arXiv subjects

M. Majumder

Publications and source records attributed to M. Majumder.

At least 19 recordsLinked to original sources

arXiv2026

Spin-orbit-entangled frustrated magnetism in fcc Ba$_2$(Yb,Nd)NbO$_6$ double perovskites

The search for candidate Kitaev materials has largely focused on 4$d$ and 5$d$ transition-metal compounds with various lattice geometries. In contrast, investigations of rare-earth 4$f$ systems have thus far been restricted mainly to honeycomb and triangular lattices. In this work, we investigate the rare-earth-based double perovskites Ba$_2$YbNbO$_6$ and Ba$_2$NdNbO$_6$, which crystallize in a face-centered cubic structure. Magnetization and heat-capacity measurements establish isolated ${j_{\rm eff}} = 1/2$ Kramers doublet ground states arising from strong spin-orbit coupling (SOC) and crystal electric-field effects, which are further supported by density-functional theory calculations. Millikelvin-temperature thermodynamic measurements reveal long-range magnetic order with moderate frustration in both compounds. The emergence of magnetic order may be understood within an order-by-disorder scenario, as theoretically proposed for rare-earth fcc lattices with finite Kitaev interactions. Our results thus identify Ba$_2$YbNbO$_6$ and Ba$_2$NdNbO$_6$ as promising rare-earth spin-orbit-entangled magnets and motivate further experimental and theoretical investigations aimed at determining the complete exchange tensor to elucidate the microscopic origin of the underlying magnetic interactions.

cond-mat.str-el↗

arXiv2026

Evidence for Multiband Superconductivity in 2H-NbSeS

The nature of superconductivity in 2H-NbSe2 has generated sustained debate in the recent past. While angle resolved photoemission spectroscopy data have been interpreted as evidence for multiband superconductivity, the data from scanning tunneling microscope experiments relate to strongly anisotropic single-band superconductivity. In the later case, the charge density wave (CDW) order mimics the multigap character. Because the CDW reconstructs the Fermi surface and modifies the superconducting gap distribution, disentangling intrinsic multiband pairing from CDW-related effects is challenging. To address this issue, we investigate single-crystalline 2H-NbSeS, a mixed-chalcogen analogue of 2H-NbSe2 in which random Se/S substitution suppresses long-range CDW order while preserving the layered crystal structure P63/mmc. The material becomes superconducting below 6.0 K with moderate magnetic anisotropy. The upper critical field exhibits a pronounced upward curvature that cannot be described within a single-band framework but is well captured by a dirty-limit two-band model with a large diffusivity ratio. This indicates strong band-dependent scattering. The in-plane upper critical field exceeds the weak-coupling Pauli limit. Measurements of the lower critical field, superfluid density, and electronic specific heat are consistent with an interpretation of a fully gapped superconducting state with two nodeless gaps of different magnitudes.

cond-mat.supr-con↗

arXiv2026

Disorder-driven coexistence of distinct dynamical states in frustrated Sr$_3$CuNb$_2$O$_9$: a microscopic $\mu$SR and $^{93}$Nb NMR study

Despite recent progress in identifying the exotic random singlet (RS) state in disordered frustrated magnets as a distinct correlated phase, three-dimensional (3D) realizations remain scarce. Sr$_3$CuNb$_2$O$_9$ was proposed to be one of such 3D frustrated systems with magnetic site disorder hosting an RS ground state. Here, we report a detailed microscopic investigation of Sr$_3$CuNb$_2$O$_9$ employing muon spin relaxation ($\mu$SR) and $^{93}$Nb nuclear magnetic resonance (NMR) techniques. The $\mu$SR zero-field relaxation rate reveals a power-law divergence of the relaxation rate as a function of temperature. Also, a power-law divergence is present in the relaxation rate as a function of applied longitudinal field, consistent with the formation of an RS phase. The $^{93}$Nb NMR spectra unambiguously resolve two components with distinct local magnetic environments, whose nature is further elucidated through spin-lattice relaxation measurements analyzed via an inverse Laplace transform (ILT) of the nuclear magnetization recovery. The relaxation-rate distribution obtained from ILT reveals two well-separated channels: a fast component, $(1/T_1)_{\mathrm{fast}}$, and a slow component, $(1/T_1)_{\mathrm{slow}}$. Both components follow distinct power-law temperature dependences ($T^{\alpha}$), with $\alpha = 0.6$ and $1.1$ for the fast and slow channels, respectively. The combined spectral and relaxation data demonstrate that the fast channel qualitatively represents an RS-like state, whereas the slow channel exhibits quantum spin liquid (QSL) like behavior, thereby establishing the microscopic coexistence of RS and QSL-like phases in Sr$_3$CuNb$_2$O$_9$.

