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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Revealing the electronic structure of van der Waals antiferromagnetic NiPS 3 through synchrotron-based 𝜇-ARPES and alkali metal dosing

Antiferromagnetic NiPS 3 has recently emerged as a quantum material of considerable interest, thanks to the discovery of multiple new couplings involving electrons, spins, orbitals, phonons, and magnons. However, controversies and open questions persist concerning the fundamental origins of these couplings. A critical piece of information required to advance the understanding is the precise electronic band structure of NiPS 3 . Angle-resolved photoemission spectroscopy (ARPES), combined with alkali metal dosing (AMD), can enable us to directly observe the subtle electronic states that appear around the Fermi surface, offering valuable insights into the intriguing quantum properties and interplays of the examined material. Here, in this study, we present a comprehensive characterization and analysis of the band structure of van der Waals layered antiferromagnet NiPS 3 , leveraging state-of-the-art μ-ARPES measurements supported by density functional theory (DFT) calculations. Theoretical DFT results identify the orbital contributions to the observed bands, providing a precise understanding of the experimental ARPES data. Crucially, AMD enables the observation of conduction band and defect-related states above the valence band maximum in NiPS 3 . Furthermore, temperature dependent ARPES results across the Néel transition temperature of NiPS 3 reveal that the paramagnetic and antiferromagnetic phases have nearly identical band structures, underlining the highly localized character of Ni d states. These findings substantially deepen our understanding of the electronic properties of NiPS 3 and lay a vital foundation for exploring the intriguing quantum phenomena it exhibits.

Cao, Yifeng [Boston Univ., MA (United States); Law↗
DOE OSTI2025

Ultranarrow electroluminescence from magnetic excitons in the van der Waals antiferromagnetic semiconductor NiPS 3

Electrically driven light emission from two-dimensional (2D) semiconducting materials has enabled numerous optoelectronic technologies, including light-emitting diodes, solid-state lasers, and single-photon sources for quantum communication. Here we report ultranarrow electroluminescence from the magnetic excitonic state of the van der Waals antiferromagnetic semiconductor NiPS 3 . This electroluminescence is enabled by the fabrication of gate-tunable NiPS 3 devices that remain electrically conductive below the antiferromagnetic ordering temperature of 155 K, ultimately allowing field-effect mobilities of 1.3 cm 2 V –1 s –1 and 4.5 cm 2 V –1 s –1 to be directly measured at room temperature and 7 K, respectively. By applying a high-frequency square wave voltage to the gate electrode of the resulting field-effect transistors, electroluminescence is capacitively induced from the magnetic excitons of NiPS 3 . Due to the coupling of these excitons with the underlying NiPS 3 antiferromagnetic order, the electroluminescence has an ultranarrow linewidth of 1 meV and a high degree of linear polarization (ρ = 0.78). In addition to facilitating fundamental studies of the coupling between spin states and excitons in van der Waals magnetic semiconductors, this work will accelerate the development of emerging 2D opto-spintronic applications.

two-dimensional materials↗
DOE OSTI2024

Field-induced spin polarization in the lightly Cr-substituted layered antiferromagnet NiP S 3

Tuning magnetic properties in layered magnets is an important route to realize novel phenomenon related to two-dimensional (2D) magnetism. Recently, tuning antiferromagnetic (AFM) properties through substitution and intercalation techniques has been widely studied in MPX 3 compounds. Interesting phenomena, such as diverse AFM structures and even the signatures of ferrimagnetism, have been reported. However, long-range ferromagnetic (FM) ordering has remained elusive. Here, in this work, we explored the magnetic properties of the Cr-substituted NiP S 3 . We found that Cr substitution is extremely efficient in controlling spin orientation in NiP S 3 . Our study reveals a field-induced spin polarization in lightly (9%) Cr-substituted NiP S 3 , which is likely attributed to the attenuation of AFM interactions and magnetic anisotropy due to Cr doping. Our work provides a possible strategy to achieve FM phase in AFM MPX 3 , which could be useful for investigating 2D magnetism as well as potential device applications.

