A hexagon based Mn(ii) rod metal-organic framework - structure, SF6 gas sorption, magnetism and electrochemistry

A manganese(ii) metal-organic framework based on the hexatopic hexakis(4-carboxyphenyl)benzene, cpb6−: [Mn3(cpb)(dmf)3], was solvothermally prepared showing a Langmuir area of 438 m2 g−1, rapid uptake of sulfur hexafluoride (SF6) as well as electrochemical and magnetic properties, while single crystal diffraction reveals an unusual rod-MOF topology

Strong in-plane magnetic anisotropy (Co0.15Fe0.85)5GeTe2/graphene van der Waals heterostructure spin-valve at room temperature

Van der Waals (vdW) magnets are promising owing to their tunable magnetic properties with doping or alloy composition, where the strength of magnetic interactions, their symmetry, and magnetic anisotropy can be tuned according to the desired application. However, most of the vdW magnet based spintronic devices are so far limited to cryogenic temperatures with magnetic anisotropies favouring out-of-plane or canted orientation of the magnetization. Here, we report room-temperature lateral spin-valve devices with strong in-plane magnetic anisotropy of the vdW ferromagnet (Co0.15Fe0.85)5GeTe2 (CFGT) in heterostructures with graphene. Magnetization measurements reveal above room-temperature ferromagnetism in CFGT with a strong in-plane magnetic anisotropy. Density functional theory calculations show that the magnitude of the anisotropy depends on the Co concentration and is caused by the substitution of Co in the outermost Fe layer. Heterostructures consisting of CFGT nanolayers and graphene were used to experimentally realize basic building blocks for spin valve devices such as efficient spin injection and detection. The spin transport and Hanle spin precession measurements prove a strong in-plane and negative spin polarization at the interface with graphene, which is supported by the calculated spin-polarized density of states of CFGT. The in-plane magnetization of CFGT at room temperature proves its usefulness in graphene lateral spin-valve devices, thus opening further opportunities for spintronic technologies

A Room-Temperature Spin-Valve with van der Waals Ferromagnet Fe5GeTe2/Graphene Heterostructure

The discovery of van der Waals (vdW) magnets opened a new paradigm for condensed matter physics and spintronic technologies. However, the operations of active spintronic devices with vdW ferromagnets are limited to cryogenic temperatures, inhibiting their broader practical applications. Here, the robust room-temperature operation of lateral spin-valve devices using the vdW itinerant ferromagnet Fe5GeTe2 in heterostructures with graphene is demonstrated. The room-temperature spintronic properties of Fe5GeTe2 are measured at the interface with graphene with a negative spin polarization. Lateral spin-valve and spin-precession measurements provide unique insights by probing the Fe5GeTe2/graphene interface spintronic properties via spin-dynamics measurements, revealing multidirectional spin polarization. Density functional theory calculations in conjunction with Monte Carlo simulations reveal significantly canted Fe magnetic moments in Fe5GeTe2 along with the presence of negative spin polarization at the Fe5GeTe2/graphene interface. These findings open opportunities for vdW interface design and applications of vdW-magnet-based spintronic devices at ambient temperatures

Structural, vibrational, elastic, electronic, and piezoelectric properties of binary gamma-GeX and ternary gamma-Ge2XX' monolayers (X, X'= S, Se, and Te)

The recent synthesis of a new polymorph of two-dimensional (2D) germanium monochalcogenides, namely, gamma -GeSe with a four-atomic-layer-thick hexagonal lattice, has received considerable attention due to its novel properties and potential applications. This exciting advancement paves the path for extensive experimental and theoretical investigations on the family of gamma -MX crystals in which M and X are elements of group IV and VI, respectively. In this regard, herein we conduct first-principles-based calculations to explore the structural, vibrational, mechanical, electronic, and piezoelectric properties of gamma -GeX and Janus gamma -Ge2XX' (X/X' : S, Se, and Te) monolayers. We performed a detailed analysis of the suggested systems' dynamical, thermal, and mechanical stability through phonon-band-dispersion calculations, ab initio molecular dynamics (AIMD) simulations, and elastic tensor analyses, respectively, and all six possible nanosheets are found to be stable. The computed Raman spectra of the monolayers reveal that, different from binary systems, the formation of Janus monolayers results in the appearance of additional Raman active modes. The mechanical response of the proposed crystals is examined by calculating in-plane stiffness (Y2D) and the Poisson's ratio (nu) within the elastic regime, and the obtained results ascertain their flexibility. It is found that similar to their binary counterparts, Janus monolayers are indirect-band-gap semiconductors, and their valence-band maxima show a Mexican hat dispersion along the high-symmetry points of the Brillouin zone. Additionally, it is demonstrated that the construction of Janus crystals enhances the piezoelectric coefficients of gamma -GeX monolayers, both in the in-plane and out-of-plane directions. Our findings not only provide a comprehensive insight into physical and electronic properties of gamma -GeX and gamma -Ge2XX' monolayers but also reveal their promising features for various nanoelectronic and nanoelectrochemical applications

Unraveling effects of electron correlation in two-dimensional Fe n GeTe2 (n = 3, 4, 5) by dynamical mean field theory

Abstract The Fe n GeTe2 systems are recently discovered two-dimensional van-der-Waals materials, exhibiting magnetism at room temperature. The sub-systems belonging to Fe n GeTe2 class are special because they show site-dependent magnetic behavior. We focus on the critical evaluation of magnetic properties and electron correlation effects in Fe n GeTe2 (n = 3, 4, 5) (FGT) systems performing first-principles calculations. Three different ab initio approaches have been used primarily, viz., (i) standard density functional theory (GGA), (ii) incorporating static electron correlation (GGA + U) and (iii) inclusion of dynamic electron correlation effect (GGA + DMFT). Our results show that GGA + DMFT is the more accurate technique to correctly reproduce the magnetic interactions, experimentally observed transition temperatures and electronic properties. The inaccurate values of magnetic moments, exchange interactions obtained from GGA + U make this method inapplicable for the FGT family. Correct determination of magnetic properties for this class of materials is important since they are promising candidates for spin transport and spintronic applications at room temperature

Unusual Magnetic Features in Two-Dimensional Fe5GeTe2 Induced by Structural Reconstructions

Recent experiments on Fe5GeTe2 suggested the presence of a symmetry breaking of its conventional crystal structure. Here, using density functional theory calculations, we elucidate that the stabilization of the (root 3 X root 3)R30 degrees supercell structure is caused by the swapping of Fe atoms occurring in the monolayer limit. The swapping to the vicinity of Te atoms is facilitated by the spontaneous occurrence of Fe vacancy and its low diffusion barrier. Our calculated magnetic exchange parameters show the simultaneous presence of ferromagnetic and antiferromagnetic exchange among a particular type of Fe atom. The Fe sublattice projected magnetization obtained from Monte Carlo simulations dearly demonstrates an exotic temperature-dependent behavior of this Fe type along with a large canting angle at T = 0 K, indicating the presence of a complex noncollinear magnetic order. We propose that the low-temperature crystal structure results from the swapping between two sublattices of Fe, giving rise to peculiar magnetization obtained in experiments