cond-mat.str-el↗

arXiv2026

Proximate quantum spin liquid state in the frustrated HoInCu$_4$ metal

We conducted a comprehensive and comparative muon-spin relaxation and rotation ($\mu$SR) investigation on two fcc-lattice metallic compounds, HoCdCu$_4$ ($T_\mathrm{N}\approx 8$ K) and HoInCu$_4$ ($T_\mathrm{N}\approx 0.76$ K), to elucidate the nature of their magnetic ground states and the role of frustration in stabilizing them. Our $\mu$SR results reveal that, in contrast to HoCdCu$_4$, strong magnetic frustration exists in HoInCu$_4$. Notably, in HoInCu$_{4}$, only 30% of the Ho-moments participate in the static magnetic ordering below $T_\mathrm{N}$, while the remaining 70% of the Ho-moments exhibit dynamic correlations and persistent spin dynamics down to 0.3 K, resembling a quantum spin-liquid (QSL) behavior. By contrast, in HoCdCu$_{4}$, all the Ho-moments contribute to the magnetic order below $T_\mathrm{N}$. Furthermore, in HoInCu$_{4}$, the temperature dependence of the relaxation rate indicates the presence of quantum critical fluctuations in the paramagnetic state near $T_\mathrm{N}$, suggesting the proximity to a quantum critical point (QCP). These observations suggest that the ground state of HoInCu$_{4}$ is a proximate quantum spin liquid (PQSL), a state that has not been reported before in frustrated metallic systems. Our $\mu$SR findings are further corroborated by recent inelastic neutron results on HoInCu$_4$, which show similarities to other insulating PQSL candidates, thus reinforcing our conclusions.

cond-mat.str-el↗

arXiv2026

Quantum spin liquid ground state with the evidence of roton-like excitations at elevated temperatures in the triangular-lattice delafossite YbCuSe$_2$

We present a comprehensive experimental investigation of the temperature evolution of magnetic states in triangular-lattice delafossite YbCuSe$_2$. Magnetization measurements on high-quality single crystals reveal easy-plane anisotropy. Specific heat, magnetization, and muon spin relaxation ($\mu$SR) establish the absence of magnetic order or spin freezing down to 0.03 K ($\leq J_{\mathrm{avg}}/250$), demonstrating a dynamically fluctuating quantum spin liquid (QSL) ground state. Thermodynamic measurements uncover multiple characteristic energy scales at $T_H \approx 4.5$ K, $T_L \approx 1.8$ K, and $T^* \approx 0.7$ K. Below $T^*$, $\mu$SR detects a dynamical phase separation in which the majority of the spins are forming a QSL state whereas the remaining spins form a sporadic, disorder-induced state decoupled from the dominant QSL component. Remarkably, the unconventional temperature dependence of the $\mu$SR relaxation rate indicates roton-like excitations emerging between $T_H$ and $T_L$, a feature not previously observed in any QSL system, preceding the stabilization of the low-temperature QSL at 0.3 K. These findings identify YbCuSe$_2$ as a unique QSL platform, providing valuable insights for further experimental and theoretical exploration.

cond-mat.str-el↗

arXiv2025

Microscopic evidence of a field-induced critical spin-liquid state in a frustrated metal

A field-induced quantum spin liquid (QSL) state is an extraordinary phenomenon, hitherto unobserved in metallic frustrated compounds. Recent bulk measurements have revealed intriguing field-induced magnetic states in metallic frustrated CePdAl. However, the nature of these field-induced states, potentially including a QSL state, remains unclear due to the lack of detailed microscopic investigation. To elucidate these field-induced states, we employed the transverse-field muon spin relaxation/rotation (TF-$\mu$SR) technique, applying various magnetic fields parallel to the c-axis in single-crystalline CePdAl over a broad temperature range (100~K-100~mK). Our $\mu$SR data indicate that field-induced low-temperature states for fields B$\leq B_{c2}(=3.4~T)$ exhibit long-range magnetic order, whereas for B>$B_{c2}$ they yield contrasting behavior. Notably, at 3.75 T, the transverse relaxation rate ($\lambda_T$) diverges following a power-law dependence below 800~mK along with an indication of finite frustration, whereas the Knight shift is temperature independent. These observations corroborate the signature of a critical spin-liquid (CSL) with antiferromagnetic spin fluctuations. Furthermore, at 4.3 T, a non-Fermi liquid state is observed where frustration is absent. This comprehensive microscopic study strongly suggests the existence of a CSL state in a metallic frustrated system.

