Accessing new magnetic regimes by tuning the ligand spin-orbit coupling in van der Waals magnets

Abstract

Van der Waals (VdW) materials have opened new directions in the study of low dimensional magnetism. A largely unexplored arena is the intrinsic tuning of VdW magnets toward new ground states. Chromium trihalides provided the first such example with a change of interlayer magnetic coupling emerging upon exfoliation. Here, we take a different approach to engineer previously unknown ground states, not by exfoliation, but by tuning the spin-orbit coupling (SOC) of the nonmagnetic ligand atoms (Cl, Br, I). We synthesize a three-halide series, CrCl3 − x − yBrxIy, and map their magnetic properties as a function of Cl, Br, and I content. The resulting triangular phase diagrams unveil a frustrated regime near CrCl3. First-principles calculations confirm that the frustration is driven by a competition between the chromium and halide SOCs. Furthermore, we reveal a field-induced change of interlayer coupling in the bulk of CrCl3 − x − yBrxIy crystals at the same field as in the exfoliation experiments.

Manipulation of Magnetic Skyrmion in a 2D van der Waals Heterostructure via Both Electric and Magnetic Fields

“…As a typical 2D vdW magnet, CrCl 3 monolayer has a P−31m space group and consists of two Cl sublayers and one Cr sublayer on which the magnetic Cr 3+ ions form a honeycomb lattice; the magnetic moment is ≈3.0 μ B per Cr. [45,46] On a freestanding CrCl 3 monolayer, [47,48] the mag netic dipole-dipole interaction outweighs the perpendicular anisotropy induced by spin-orbit coupling, resulting in an easyplane anisotropy and merons (with a topological number Q = 1/2). The DMI is absent from these freestanding films due to the inversion symmetry.…”

Controlling magnetism through Ising superconductivity in magnetic van der Waals heterostructures

“…However, the magnitude of J depends on the chosen materials combination, and can also be below the critical field H P . In what follows, we consider a case of the induced exchange field J < H P in the monolayer TMD [9,46,47] so that it becomes superconducting at low enough temperature.…”

“…The direction of the exchange field is related to the magnetization direction of the ferromagnet, which is determined by the anisotropy energy. A monolayer ferromagnet such as CrI 3 [9] and CrBr 3 [47] shows a uniaxial anisotropy, and the anisotropy energy density can be written as…”

“…This relation is possible as the anisotropy energy of a monolayer ferromagnet can be tuned by various means. For example, the magnetic anisotropy can be engineered by strain [51] and by controlling the SOC via chemical tuning [47]. In other words, the anisotropic spin susceptibility leads to the switching of an off-plane easy axis anisotropy to the easy plane anisotropy if K eff < χ S J 2 /2.…”

“…A more interesting case takes place for ferromagnets with anisotropy constants with intermediate values [47]. In this case, the induced exchange field is out-of-plane at low temperature and in-plane at a higher temperature.…”