Colossal Anomalous Hall Effect in Ferromagnetic van der Waals CrTe₂

Abstract

van der Waals crystals exhibit excellent material performance when exfoliated to few-atomic-layer thickness. In contrast, the van der Waals thin films more than 10 nm thick are believed to show bulk properties, in which outstanding material performance is rarely found. Here we report the largest anomalous Hall conductivity observed so far in a 170 nm van der Waals ferromagnetic 1T-CrTe2 flake, which reaches 67,000 Ω–1 cm–1. Such a colossal anomalous Hall conductivity in 1T-CrTe2 is dominated by the extrinsic skew scattering process rather than the intrinsic Berry phase effect, as evidenced by the linear relation between the anomalous Hall conductivity and the longitudinal conductivity. Defying the dilemma of mutually exclusive large anomalous Hall angle and high electric conductivity for most ferromagnets, 1T-CrTe2 achieves both in a thin film sample. Considering the shared physics of the anomalous Hall effect and the spin Hall effect, our finding offers a guideline for searching large spin Hall materials of high conductivity which may overcome the bottleneck of overheating in spintronics devices.

Above-room-temperature strong intrinsic ferromagnetism in 2D van der Waals Fe3GaTe2 with large perpendicular magnetic anisotropy

“…Notably, the θ AH persists 3% at room temperature. Such large room temperature θ AH is comparable to θ AH of other classical ferromagnetic materials such as Fe and (Ga, Mn)As, and much larger than that of other vdW ferromagnetic crystals 9,26,27 (Supplementary Table 6).…”

“…However, up to now, robust large room-temperature PMA only exists in conventional non-vdW ferromagnetic thin films like CoFeB (magnetic anisotropy energy density K u , 2.1 × 10 5 J/m 3 ) 1 . No intrinsic 2D vdW ferromagnetic crystals such as CrI 3 , Cr 2 Ge 2 Te 6 , Fe 3 GeTe 2 and CrTe 2 combine above-room-temperature intrinsic strong ferromagnetism (e.g., saturation magnetic moment M sat only ~12.5 emu/g in CrTe 2 at 300 K 9 ) and robust large room-temperature PMA (e.g., K u only 4.9 × 10 4 J/m 3 in 2D CrTe 2 thin film at 300 K 10 , one order of magnitude lower than widely-used CoFeB thin film) 8,[11][12][13][14][15] . 2D vdW intrinsic ferromagnetic crystals with above-room-temperature Curie temperature (T C ) and robust large room-temperature PMA are still elusive, but fundamentally important for room-temperature electrically control ferromagnetism and next-generation, roomtemperature-operated 2D low-power magnetoelectronic and spintronic devices.…”

Van der Waals Superstructure and Twisting in Self-Intercalated Magnet with Near Room-Temperature Perpendicular Ferromagnetism

“…While many efforts have been focused on studying transition metal trihalides (e.g., CrI 3 ), ,,− they have often been shown to be unstable and degrade within minutes in air and/or when exposed to light, requiring either in situ measurements in an oxygen-free environment or encapsulation between protective layers to prevent deterioration. , Conversely, transition metal telluride compounds are expected to be relatively more stable in ambient conditions. Among various vdW magnetic tellurides, the binary chromium telluride 1T-CrTe 2 has a ferromagnetic ordering temperature T c above room temperature, − which is significantly higher than that of the previously studied ternary chromium tellurides Cr 2 X 2 Te 6 (X = Si, Ge). ,,− Furthermore, a colossal anomalous Hall conductivity was recently observed in 1T-CrTe 2 with simultaneously large anomalous Hall angles and electrical conductivities distinct from other anomalous Hall materials, making it an excellent candidate for spintronics applications. , By intercalating Cr atoms into the vdW gap between the CrTe 2 layers, as shown in Figure a, different chromium telluride compounds Cr 1+δ Te 2 (0 < δ ≤ 1) are created. These different Cr 1+δ Te 2 phases have a broad range of magnetic ordering temperatures and novel magnetic phases. ,,,− For example, CrTe (or Cr 2 Te 2 ) thin films have been reported to exhibit the topological Hall effect, noted as strong evidence of a magnetic skyrmion phase .…”

“…1,14,37−44 Furthermore, a colossal anomalous Hall conductivity was recently observed in 1T-CrTe 2 with simultaneously large anomalous Hall angles and electrical conductivities distinct from other anomalous Hall materials, making it an excellent candidate for spintronics applications. 33,45 By intercalating Cr atoms into the vdW gap between the CrTe 2 layers, as shown in Figure 1a, different chromium telluride compounds Cr 1+δ Te 2 (0 < δ ≤ 1) are created. These different Cr 1+δ Te 2 phases have a broad range of magnetic ordering temperatures and novel magnetic phases.…”

Observation of Exchange Bias in Antiferromagnetic Cr0.79Se Due to the Coexistence of Itinerant Weak Ferromagnetism at Low Temperatures

“…However, FeTe is always a tetragonal antiferromagnetic system with a stripe order. , Further, FeS is found to be a nonmagnetic superconductor with a tetragonal crystal structure . On the other hand, similar to Fe x X, Cr x X (X = S, Se, Te) systems too are diverse in their structural, electronic, and magnetic properties. − For instance, Cr x Te is a ferromagnetic half-metal and can exist in any zinc blend (ZB), rock salt (RS), or NiAs crystal structure type, whereas Cr x S and Cr x Se are mostly known for their antiferromagnetic nature with the NiAs-type crystal structure. Some reports suggested Cr x Se to be a spin-glass-type magnetic system and Cr x S to be a ferrimagnetic metal …”