cond-mat.str-el↗

arXiv2025

Evidence for magnetoelastic coupling and chiral magnetic ground state in quasi-van der Waals tr-Cr$_{1.22}$Te$_{2}$

Trigonal tr-Cr$_{1+\delta}$Te$_{2}$ is a well-known ferromagnetic material that has recently drawn much attention due to the discovery of zero-field skyrmion state, unusual anomalous Hall effect, topological Hall effect, and topological Nernst effect. This quasi-van der Waals (vdW) layered material with intercalated Cr atoms possesses many peculiar features that depend on the amount of Cr intercalation, although the microscopic magnetic ground state is still elusive. We reveal the structural and magnetic properties of tr-Cr$_{1.22}$Te$_{2}$ by low-temperature x-ray diffraction, magnetization, temperature-dependent Raman spectroscopy, and single-crystal neutron diffraction studies. Magnetization measurements under small applied magnetic field indicate two successive magnetic transitions, one from a ferromagnetic (FM) state to an antiferromagnetic (AFM) state (T$_\mathrm{C}=197$ K), and second from AFM to a paramagnetic state (T$_\mathrm{N}=211$ K). The FM transition is sharp with a strong presence of magnetoelastic coupling, but is not accompanied by any structural phase transition. The magnetic structure obtained from zero-field single crystal neutron diffraction reveals that the Cr1 and Cr2 moments are ferromagnetically aligned along the c-axis, while the Cr3 and intercalated Cr4 atoms induce an AFM component in the ab-plane leading to an umbrella-like spin structure which possesses a finite spin chirality. The presence of a finite spin chirality is responsible for the observation of the topological Hall effect (THE).

cond-mat.str-el↗

arXiv2024

Hydrostatic and chemical pressure driven crossover from commensurate to the incommensurate state of the Weyl semimetal Mn$_{3+x}$Sn$_{1-x}$

The observation of large intrinsic anomalous Hall conductivity (AHC) in the non-collinear antiferromagnetic (AFM) phase of the Weyl semimetal Mn$_3$Sn generates enormous interest in uncovering the entanglement between the real space magnetic ordering and the momentum space band structure. Previous studies show that changes in the magnetic structure induced by the application of hydrostatic and chemical pressure can significantly affect the AHC of Mn$_{3+x}$Sn$_{1-x}$ system. Here, we employ the muon spin relaxation/rotation ($\mu^+$SR) technique to systematically investigate the evolution of different magnetic states in the Mn$_{3+x}$Sn$_{1-x}$ as a function of hydrostatic and chemical pressure. We find two muon sites experimentally, which is also supported by our \textit{ab initio} calculations. Our $\mu^+$SR experiments affirm that the $x = 0.05$ compound exhibits a commensurate magnetic state throughout the magnetically ordered phase below the Neel temperature $T_N \approx 420$~K in ambient pressure. In contrast, we observe an incommensurate magnetic state below $T_{IC} \sim 175$~K when a hydrostatic pressure of 1.5~GPa is applied. A similar transition from the commensurate to incommensurate state is also found with chemical pressure for $x = 0.04$ and $x = 0.03$, using $\mu^+$SR and elastic neutron scattering experiments. Using band structure calculations, we have shown the emergence of Fermi nesting in Mn$_3$Sn and the subsequent development of incommensurate magnetic ordering under hydrostatic/chemical pressure.

cond-mat.str-el↗

arXiv2024

Evidence of quantum spin liquid state in a Cu$^{2+}$-based $S = 1/2$ triangular lattice antiferromagnet