2-dimensional systems↗
DOE OSTI2025

Characteristic exciton energy scales in antiferromagnetic NiPS 3

Two-dimensional antiferromagnets are promising materials for spintronics. The van der Waals antiferromagnet NiPS 3 has attracted extensive interest due to its ultranarrow exciton feature which is closely linked with the magnetic ordering. Here, we use time-resolved terahertz spectroscopy to investigate photoexcited carriers in NiPS 3 . We identify the onset of interband transitions and estimate the exciton dissociation energy from the excitation wavelength and fluence dependence of the transient spectral weight. Furthermore, our results provide key insights to quantify the exciton characteristics and validate the band structure for NiPS 3 .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Elucidating the Role of Dimensionality on the Electronic Structure of the Van der Waals Antiferromagnet NiPS 3

Abstract The sustained interest in investigating magnetism in the 2D limit of insulating antiferromagnets is driven by the possibilities of discovering, or engineering, novel magnetic phases through layer stacking. However, due to the difficulty of directly measuring magnetic interactions in 2D antiferromagnets, it is not yet understood how intra layer magnetic interactions in insulating , strongly correlated, materials can be modified through layer proximity. Herein, the impact of reduced dimensionality in the model van der Waals antiferromagnet NiPS 3 is explored by measuring electronic excitations in exfoliated samples using Resonant Inelastic X‐ray Scattering (RIXS). The resulting spectra shows systematic broadening of NiS 6 multiplet excitations with decreasing layer count from bulk down to three atomic layers (3L). It is shown that these trends originate from a decrease in transition metal‐ligand and ligand–ligand hopping integrals, and by charge‐transfer energy evolving from Δ = 0.83 eV in the bulk to 0.37 eV in 3L NiPS 3 . Relevant intralayer magnetic exchange integrals computed from the electronic parameters exhibit a decrease in the average interaction strength with thickness. This study underscores the influence of inter layer electronic interactions on intra layer ones in insulating magnets, indicating that magnetic Hamiltonians in few‐layer insulating magnets can greatly deviate from their bulk counterparts.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Emergence of ferrimagnetism in Li-intercalated NiPS 3

AbstractIntercalation has become a powerful approach to tune the intrinsic properties and introduce novel phenomena in layered materials. Intercalating van der Waals (vdW) magnetic materials is a promising route to engineer the low-dimensional magnetism. Recently, metal thiophosphates, MPX 3 , has been widely studied because their magnetic orders are highly tunable and persist down to the two-dimensional limit. In this work, we used electrochemical technique to intercalate Li into NiPS 3 single crystals and found the emergence of ferrimagnetism at low temperature in Li-intercalated NiPS 3 . Such tuning of magnetic properties highlights the effectiveness of intercalation, providing a novel strategy to manipulate the magnetism in vdW magnets.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Electronic Raman scattering in the 2D antiferromagnet NiPS 3

Correlated-electron systems have long been an important platform for various interesting phenomena and fundamental questions in condensed matter physics. As a pivotal process in these systems, d-d transitions have been suggested as a key factor toward realizing optical spin control in two-dimensional (2D) magnets. However, it remains unclear how d-d excitations behave in quasi-2D systems with strong electronic correlation and spin-charge coupling. Here, we present a systematic electronic Raman spectroscopy investigation on d-d transitions in a 2D antiferromagnet—NiPS 3 , from bulk to atomically thin samples. Two electronic Raman modes originating from the scattering of incident photons with d electrons in Ni 2+ ions are observed at ~1.0 eV. This electronic process persists down to trilayer flakes and exhibits insensitivity to the spin ordering of NiPS 3 . Our study demonstrates the utility of electronic Raman scattering in investigating the unique electronic structure and its coupling to magnetism in correlated 2D magnets.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Pressure-Induced Insulator–Metal Transition in Two-Dimensional Mott Insulator NiPS 3

