Electrically tunable high Curie temperature two-dimensional ferromagnetism in van der Waals layered crystals

Abstract

Identifying intrinsic low-dimensional ferromagnets with high magnetic transition temperature and electrically tunable magnetism is crucial for the development of miniaturized spintronics and magnetoelectrics. Recently, long-range 2D ferromagnetism was observed in van der Waals crystals CrI3 and Cr2Ge2Te6, however, their Curie temperature is significantly lowered when reducing down to monolayer/few layers. Herein, using renormalized spin-wave theory and first-principles electronic structure theory, we present a theoretical study of electrically tunable 2D ferromagnetism in van der Waals layered CrSBr and CrSeBr semiconductors with a high Curie temperature of ∼150 K and a sizable bandgap. The high transition temperature is attributed to the strong anion-mediated superexchange interaction and a sizable spin-wave excitation gap due to large exchange and single-ion anisotropy. Remarkably, hole and electron doping can switch the magnetization easy axis from the in-plane to the out-of-plane direction. These unique characteristics establish monolayer CrSBr and CrSeBr as a promising platform for realizing 2D spintronics and magnetoelectrics such as 2D spin valves and spin field effect transistors.

Electrical and thermal generation of spin currents by magnetic bilayer graphene

“…1c), which is an air-stable vdW semiconductor (bandgap of ~1.5 eV; see Supplementary Section 18 for transport measurements) with an interlayer AFM ordering up to a relatively high Néel temperature of T N ≈ 132 K (refs. [34][35][36][37] ). Furthermore, the antiferromagnetism promises ultrafast operations and robustness against external magnetic fields 38 and also is expected to be tunable by a gate electric field 35,39 .…”

“…[34][35][36][37] ). Furthermore, the antiferromagnetism promises ultrafast operations and robustness against external magnetic fields 38 and also is expected to be tunable by a gate electric field 35,39 . Mechanical cleavage of the CrSBr crystal results in flakes with a specific rectangular geometry that correlates with its in-plane magnetic anisotropy axes (Fig.…”

CrSbSe3: a pseudo one-dimensional ferromagnetic semiconductor

“…The LSDA plus Hubbard U (LSDA+U ) method [17,18] is used to describe the correlation effect of the Cr 3d electrons, with a common value of U =3 eV and Hund exchange J H =1 eV. Note that typically, U is about 3 eV for low-dimensional Cr-compounds [19][20][21]. J H is actually the difference of the energies of electrons with different spins or orbitals on a same atomic shell, and therefore, J H is almost not screened and not modified when going from an atom to a solid.…”

Triaxial magnetic anisotropy in the two-dimensional ferromagnetic semiconductor CrSBr

“…The bulk CrSBr has a triaxial MA with the easy magnetization b-axis, the intermediate a-axis and the hard c-axis [19]. Several theoretical studies predict CrSBr monolayer to be a 2D FM with T C of 160 ∼ 180 K [20][21][22][23]. Experimentally, the T C was measured to be 146 K for CrSBr monolayer very recently by the second harmonic generation technique [24].…”

“…Experimentally, the T C was measured to be 146 K for CrSBr monolayer very recently by the second harmonic generation technique [24]. In contrast to the well studied intralayer FM coupling and the 2D FM order [20][21][22][23][24], the triaxial MA [19] received much less attention previously, which is however indispensable for the 2D magnetic order. Moreover, compared with an SOC induced MA, a shape anisotropy due to the magnetic dipole-dipole interaction is often relatively weak and of less concern.…”