The layered triangular lattice owing to $1:2$ order of $B$ and $B'$ sites in the triple perovskite $A_3 B B'_2$O$_9$ family provides an enticing domain for exploring the complex phenomena of quantum spin liquids (QSLs). We report a comprehensive investigation of the ground state properties of Sr$_3$CuTa$_2$O$_9$ that belongs to the above family, by employing magnetization, specific heat, and muon spin relaxation ($\mu$SR) experiments down to the lowest temperature of 0.1~K. Analysis of the magnetic susceptibility indicates that the spin-lattice is a nearly isotropic $S = 1/2$ triangular lattice. We illustrate the observation of a gapless QSL, in which conventional spin ordering or freezing effects are absent, even at temperatures more than two orders of magnitude smaller than the exchange energy ($J_{\rm CW}/k_{\rm B} \simeq -5.04$~K). Magnetic specific heat in zero-field follows a power law, $C_{\rm m} \sim T^\eta$, below 1.2~K with $\eta \approx 2/3$, which is consistent with a theoretical proposal of the presence of spinon Fermi surface. Below 1.2~K, the $\mu$SR relaxation rate shows no temperature dependence, suggesting persistent spin dynamics as expected for a QSL state. Delving deeper, we also analyze longitudinal field $\mu$SR spectra revealing strong dynamical correlations in the spin-disordered ground state. All of these highlight the characteristics of spin entanglement in the QSL state.

cond-mat.str-el↗

arXiv2024

Evidence of random spin-singlet state in a three-dimensional quantum spin liquid candidate Sr$_3$CuNb$_2$O$_9$

Disorder is ubiquitous in any quantum many-body system and is usually considered to be an obstacle to the elucidation of the underlying physics of complex systems, but its presence can often introduce exotic phases of matter that cannot generally be realized in a clean system. We report here a detailed experimental and theoretical study of magnetic properties of highly disordered Sr$_3$CuNb$_2$O$_9$ material which exhibits random site mixing between Cu and Nb. The magnetic moments (Cu$^{2+}$) are arranged in a quasi-cubic (three-dimensional) manner, leading to a high degree of frustration with a Curie-Weiss temperature ($\theta_{CW}$) of about -60 K without any long-range magnetic ordering down to 466 mK. These observations suggest that Sr$_3$CuNb$_2$O$_9$ is a candidate for a quantum spin liquid. More interestingly, the susceptibility ($\chi = M/\mu_0H$) and the $C_m/T$ ($C_m$ is the magnetic part of the heat capacity) follow a power-law behavior with decreasing temperature. In addition, $M(T,\mu_0H)$ and $C_m(T,\mu_0H)/T$ show scaling relationships over a wide temperature and field range. This unusual behavior with respect to the conventional behavior of a QSL can be discussed qualitatively as the coexistence of a disorder-induced random spin singlet (RSS) state and a QSL state. A quantitative description has been given by numerical calculations considering a power-law probability distribution $P(J) \propto J^{-\gamma}$ ($J$ is the exchange interaction) of random spin singlets. The parameters extracted from the numerical calculations are in excellent agreement with the experimental data. Furthermore, the analytical results are also consistent with the power-law and scaling behavior of $\chi$ and $C_m(T,\mu_0H)/T$ as a whole. Thus, our comprehensive experimental and theoretical analysis provides evidence for the stabilization of the RSS state in a three-dimensional lattice.

cond-mat.str-el↗

arXiv2024

Frustration-induced quantum criticality in Ni-doped CePdAl as revealed by the $μ$SR technique

In CePdAl, the 4$f$ moments of cerium arrange to form a geometrically frustrated kagome lattice. Due to frustration, in addition to Kondo- and Ruderman-Kittel-Kasuya-Yosida interactions, this metallic system shows a long-range magnetic order (LRO) with a $T_{\rm N}$ of only 2.7\,K. Upon Ni doping at the Pd sites, $T_{\rm N}$ is further suppressed, to reach zero at a critical concentration $x_c \approx 0.15$. Here, by using muon-spin relaxation and rotation ($μ$SR), we investigate CePd${1-x}$Ni$_x$Al at a local level for five different Ni-concentrations, both above and below $x_c$. Like the parent CePdAl compound, for $x = 0.05$, we observe an incommensurate LRO, which turns into a quasi-static magnetic order for $x = 0.1$ and 0.14. More interestingly, away from $x_c$, for $x = 0.16$ and 0.18, we still observe a non-Fermi liquid regime, evidenced by a power-law divergence of the longitudinal relaxation at low temperatures. In this case, longitudinal field measurements exhibit a time-field scaling, indicative of a cooperative spin dynamics that persists for $x > x_c$. Furthermore, like the externally applied pressure, the chemical pressure induced by Ni doping suppresses the region below $T^*$, characterized by a spin-liquid like dynamical behavior. Our results suggest that the magnetic properties of CePdAl are similarly affected by the hydrostatic- and the chemical pressure. We also confirm that the unusual non-Fermi liquid regime (compared with conventional quantum critical systems) is due to the presence of frustration that persists up to the highest Ni concentrations.

