Structure and Magnetism of Iron- and Chromium-Intercalated Niobium and Tantalum Disulfides

Abstract

Transition metal dichalcogenides (TMDs) intercalated with spin-bearing transition metal centers are a diverse class of magnetic materials where the spin density and ordering behavior can be varied by the choice of host lattice, intercalant identity, level of intercalation, and intercalant disorder. Each of these degrees of freedom alters the interplay between several key magnetic interactions to produce disparate collective electronic and magnetic phases. The array of magnetic and electronic behavior typified by these systems renders them distinctive platforms for realizing tunable magnetism in solid-state materials and promising candidates for spin-based electronic devices. This Perspective provides an overview of the rich magnetism displayed by transition metal-intercalated TMDs by considering Fe- and Cr-intercalated NbS2 and TaS2. These four exemplars of this large family of materials exhibit a wide range of magnetic properties, including sharp switching of magnetic states, current-driven magnetic switching, and chiral spin textures. An understanding of the fundamental origins of the resultant magnetic/electronic phases in these materials is discussed in the context of composition, bonding, electronic structure, and magnetic anisotropy in each case study.

Bridging Structure, Magnetism, and Disorder in Iron-Intercalated Niobium Diselenide, FexNbSe2, below x = 0.25

“…25 The frequency range of these features appears consistent with phonon modes attributed to intercalant superlattice formation in other T x MCh 2 compounds. 2,13,25 Additionally, the sharp linewidths for the superlattice features in the x = 0.23 sample are consistent with a clear 2a 0 × 2a 0 intercalant superstructure in the Fe 0.23 NbSe 2 crystal structure. The intermediate but incomplete growth of superlattice Raman peaks for x = 0.19 crystal, on the other hand, suggests the formation of a defective superlattice with missing intercalants, compared to x = 0.23, which would also be in conjunction with a clear but weaker AFM transition for x = 0.19 in the magnetic susceptibility data (Figure 2a).…”

“…In Raman scattering, three intercalant superlattice modes emerge at 97, 113, and 125 cm –1 at x = 0.19 and become more intense and well resolved as Fe concentration increases to x = 0.23. Future studies will aim to map out the Raman-active modes for higher intercalation amounts in the Fe x NbSe 2 family, namely, for 0.25 ≤ x ≤ 0.33 and for x > 0.33, in which a crossover to a noncentrosymmetric P 6 3 22 space group is expected and thus a √3 a 0 × √3 a 0 superlattice should be observed. ,,, Assessing the extent of magnetoelastic coupling in the intercalation regime near x = 0.33 would also lend valuable insight as to whether fundamentally new phonons can emerge from zone-folding and couple directly with the spin ordering in the system. Furthermore, examining how the modes for a different superlattice prevail within Fe x NbSe 2 will play a key role in screening for different superlattice formation within a given crystal, providing a road map for probing and exploiting local disorder and coexisting structural domains within this magnetically intercalated TMD family.…”

Hard Ferromagnetism Down to the Thinnest Limit of Iron-Intercalated Tantalum Disulfide

“…Transition metal dichalcogenides (TMDs) intercalated with open-shell transition metals comprise a family of materials with inherently tunable MCA, which makes them appealing targets for realizing 2D magnets with deterministic properties. The strength of MCA in intercalated TMDs is determined by the respective magnitudes of spin–orbit coupling (SOC) and unquenched orbital angular momentum (OAM) of the spin-bearing ions. − While the SOC is increased when the host lattice or the intercalants comprise heavy elements, the OAM of spin-bearing ions is shaped by their oxidation states and coordination environments imposed by the interlayer galleries. − However, low-dimensional analogues of these systems have not been magnetically characterized; strong interlayer interactions in the effectively ionic, bulk crystals of these intercalation compounds have, so far, precluded exfoliation of pristine, large 2D flakes suited for magnetic studies. − Consequently, the manifold possibilities for designing a new class of 2D magnets with controllable MCA by exploiting the tunable vdW interface, host lattice, and intercalant identity/stoichiometry remain untapped.…”

An emergence of chiral helimagnetism or ferromagnetism governed by Cr intercalation in a dichalcogenide CrNb3S6

“…In order to discuss the dome-shaped behavior of T c in detail, additional experiments will be necessary. A similar behavior is exhibited by another transition metal sulfides such as ferromagnetic Fe-intercalated tantalum sulfide, and is discussed from the viewpoint of oscillatory characteristics of Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction 45 . The Cr-Cr distance determined by single crystal X-ray diffraction measurements and the carrier concentration by Hall measurements will be helpful for understanding the mechanism of the domeshaped behavior.…”