Escalating Ferromagnetic Order via Se‐Vacancies Near Vanadium in WSe₂ Monolayers

Abstract

as core materials for future spintronics given their potential for high Curie temperature (T C ) and efficient field-tunable magnetic properties. [1][2][3] Despite half-century-long research efforts, the following three primary issues remain unsolved: i) the uncertain origin of ferromagnetism, called phantom ferromagnetism, owing to a lack of structural analysis of nanodefects; [4,5] ii) solubility limit to only a few percent without forming aggregation; [6] and iii) activation of short-range antiferromagnetic transitions in the high-dopingconcentration regime, [7] which limits the improvement of the magnetic moment and T C .The recent emergence of magnetic order in 2D van der Waals layered materials, which is enabled by strong magnetic anisotropy, [8] has stimulated interest in 2D-DMSs owing to their exotic spindependent physical properties, including long spin-relaxation time, light-controlled magnetism, [9] and spin-valley locking, inherent to their atomically thin nature. [10][11][12] In particular, transition metal dichalcogenide (TMD) semiconductors with magnetic dopants synthesized via chemical vapor deposition (CVD) offer room-temperature T C and gate-tunable magnetism. [13][14][15] Although vanadium dopants in WSe 2 and WS 2 semiconductors have been successfully distributed randomly without aggregation to a relatively high doping concentration of approximately 10%, their saturation magnetization is still limited to approximately 10 −5 emu cm −2 , thus making further analysis and applications difficult. [14,15] While magnetism has been proposed for inducing various defects such as vacancies, [16] anti-sites, [17] and grain boundaries [18] in III-V, oxides, and nitride DMSs, the underlying mechanism of magnetism is little known mainly due to the lack of structural analysis. On the contrary, because of facile monolayer growth, a variety of defects, including transition metal and chalcogen vacancies in 2D-TMDs, can be precisely analyzed using state-of-the-art scanning transmission electron microscopy (STEM) with atomic elemental mapping. [19] This affords the possibility of elucidating the origins of magnetism from defects and further enhancing magnetic order by tailoring intrinsic defects and impurities in 2D-TMD semiconductors. Here, we present a comprehensive atomic analysis of Se-vacancy defects Magnetic order has been proposed to arise from a variety of defects, including vacancies, antisites, and grain boundaries, which are relevant in numerous electronics and spintronics applications. Nevertheless, its magnetism remains controversial due to the lack of structural analysis. The escalation of ferromagnetism in vanadium-doped WSe 2 monolayer is herein demonstrated by tailoring complex configurations of Se vacancies (Se Vac ) via post heat-treatment. Structural analysis of atomic defects is systematically performed using transmission electron microscopy (TEM), enabled by the monolayer nature. Temperature-dependent magnetoresistance hysteresis ensures enhanced magnetic order after high-temperature heat-tre...

Two-dimensional multiferroic material of metallic p-doped SnSe

“…Interestingly, the phase deviation between p-doped SnSe and nonmagnetic SiO 2 /Si substrate is obviously observed, indicating its ferromagnetic order (Supplementary Fig. S21 ), the similar phenomena are also demonstrated in monolayer V-doped WSe 2 35 and monolayer VSe 2 36 . Notably, the single magnetic domain is obtained for p-doped SnSe, which is similar to 2D ferromagnetism Fe 3 GaTe 2 37 .…”

Enhanced Magnetism in Heterostructures with Transition-Metal Dichalcogenide Monolayers

“…The total DOS increase at the Fermi level, larger magnetization, and importantly much enhanced spin density at the interface with overlapping majority and minority regions in the FS of Fe/WSe 2 /Pt HST influence the electronic and spin transport across the interface. The combined effect of all of these factors results in larger spin Seebeck coefficients in HSTs with TMDC layers, which can be useful in interpreting recent experiments reporting enhanced magnetization and spin-resolved transport properties. − ,− ,,, …”

“…Specifically, a large enhancement of the voltage difference due to the longitudinal spin Seebeck effect in Pt/Ni 81 Fe 19 and Pt/YIG after inserting WS 2 (WSe 2 ) layers has been reported. − It was also found that such an increase is dependent on the number of layers in the heterostructure, degree of coverage by the TMDC layers, and quality of the interface. Others have examined spin-dependent transport in Fe 3 O 4 /MoS 2 /Fe 3 O 4 and Co/Al 2 O 3 /MoS 2 junctions. , Spin valves based on spin filtering in WS 2 /Co and NiFe/MoS 2 /NiFe have also been reported. , A gate-tunable magnetic order in WSe 2 by changing the occupation of the Se vacancy states is successfully demonstrated, and computational work investigates the origin of ferromagnetism in complex configurations of Se vacancies in V-doped WSe 2 monolayers . The generated Se vacancies play a key role in the structural change of PdSe 2 because of the laser-induced phase transformation of layered PdSe 2 to metallic phase PdSe 2– x .…”

“…18,19 A gate-tunable magnetic order in WSe 2 by changing the occupation of the Se vacancy states is successfully demonstrated, 20 and computational work investigates the origin of ferromagnetism in complex configurations of Se vacancies in V-doped WSe 2 monolayers. 21 The generated Se vacancies play a key role in the structural change of PdSe 2 because of the laser-induced phase transformation of layered PdSe 2 to metallic phase PdSe 2−x . 22 Ozyilmaz et al suggested that the spin Hall effect in graphene/TMDC heterostructures may also originate from chalcogenide vacancies.…”

“…The combined effect of all of these factors results in larger spin Seebeck coefficients in HSTs with TMDC layers, which can be useful in interpreting recent experiments reporting enhanced magnetization and spin-resolved transport properties. [5][6][7][12][13][14][15]18,20,21 ■ COMPUTATIONAL METHODS The first-principles simulations are performed with the DFT Vienna ab initio simulations package (VASP), which is based on projector-augmented wave (PAW) pseudopotentials and periodic boundary conditions. 34,35 The exchange-correlation effects are considered using the Perdew−Burke−Ernzerhof (PBE) generalized gradient approximation with included spin−orbit coupling (SOC).…”