cond-mat.str-el↗

arXiv2022

Spin-liquid signatures in the quantum critical regime of pressurized CePdAl

CePdAl is a prototypical frustrated Kondo lattice with partial long-range order (LRO) at $T_\mathrm{N}=2.7$ K. Previous bulk experiments under hydrostatic pressure found signatures for a quantum critical regime that extends from $p_\mathrm{c} \approx 0.9$ GPa, where LRO disappears, up to $\sim 1.7$ GPa. We employed extensive muon spin relaxation and rotation ($μ$SR) experiments under pressure. The continuous and complete suppression of LRO at $p_\mathrm{c}$ is confirmed. Above $T_\mathrm{N}(p)$ and beyond $p_\mathrm{c}$, an additional crossover scale $T^\ast(p)$ characterizes the change from pure to stretched exponential relaxation in zero field. Remarkably $T^\ast(p)$ agrees with previously determined signatures of entropy accumulation above LRO. This coincidence microscopically evidences fluctuating frustrated spins at $T\leq T^\ast$ with spin-liquid behavior. Power-law divergences of the temperature and longitudinal field dependences of the relaxation rate, with time-field scaling, at pressures between $p_c$ and 1.7 GPa characterize this regime as quantum critical.

cond-mat.str-el↗

arXiv2020

Field evolution of low-energy excitations in the hyperhoneycomb magnet $β$-Li$_2$IrO$_3$

$^7$Li nuclear magnetic resonance (NMR) and terahertz (THz) spectroscopies are used to probe magnetic excitations and their field dependence in the hyperhoneycomb Kitaev magnet $β$-Li$_2$IrO$_3$. Spin-lattice relaxation rate ($1/T_1$) measured down to 100\,mK indicates gapless nature of the excitations at low fields (below $H_c\simeq 2.8$\,T), in contrast to the gapped magnon excitations found in the honeycomb Kitaev magnet $α$-RuCl$_3$ at zero applied magnetic field. At higher temperatures in $β$-Li$_2$IrO$_3$, $1/T_1$ passes through a broad maximum without any clear anomaly at the Néel temperature $T_N\simeq 38$\,K, suggesting the abundance of low-energy excitations that are indeed observed as two peaks in the THz spectra, both correspond to zone-center magnon excitations. At higher fields (above $H_c$), an excitation gap opens, and a re-distribution of the THz spectral weight is observed without any indication of an excitation continuum, in contrast to $α$-RuCl$_3$ where an excitation continuum was reported.

cond-mat.str-el↗

arXiv2019

Competing magnetic correlations across the ferromagnetic quantum critical point in the Kondo system CeTi$_{1-x}$V$_x$Ge$_3$: $^{51}$V NMR as a local probe

$^{51}$V nuclear magnetic resonance (NMR) and magnetization studies on CeTi$_{1-x}$V$_x$Ge$_3$ have been performed to explore the evolution from the ferromagnetic ($x = 0.113$) to the antiferromagnetic Kondo lattice state ($x = 1$), with focus on the emergence of a possible ferromagnetic quantum critical point (FMQCP) at $x_c \approx 0.4$. From the temperature dependence of the nuclear spin-lattice relaxation rate, $1/T_1T$, and the Knight shift, \textit{K}, for $x=0.113$ and $x=1$ a considerable competition between ferro- and antiferromagnetic correlations is found. Around the critical concentration ($x = 0.35, 0.405$) quantum-critical spin fluctuations entail weak antiferromagnetic spin fluctuations admixed with ferromagnetic spin fluctuations. The FMQCP in CeTi$_{1-x}$V$_x$Ge$_3$ therefore is not purely ferromagnetic in nature.

cond-mat.str-el↗

arXiv2019

Anisotropic temperature-field phase diagram of single-crystalline $β$-Li$_2$IrO$_3$: magnetization, specific heat, and $^7$Li NMR study

