5 research outputs found
Ultrahigh breakdown current density of van der Waals One Dimensional
One-dimensional (1D) van der Waals (vdW) materials offer nearly defect-free
strands as channel material in the field-effect transistor (FET) devices and
probably, a better interconnect than conventional copper with higher current
density and resistance to electro-migration with sustainable down-scaling. We
report a new halide based "truly" 1D few-chain atomic thread, PdBr,
isolable from its bulk which crystallizes in a monoclinic space group C2/c.
Liquid phase exfoliated nanowires with mean length (201)m transferred
onto SiO/Si wafer with a maximum aspect ratio of 5000 confirms the lower
cleavage energy perpendicular to chain direction. Moreover, an isolated
nanowire can also sustain current density of 200 MA/cm which is
atleast one-order higher than typical copper interconnects. However, local
transport measurement via conducting atomic force microscopy (CAFM) tip along
the cross direction of the single chain records a much lower current density
due to the anisotropic electronic band structure. While 1D nature of the
nanoobject can be linked with non-trivial collective quantum behavior, vdW
nature could be beneficial for the new pathways in interconnect fabrication
strategy with better control of placement in an integrated circuit (IC)
Spin-crossover assisted metallization of few-layer FePS at 1.45 GPa
Magnetic insulators in reduced dimension are the ideal model systems to study
spin-crossover(SCO) induced cooperative behavior under pressure. Similar to the
external perturbations like light illumination or temperature, external
pressure may provide new pathway to accelerate giant lattice collapse,and
subsequently Mott transition in van der Waals (vdW) materials with diminishing
effect of the third dimension. Here, we investigate room-temperature
layer-dependent SCO and insulator-metal transition in vdW magnet,FePS3, under
high pressure using micro-Raman scattering.Experimentally obtained spectra, in
agreement with the computed Raman modes, indicates evidence of IMT of FePS3
started off with a spin-state transition from a high (S=2) to low spin state
(S=0) with a thickness dependent critical pressure (P_c) which reduces to 1.45
GPa in 3-layer flakes compared to 10.8 GPa for the bulk counterpart.
Additionally, a broad Raman mode (P*) emerges between 310 cm^{-1} and 370
cm^{-1} at elevated pressure for three different thicknesses of FePS3 flakes
(3-100 layers), also corroborated with computational results which suggests the
pressure dependent decrease of metal-ligand bond distance(Fe-S) with lowering
of magnetic moment in FePS3. Phenomenologically, our results in few-layer
flakes with strong structural anisotropy which enhances the in-plane strain
with applied pressure can be understood by adopting Hubbard model and
considering the spectral-range (bandwidth W) as a function of layer numbers and
pressure with a power-law scaling. Reduction of the critical pressure for phase
transition in few-layer vdW magnets to 1-2 GPa marks the possibility of using
nano-enclosure fit for use in device electronics where the pressure is induced
due to interfacial adhesion, like in vdW heterostructure or molecules trapped
between layers,and thereby,avoiding the conventional use of diamond anvil cell
Proximitized spin-phonon coupling in topological insulator due to two-dimensional antiferromagnet
Induced magnetic order in a topological insulator (TI) can be realized either
by depositing magnetic adatoms on the surface of a TI or engineering the
interface with epitaxial thin film or stacked assembly of two-dimensional (2D)
van der Waals (vdW) materials. Herein, we report the observation of spin-phonon
coupling in the otherwise non-magnetic TI BiTe, due
to the proximity of FePS (an antiferromagnet (AFM),
120 K), in a vdW heterostructure framework. Temperature-dependent Raman
spectroscopic studies reveal deviation from the usual phonon anharmonicity
at/below 60 K in the peak position (self-energy) and linewidth (lifetime) of
the characteristic phonon modes of BiTe (106 cm and 138
cm) in the stacked heterostructure. The Ginzburg-Landau (GL) formalism,
where the respective phonon frequencies of BiTe couple to phonons
of similar frequencies of FePS in the AFM phase, has been adopted to
understand the origin of the hybrid magneto-elastic modes. At the same time,
the reduction of characteristic of FePS from 120 K in
isolated flakes to 65 K in the heterostructure, possibly due to the interfacial
strain, which leads to smaller Fe-S-Fe bond angles as corroborated by
computational studies using density functional theory (DFT). Besides, our data
suggest a double softening of phonon modes of BiTe
(at 30 K and 60 K), which in turn, demonstrates Raman scattering as a possible
probe for delineating the magnetic ordering in bulk and surface of a hybrid
topological insulator
Anisotropic magnetodielectric coupling in layered antiferromagnetic FePS 3
We report anisotropic magnetodielectric coupling in layered van der Waals antiferromagnetic FePS3 (Néel temperature TN∼ 120 K) with perpendicular anisotropy. Above TN, while the dielectric response function along the c axis shows frequency-dependent relaxations, in-plane data is frequency independent and reveals a deviation from phonon-anharmonicity in the ordered state, thereby implying a connection to spin-phonon coupling known to be indicative of onset of magnetic ordering. At low temperature (below 40 K), atypical anomaly in the dielectric constant is corroborated with temperature-dependent dc and ac susceptibility. The magnetodielectric response across this anomaly differs significantly for both in-plane and out-of-plane cases. We have explained this in terms of preferential orientation of magnetic antiferromagnetic zigzag alignment, implied by the in-plane structural anisotropy as confirmed by ab initio calculations. Controlling the relative strength of magnetodielectric coupling with magnetic anisotropy opens a strategy for tracking subtle modifications of structures, such as in-plane anisotropy, with potential applications for spintronic technologies
Emergence of a Non-van der Waals Magnetic Phase in a van der Waals Ferromagnet
International audienceManipulation of long-range order in two-dimensional (2D) van der Waals (vdW) magnetic materials (e.g., CrI, CrSiTe etc.), exfoliated in few-atomic layer, can be achieved via application of electric field, mechanical-constraint, interface engineering, or even by chemical substitution/doping. Usually, active surface oxidation due to the exposure in the ambient condition and hydrolysis in the presence of water/moisture causes degradation in magnetic nanosheets which, in turn, affects the nanoelectronic/spintronic device performance. Counterintuitively, our current study reveals that exposure to the air at ambient atmosphere results in advent of a stable nonlayered secondary ferromagnetic phase in the form of CrTe (T~ 160 K) in the parent vdW magnetic semiconductor CrGeTe (T~ 69 K). In addition, the magnetic anisotropy energy (MAE) enhances in the hybrid by an order from the weakly anisotropic pristine CrGeTe crystal, increasing the stability of the FM ground state with time. Comparing with the freshly prepared CrGeTe, the coexistence of the two ferromagnetic phases in the time elapsed bulk crystal is confirmed through systematic investigation of crystal structure along with detailed dc/ac magnetic susceptibility, specific heat, and magnetotransport measurement. To capture the concurrence of the two ferromagnetic phases in a single material, Ginzburg-Landau theory with two independent order parameters (as magnetization) with a coupling term can be introduced. In contrast to rather common poor environmental stability of the vdW magnets, our results open possibilities of finding air-stable novel materials having multiple magnetic phases