Kinetically Controlled Epitaxial Growth of Fe3GeTe2 van der Waals Ferromagnetic Films

TLDR: In this article , the authors demonstrate that kinetics play an important role in the epitaxial growth of Fe 3 GeTe 2 (FGT) van der Waals (vdW) ferromagnetic fi lms by molecular beam epitaxy.

Abstract: : We demonstrate that kinetics play an important role in the epitaxial growth of Fe 3 GeTe 2 (FGT) van der Waals (vdW) ferromagnetic fi lms by molecular beam epitaxy. By varying the deposition rate, we control the formation or suppression of an initial tellurium-de fi cient non-van-der-Waals phase (Fe 3 Ge 2 ) prior to realizing epitaxial growth of the vdW FGT phase. Using cross-sectional scanning transmission electron microscopy and scanning tunneling microscopy, we optimize the FGT fi lms to have atomically smooth surfaces and abrupt interfaces with the Ge(111) substrate. The magnetic properties of our high quality material are con fi rmed through magneto-optic, magnetotransport, and spin-polarized STM studies. Importantly, this demonstrates how the interplay of energetics and kinetics can help tune the re-evaporation rate of chalcogen atoms and interdi ff usion from the underlayer, which paves the way for future studies of van der Waals epitaxy. of 5 K. Spin-polarized STM measurements utilized a Cr tip and an out-of-plane magnetic fi eld. We performed AHE and MCD measurements in an Oxford Spectromag magneto-optical cryostat. To obtain out-of-plane hysteresis loops, we applied a magnetic fi eld perpendicular to the surface of the sample. The AHE measurements were performed using lock-in detection at 987 Hz and an excitation current of 100 μ A (rms). For MCD measurements, we utilized a 100 μ W, 532 nm laser beam focused to a spot size of ∼ 150 μ m. The helicity of the incident beam was modulated at 50 kHz by a photoelastic modulator and the MCD of the re fl ectivity was measured using an ampli fi ed Si photodiode and lock-in detection. structural quality of the surface and interface. The excellent magnetic properties with square out-of-plane hysteresis loops is con fi rmed by AHE, MCD, and spin-polarized STM measurements. Our results reveal an important way to think about and optimize MBE growth, leading to potentially better 2D materials.