Transport properties, magnetic susceptibility and Mössbauer spectroscopy of Fe0.25NbS2 and Fe0.33NbS2

Fe Site Order and Magnetic Properties of Fe1/4NbS2

Transition-metal dichalcogenides (TMDs) have long been attractive to researchers for their diverse properties and high degree of tunability. Most recently, interest in magnetically intercalated TMDs has resurged due to their potential applications in spintronic devices. While certain compositions featuring the absence of inversion symmetry such as Fe1/3NbS2 and Cr1/3NbS2 have garnered the most attention, the diverse compositional space afforded through the host matrix composition as well as intercalant identity and concentration is large and remains relatively underexplored. Here, we report the magnetic ground state of Fe1/4NbS2 that was determined from low-temperature neutron powder diffraction as an A-type antiferromagnet. Despite the presence of overall inversion symmetry, the pristine compound manifests spin polarization induced by the antiferromagnetic order at generic k points, based on density functional theory band-structure calculations. Furthermore, by combining synchrotron diffraction, pair distribution function, and magnetic susceptibility measurements, we find that the magnetic properties of Fe1/4NbS2 are sensitive to the Fe site order, which can be tuned via electrochemical lithiation and thermal history.

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

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.

Cd additive effect on self-flux growth of Cs-intercalated NbS2 superconducting single crystals

Single crystals of Cs-intercalated NbS2 (Cs x NbS2) were synthesized using a CsCl/KCl self-flux. The size and Cs content of Cs x NbS2 single crystals increased upon adding Cd metal into the starting materials. When 10–30 at% of Cd per Nb was provided in the starting materials, plate-like Cs x NbS2 (x ∼ 0.3) single crystals with 1–2 mm in size and 10–100 μm in thickness were obtained. The superconducting transition temperature of these Cs x NbS2 single crystals was 1.65 K.

Pressure-Driven Sequential Lattice Collapse and Magnetic Collapse in Transition-Metal-Intercalated Compounds FexNbS2

Volume collapse under high pressure is an intriguing phenomenon involving subtle interplay between lattice, spin, and charge. The two most important causes of volume collapse are lattice collapse (low-density to high-density) and magnetic collapse (high-spin to low-spin). Herein we report the pressure-driven sequential volume collapses in partially intercalated Fe_xNbS₂ (x = 1/4, 1/3, 1/2, 2/3). Because of the distinct interlayer atomic occupancy, the low-iron-content samples exhibit both lattice and magnetic collapses under compression, whereas the high-iron-content samples exhibit only one magnetic collapse. Theoretical calculations indicate that the low-pressure volume collapses for x = 1/4 and x = 1/3 are lattice collapses, and the high-pressure volume collapses for all four samples are magnetic collapses. The magnetic collapse involving the high-spin to low-spin crossover of Fe²⁺ has also been verified by in situ X-ray emission measurements. Integrating two distinct volume collapses into one material provides a rare playground of lattice, spin, and charge.

Three-state nematicity in the triangular lattice antiferromagnet Fe1/3NbS2

Nematic order is the breaking of rotational symmetry in the presence of translational invariance. While originally defined in the context of liquid crystals, the concept of nematic order has arisen in crystalline matter with discrete rotational symmetry, most prominently in the tetragonal Fe-based superconductors where the parent state is four-fold symmetric. In this case the nematic director takes on only two directions, and the order parameter in such 'Ising-nematic' systems is a simple scalar. Here, using a spatially resolved optical polarimetry technique, we show that a qualitatively distinct nematic state arises in the triangular lattice antiferromagnet Fe_1/3NbS₂. The crucial difference is that the nematic order on the triangular lattice is a [Formula: see text] or three-state Potts-nematic order parameter. As a consequence, the anisotropy axes of response functions such as the resistivity tensor can be continuously reoriented by external perturbations. This discovery lays the groundwork for devices that exploit analogies with nematic liquid crystals.

Electrical switching in a magnetically intercalated transition metal dichalcogenide

Advances in controlling the correlated behaviour of transition metal dichalcogenides have opened a new frontier of many-body physics in two dimensions. A field where these materials have yet to make a deep impact is antiferromagnetic spintronics-a relatively new research direction promising technologies with fast switching times, insensitivity to magnetic perturbations and reduced cross-talk^1-3. Here, we present measurements on the intercalated transition metal dichalcogenide Fe_1/3NbS₂ that exhibits antiferromagnetic ordering below 42 K (refs. ^4,5). We find that remarkably low current densities of the order of 10⁴ A cm^-2 can reorient the magnetic order, which can be detected through changes in the sample resistance, demonstrating its use as an electronically accessible antiferromagnetic switch. Fe_1/3NbS₂ is part of a larger family of magnetically intercalated transition metal dichalcogenides, some of which may exhibit switching at room temperature, forming a platform from which to build tuneable antiferromagnetic spintronic devices^6,7.

Electronic and magnetic properties of the 2H-NbS2 intercalated by 3d transition metal atoms

The electronic structure and magnetic properties of the compound 2H-NbS2 intercalated by 3d elements from Cr to Ni, have been investigated using the Korringa–Kohn–Rostoker electronic structure method. Here, we consider the phases with 33% of intercalation within the ordered phase having a 3 × 3 $\sqrt 3 \times \sqrt 3 $ arrangement of the magnetic atoms. We analyze the relationship of the magnetic and electronic properties on the structural parameters dependent on the intercalant. The exchange coupling parameters calculated from first principles have been used for subsequent Monte Carlo simulations. Within these investigations, the FM order was found for the Cr and Mn intercalated phases as ground state configuration with a Curie temperature being in good agreement with the experiment. According to the Monte Carlo simulation, Fe1/3NbS2 has a complicated noncollinear magnetic structure with a noncompensated total magnetic moment, whereas Co1/3NbS2 and Ni1/3NbS2 are found to be antiferromagnetic, all in line with experimental observations.