Tunable Room-Temperature Ferromagnetism in Two-Dimensional Cr₂Te₃

Abstract

The manipulation of magnetism provides a unique opportunity for the development of data storage and spintronic applications. Until now, electrical control, pressure tuning, stacking structure dependence, and nanoscale engineering have been realized. However, as the dimensions are decreased, the decrease of the ferromagnetism phase transition temperature (T c) is a universal trend in ferromagnets. Here, we make a breakthrough to realize the synthesis of 1 and 2 unit cell (UC) Cr2Te3 and discover a room-temperature ferromagnetism in two-dimensional Cr2Te3. The newly observed T c increases strongly from 160 K in the thick flake (40.3 nm) to 280 K in 6 UC Cr2Te3 (7.1 nm). The magnetization and anomalous Hall effect measurements provided unambiguous evidence for the existence of spontaneous magnetization at room temperature. The theoretical model revealed that the reconstruction of Cr2Te3 could result in anomalous thickness-dependent T c. This dimension tuning method opens up a new avenue for manipulation of ferromagnetism.

Highly Tunable Near‐Room Temperature Ferromagnetism in Cr‐Doped Layered Td‐WTe2

“…The corresponding elemental characterizations are shown in Table S1, Supporting Information). For the Cr precursor atomic ratio of C3, the obtained product contained two completely separated different single crystals: Cr‐doped layered Td‐WTe 2 (namely C3Cr‐WTe 2 ‐needle) and non‐van der Waals Cr 2 Te 3 [ 29 ] (Figure S2, Supporting Information). Moreover, the collected Cr 2 Te 3 single crystals were flake‐like with a gray surface and they could not be exfoliated with Scotch tape (Figure S1d, Supporting Information).…”

“…[ 31 ] The W cations in the Td–WTe 2 are arranged in zigzag metal–metal chains and the Te anions were arranged asymmetrically around the W cations, [ 30 ] whereas the Cr cations tended to form linear metal–metal chains in the Cr–Te system instead of the zigzag chains. [ 29 ] Hence, we assumed that the microstructure of the Cr‐doped WTe 2 would become “straighter” with a slightly larger lattice constant compared with the pure WTe 2 . To further identify the location of the Cr dopants within the WTe 2 lattice, the atomic‐resolution images for the Cr 0.01 –WTe 2 and Cr 0.02 –WTe 2 samples were extracted from their HRTEM images, as shown in Figure S10 (Supporting Information).…”

“…Recently, Yao et al. reported that chemical vapor deposition (CVD)‐grown few‐layer Cr 2 Te 3 exhibited two Curie temperatures ( T c ), [ 29 ] which were greatly influenced by the ratio of the elemental Cr and Te. Additionally, an early study also indicated that both the T c and the ferromagnetic moment of a Cr–Te system would decrease gradually with the increase of the Te content, and they were highly affected by Cr valence states.…”

“…Therefore, the current results were reasonable and quite consistent with the previously reported ferromagnetic properties and T c modulation interpretation of a Cr–Te material system. [ 29,35 ] Moreover, we also performed density functional theory (DFT) theoretical calculation for the WTe 2 with two Cr doping concentrations (Cr 0.03 W 0.97 Te 2 and Cr 0.06 W 0.94 Te 2 ), as shown in Figure S12 in the Supporting Information. The partial density of states (DOSs) of the W‐5d and Te‐5p of the Cr 0.03 W 0.97 Te 2 and the Cr 0.06 W 0.94 Te 2 were essentially symmetrical (Figure S12e,f, Supporting Information), while the partial DOS of the Cr‐3d exhibited great asymmetry (Figure S12g,h, Supporting Information), which could cause spin polarization to induce magnetism in the WTe 2 .…”

“…Figure 3d also shows the zero-field cooling (ZFC) and field cooling (FC) M-T curves of the Cr 0.01 -WTe 2 , in which two Curie transition points at 197 and 283 K can be clearly observed, which could be further confirmed from its spontaneous magnetization curve (Figure 3e). Recently, Yao et al reported that chemical vapor deposition (CVD)-grown few-layer Cr 2 Te 3 exhibited two Curie temperatures (T c ), [29] which were greatly influenced by the ratio of the elemental Cr and Te. Additionally, an early study also indicated that both the T c and the ferromagnetic moment of a Cr-Te system would decrease gradually with the increase of the Te content, and they were highly affected by Cr valence states.…”