the interlayer magnetic ordering, exchange gap, magnetic anisotropy, as well as magnon excitations evolve systematically with changing halogen atom. By fitting to a spin wave theory that accounts for nearest neighbor exchange interactions, we are able to further determine a simple spin Hamiltonian describing all three systems. These results extend the 2D magnetism platform to Ising, Heisenberg, and XY spin classes in a single material family. Using magneto-optical measurements, we additionally demonstrate that ferromagnetism can be stabilized down to monolayer in more isotropic CrBr3, with transition temperature still close to that of the bulk.

Enhancement of the Magnetic Coupling in Exfoliated CrCl3Crystals Observed by Low‐Temperature Magnetic Force Microscopy and X‐ray Magnetic Circular Dichroism

“…The effect was independently observed both on ensembles of CrCl 3 flakes by conventional SQUID magnetometry and surface selective synchrotron‐based XMCD experiments, and on individual flakes by low‐temperature MFM. These observations are in agreement with recent studies conducted with magnetotransport in tunneling junctions [ 21,28,29,48 ] and magneto‐optical measurements, [ 28 ] which highlighted that ultrathin flakes of chromium trihalides exhibit different magnetic interactions compared to the pristine bulk crystals.…”

“…We use low‐temperature magnetic force microscopy (MFM), as a local magnetic probe, flanked by angle‐resolved X‐ray magnetic circular dichroism (XMCD) and superconducting quantum interference device (SQUID) magnetometry. While previous studies focused on the magnetism of ultrathin flakes (<9 nm), [ 21,28,29 ] our multitechnique study presents a detailed characterization of pristine and exfoliated CrCl 3 in the thickness range ≈10–50 nm. Our results show that micromechanical cleavage determines, even at the mesoscopic thickness of 10–50 nm thickness—a scale of technological relevance—a significant change in the magnetic properties of the CrCl 3 crystal.…”

Magnetic Proximity Effect in Graphene/CrBr3 van der Waals Heterostructures

“…Since the magnetic exchange field is nearly irrelevant to the external field B ⊥ ,when the applied field is low and less than about 1 T, the line slope is a bit steeper than the one with field larger than 1 T, which demonstrates that magnetic exchange field is the dominating contribution to the nonlocal resistance at low field. Giving μ 0 H = 4 T, the estimate B Z is approximately twice of the applied field, which seems weaker than other reported 2D or graphene/ferromagnetic material systems (Table S2, Supporting Information) like WSe 2 /EuS, [ 52 ] graphene/EuS, [ 12 ] and graphene/BiFeO 3 , [ 13 ] but this result is reasonable, because 2D CrBr 3 has a smaller interlayer exchange coupling energy J = 1.56 meV, [ 53 ] and its magnetic moment per Cr ion is 3.25 μ B , [ 54 ] comparing with EuS which has an exchange coupling energy J ≈ 10 meV, and the magnetic moment per Eu ion is 7.9 μ B . [ 55 ]…”

Artificial Multiferroics and Enhanced Magnetoelectric Effect in van der Waals Heterostructures

“…[20][21][22] Meanwhile, 2D ferromagnetism has been recently achieved in vdW materials, such as few-layer Cr2Ge2Te3, 23 CrI3, 24 and Fe3GeTe2, 25,26 spurring substantial interests to fabricate ultra-thin magnetic devices and study fundamental properties, such as magnons, spin liquids, and many other quantum states in reduced-dimensional structures. [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44] All these advances pave the way for exploring the existence of 2D multiferroics and magnetoelectronic couplings.…”