The pressure-induced insulator to metal transition (IMT) of layered magnetic nickel phosphorous tri-sulfide NiPS 3 was studied in-situ under quasi-uniaxial conditions by means of electrical resistance (R) and X-ray diffraction (XRD) measurements. This sluggish transition is shown to occur at 35 GPa. Transport measurements show no evidence of superconductivity to the lowest measured temperature (~2 K). The structure results presented here differ from earlier in-situ work that subjected the sample to a different pressure state, suggesting that in NiPS 3 the phase stability fields are highly dependent on strain. Furthermore, it is suggested that careful control of the strain is essential when studying the electronic and magnetic properties of layered van der Waals solids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Zr(NiP)2 by Materials Project

Zr(NiP)2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Zr2+ is bonded in a distorted body-centered cubic geometry to eight equivalent P3- atoms. All Zr–P bond lengths are 2.85 Å. Ni2+ is bonded to four equivalent P3- atoms to form a mixture of edge and corner-sharing NiP4 tetrahedra. All Ni–P bond lengths are 2.24 Å. P3- is bonded in a 9-coordinate geometry to four equivalent Zr2+, four equivalent Ni2+, and one P3- atom. The P–P bond length is 2.25 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Nb5(NiP)4 by Materials Project

Nb5(NiP)4 crystallizes in the tetragonal I4/m space group. The structure is three-dimensional. there are two inequivalent Nb sites. In the first Nb site, Nb is bonded in a 5-coordinate geometry to five equivalent P atoms. There are a spread of Nb–P bond distances ranging from 2.59–2.72 Å. In the second Nb site, Nb is bonded in a square co-planar geometry to four equivalent P atoms. All Nb–P bond lengths are 2.65 Å. Ni is bonded in a 3-coordinate geometry to three equivalent P atoms. There are two shorter (2.22 Å) and one longer (2.27 Å) Ni–P bond lengths. P is bonded in a 9-coordinate geometry to six Nb and three equivalent Ni atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Th(NiP)2 by Materials Project

Th(NiP)2 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Th4+ is bonded in a 7-coordinate geometry to seven P3- atoms. There are a spread of Th–P bond distances ranging from 2.92–3.10 Å. There are two inequivalent Ni1+ sites. In the first Ni1+ site, Ni1+ is bonded to four P3- atoms to form a mixture of corner and edge-sharing NiP4 tetrahedra. There are two shorter (2.26 Å) and two longer (2.30 Å) Ni–P bond lengths. In the second Ni1+ site, Ni1+ is bonded to four P3- atoms to form a mixture of corner and edge-sharing NiP4 tetrahedra. There are a spread of Ni–P bond distances ranging from 2.21–2.31 Å. There are two inequivalent P3- sites. In the first P3- site, P3- is bonded in a 4-coordinate geometry to three equivalent Th4+ and four Ni1+ atoms. In the second P3- site, P3- is bonded in a 8-coordinate geometry to four equivalent Th4+ and four Ni1+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on NiP by Materials Project

NiP is Millerite-like structured and crystallizes in the orthorhombic Pbca space group. The structure is three-dimensional. Ni2+ is bonded in a 5-coordinate geometry to five equivalent P2- atoms. There are a spread of Ni–P bond distances ranging from 2.25–2.33 Å. P2- is bonded in a 5-coordinate geometry to five equivalent Ni2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Th(NiP)2 by Materials Project

Th(NiP)2 crystallizes in the tetragonal P4/nmm space group. The structure is three-dimensional. Th4+ is bonded in a 8-coordinate geometry to eight P3- atoms. There are four shorter (3.07 Å) and four longer (3.09 Å) Th–P bond lengths. There are two inequivalent Ni1+ sites. In the first Ni1+ site, Ni1+ is bonded in a 5-coordinate geometry to five P3- atoms. There are four shorter (2.29 Å) and one longer (2.34 Å) Ni–P bond lengths. In the second Ni1+ site, Ni1+ is bonded to four equivalent P3- atoms to form a mixture of corner and edge-sharing NiP4 tetrahedra. All Ni–P bond lengths are 2.36 Å. There are two inequivalent P3- sites. In the first P3- site, P3- is bonded in a 5-coordinate geometry to four equivalent Th4+ and five Ni1+ atoms. In the second P3- site, P3- is bonded in a 4-coordinate geometry to four equivalent Th4+ and four equivalent Ni1+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on NiPS by Materials Project

