Molecular Beam Epitaxy Grown Cr₂Te₃ Thin Films with Tunable Curie Temperatures for Spintronic Devices

Abstract

Materials with perpendicular magnetic anisotropy (PMA) effect with high Curie temperature is essential in applications. Cr2Te3 is a material that demonstrates PMA effect but with a relatively low Curie temperature of about 180 K. In this work, Cr 2 Te 3 thin films with Curie temperature ranging from 165 K to 295 K were successfully grown on Al2O3 by the molecular beam epitaxy (MBE) technique. To study the physical origin of the improved Curie temperature, structural analysis, magneto-transport and magnetic characterizations were conducted and analyzed in detail. In particular, the n-type feature of these thin films shows that they are an electron-enriched material. Ferromagnetic (FM) ordering and Anti Ferromagnetic (AFM) ordering competition were systematically investigated by magnetization characterizations. A 2 phenomenological model based on the degree of coupling between FM and AFM ordering was proposed to explain the observed Currie temperature enhancement in our samples. These findings indicate that the Curie temperature of Cr 2 Te 3 thin films can be tuned and our material could act as a novel magnetic material with potential for various magnetic applications.

Two‐dimensional magnetic transition metal chalcogenides

“…With different amounts of Cr vacancies in the intercalated Cr layers, a range of Cr m X n with different stoichiometric ratios, such as CrX, Cr 2 X 3 , Cr 3 X 4 , Cr 5 X 8 , and CrTe 2 , can be formed, and behave as ferrimagnetic, antiferromagnetic, and ferromagnetic. Epitaxial Cr 2 S 3 , 58 CrSe, 56 CrTe 2 , 59 CrTe, 60 and Cr 2 Te 3 61–63 thin films with thicknesses down to several nanometers have been grown on various substrates (mica, SrTiO 3 , Si, Bi 2 Se 3 , and so on) by CVD and MBE, showing high Curie temperature T c (e.g., ~305 K for 8.7 nm CrTe 2 thin film 59 ), and promising electrical transport properties (e.g., unconventional anomalous Hall effect 60 ) for spintronic devices. The successful synthesis of 2D Cr 2 S 3 , 55,58 Cr 2 Te 3 , 57 and CrTe 2 26 with ML thickness (referring to the smallest repeating unit along the z ‐direction) have also been recently reported.…”

“…Furthermore, room‐temperature ferromagnetism has also been observed in 2D Cr 2 Te 3 (Figure 3J–M​​​​), confirmed by anomalous Hall effect measurements (Figure 3L). 63 Interestingly, the transition temperature of the ferromagnetism phase ( T c ) increases from 160 K in the Cr 2 Te 3 thick film (40.3 nm) to 280 K in the thin film (7.1 nm). Although the synthesis of 1‐ and 2‐unit‐cell Cr 2 Te 3 has been achieved (Figure 3K), precise characterization of their magnetic properties is lacking due to poor stability.…”

Two‐Dimensional Metal Telluride Atomic Crystals: Preparation, Physical Properties, and Applications

“…Wang et al. [ 76 ] reported the epitaxial growth of Cr 2 Te 3 thin film with a NiAs‐type hexagonal structure on the Al 2 O 3 substrate. As illustrated in Figure a, high‐purity Te and Cr powers are respectively evaporated by two Knudsen cells for offering individual fluxes, and co‐deposited on the pretreated Al 2 O 3 substrates at 370 °C.…”

“…Reproduced with permission. [ 76 ] Copyright 2019, American Chemical Society. d) Schematic of the MBE growth setup; e) the process control and substrate temperature profile of the growth of MoTe 2 by MBE; I: heating, II: growth/nucleation, III: annealing, IV: cooling.…”

“…Wang et al. [ 76 ] discovered that the T C of Cr 2 Te 3 thin film grown by epitaxy can be adjusted by doping of Al, which offers a new approach for the preparation of 2D MTACs‐based spintronic devices operating under near‐environmental conditions.…”