ZrTe2/CrTe2: an epitaxial van der Waals platform for spintronics

The rapid discovery of two-dimensional (2D) van der Waals (vdW) quantum materials has led to heterostructures that integrate diverse quantum functionalities such as topological phases, magnetism, and superconductivity. In this context, the epitaxial synthesis of vdW heterostructures with well-controlled interfaces is an attractive route towards wafer-scale platforms for systematically exploring fundamental properties and fashioning proof-of-concept devices. We describe the synthesis by molecular beam epitaxy of a vdW heterostructure that interfaces two material systems of contemporary interest: a 2D ferromagnet (1T-CrTe₂) and a topological semimetal (ZrTe₂). These heterostructures are throughly characterized using a complete suite of in vacuo techniques such as angle resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy, as well as ex situ techniques, including high resolution transmission electron microscopy (HR-TEM), x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), polarized neutron reflectometry, magnetotransport, and spin torque ferromagnetic resonance. The HR-TEM, XPS, and XRD data show the stabilization of the 1T-CrTe₂ phase. The ARPES data from CrTe₂ and ZrTe₂ are consistent with first principles calculations. We find that one unit-cell (u.c.) thick 1T-CrTe₂ grown epitaxially on ZrTe₂ is a 2D ferromagnet with perpendicular magnetic anisotropy, indicated by a hysteretic anomalous Hall effect (AHE) loop. In thicker samples (12 u.c. thick CrTe₂), the AHE has characteristics that may arise from real-space Berry curvature. Finally, in bilayers with ultrathin CrTe₂ (3 u.c. thickness), we demonstrate current-driven magnetization switching in a full vdW topological semimetal/2D ferromagnet heterostructure device.

Work done in collaboration with Yongxi Ou, Wilson Yanez, Run Xiao, Max Stanley, Supriya Ghosh, Boyang Zheng, Wei Jiang, Yu-Sheng Huang, Timothy Pillsbury, Alex Grutter, Julie Borchers, Anthony Richardella, Chaoxing Liu, Tony Low, Vincent H. Crespi, and K. Andre Mkhoyan.