NiPS is Spinel-like structured and crystallizes in the cubic P2_13 space group. The structure is three-dimensional. Ni3+ is bonded to three equivalent P1- and three equivalent S2- atoms to form NiP3S3 octahedra that share corners with twelve equivalent NiP3S3 octahedra, corners with three equivalent PNi3S tetrahedra, and corners with three equivalent SNi3P tetrahedra. The corner-sharing octahedral tilt angles are 65°. All Ni–P bond lengths are 2.29 Å. All Ni–S bond lengths are 2.35 Å. P1- is bonded to three equivalent Ni3+ and one S2- atom to form PNi3S tetrahedra that share corners with three equivalent NiP3S3 octahedra, corners with six equivalent PNi3S tetrahedra, and corners with nine equivalent SNi3P tetrahedra. The corner-sharing octahedral tilt angles are 77°. The P–S bond length is 2.15 Å. S2- is bonded to three equivalent Ni3+ and one P1- atom to form SNi3P tetrahedra that share corners with three equivalent NiP3S3 octahedra, corners with six equivalent SNi3P tetrahedra, and corners with nine equivalent PNi3S tetrahedra. The corner-sharing octahedral tilt angles are 77°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Tm(NiP)2 by Materials Project

Tm(NiP)2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Tm3+ is bonded in a distorted body-centered cubic geometry to eight equivalent P3- atoms. All Tm–P bond lengths are 2.95 Å. Ni+1.50+ is bonded to four equivalent P3- atoms to form a mixture of edge and corner-sharing NiP4 tetrahedra. All Ni–P bond lengths are 2.26 Å. P3- is bonded in a 9-coordinate geometry to four equivalent Tm3+, four equivalent Ni+1.50+, and one P3- atom. The P–P bond length is 2.27 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Li(NiP)2 by Materials Project

Li(NiP)2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Li1+ is bonded to eight equivalent P+2.50- atoms to form LiP8 hexagonal bipyramids that share corners with sixteen equivalent NiP4 tetrahedra, edges with four equivalent LiP8 hexagonal bipyramids, edges with eight equivalent NiP4 tetrahedra, and faces with four equivalent LiP8 hexagonal bipyramids. All Li–P bond lengths are 2.88 Å. Ni2+ is bonded to four equivalent P+2.50- atoms to form NiP4 tetrahedra that share corners with eight equivalent LiP8 hexagonal bipyramids, corners with four equivalent NiP4 tetrahedra, edges with four equivalent LiP8 hexagonal bipyramids, and edges with four equivalent NiP4 tetrahedra. All Ni–P bond lengths are 2.24 Å. P+2.50- is bonded in a 9-coordinate geometry to four equivalent Li1+, four equivalent Ni2+, and one P+2.50- atom. The P–P bond length is 2.16 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Direct Observation and Analysis of Low-Energy Magnons with Raman Spectroscopy in Atomically Thin NiPS 3

van der Waals (vdW) magnets have rapidly emerged as a fertile playground for fundamental physics and exciting applications. Despite the impressive developments over the past few years, technical limitations pose a severe challenge to many other potential breakthroughs. High on the list is the lack of suitable experimental tools for studying spin dynamics on atomically thin samples. Here, Raman scattering techniques are employed to directly observe the low-lying magnon (~1 meV) even in bilayer NiPS 3 . Further, the advantage is that it offers excellent energy resolutions far better on low-energy sides than most inelastic neutron spectrometers can offer. More importantly, with appropriate theoretical analysis, the polarization dependence of the Raman scattering by those low-lying magnons also provides otherwise hidden information on the dominant spin-exchange scattering paths for different magnons. By comparing with high-resolution inelastic neutron scattering data, these low-energy Raman modes are confirmed to be indeed of magnon origin. Because of the different scattering mechanisms involved in inelastic neutron and Raman scattering, this information is fundamental in pinning down the final spin Hamiltonian. This work demonstrates the capability of Raman spectroscopy to probe the genuine two-dimensional spin dynamics in atomically thin vdW magnets, which can provide insights that are obscured in bulk spin dynamics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