Detailed magnetization, specific heat, and $^7$Li nuclear magnetic resonance (NMR) measurements on single crystals of the hyperhoneycomb Kitaev magnet $β$-Li$_2$IrO$_3$ are reported. At high temperatures, {\cred anisotropy of the magnetization is reflected by the different Curie-Weiss temperatures for different field directions}, in agreement with the combination of a ferromagnetic Kitaev interaction ($K$) and a negative off-diagonal anisotropy ($Γ$) as two leading terms in the spin Hamiltonian. At low temperatures, magnetic fields applied along $a$ or $c$ have only a weak effect on the system and reduce the Néel temperature from 38 K at 0 T to about 35.5 K at 14 T, with no field-induced transitions observed up to 58 T on a powder sample. In contrast, the field applied along $b$ causes a drastic reduction in the $T_N$ that vanishes around $H_c=2.8$ T giving way to a crossover toward a quantum paramagnetic state. $^7$Li NMR measurements in this field-induced state reveal a gradual line broadening and a continuous evolution of the line shift with temperature, suggesting the development of local magnetic fields. The spin-lattice relaxation rate shows a peak around the crossover temperature 40 K and follows power-law behavior below this temperature.

cond-mat.str-el↗

arXiv2018

Breakdown of magnetic order in the pressurized Kitaev iridate $β$-Li$_2$IrO$_3$

Temperature-pressure phase diagram of the Kitaev hyperhoneycomb iridate $β$-Li$_2$IrO$_3$ is explored using magnetization, thermal expansion, magnetostriction, and muon spin rotation ($μ$SR) measurements, as well as single-crystal x-ray diffraction under pressure and ab initio calculations. The Neel temperature of $β$-Li$_2$IrO$_3$ increases with the slope of 0.9 K/GPa upon initial compression, but the reduction in the polarization field $H_c$ reflects a growing instability of the incommensurate order. At 1.4 GPa, the ordered state breaks down upon a first-order transition giving way to a new ground state marked by the coexistence of dynamically correlated and frozen spins. This partial freezing in the absence of any conspicuous structural defects may indicate classical nature of the resulting pressure-induced spin liquid, an observation paralleled to the increase in the nearest-neighbor off-diagonal exchange $Γ$ under pressure.

cond-mat.str-el↗

arXiv2017

Persistent low-temperature spin dynamics in the mixed-valence iridate Ba$_{3}$InIr$_{2}$O$_{9}$

Using thermodynamic measurements, neutron diffraction, nuclear magnetic resonance, and muon spin relaxation, we establish putative quantum spin-liquid behavior in Ba$_3$InIr$_2$O$_9$, where unpaired electrons are localized on mixed-valence Ir$_2$O$_9$ dimers with Ir$^{4.5+}$ ions. Despite the antiferromagnetic Curie-Weiss temperature on the order of 10 K, neither long-range magnetic order nor spin freezing are observed down to at least 20 mK, such that spins are short-range correlated and dynamic over nearly three decades in temperature. Quadratic power-law behavior of both the spin-lattice relaxation rate and specific heat indicates the gapless nature of the ground state. We envisage that this exotic behavior may be related to an unprecedented combination of the triangular and buckled honeycomb geometries of nearest-neighbor exchange couplings in the mixed-valence setting.

cond-mat.str-el↗

arXiv2016

Commensurate and incommensurate magnetic order in spin-1 chains stacked on the triangular lattice in Li$_2$NiW$_2$O$_8$

We report thermodynamic properties, magnetic ground state, and microscopic magnetic model of the spin-1 frustrated antiferromaget Li$_{2}$NiW$_{2}$O$_{8}$ showing successive transitions at $T_{\rm N1}\simeq 18$ K and $T_{\rm N2}\simeq 12.5$ K in zero field. Nuclear magnetic resonance and neutron diffraction reveal collinear and commensurate magnetic order with the propagation vector $\mathbf k=(\frac12,0,\frac12)$ below $T_{\rm N2}$. The ordered moment of 1.8 $μ_B$ at 1.5 K is directed along $[0.89(9),-0.10(5),-0.49(6)]$ and matches the magnetic easy axis of spin-1 Ni$^{2+}$ ions, which is determined by the scissor-like distortion of the NiO$_6$ octahedra. Incommensurate magnetic order, presumably of spin-density-wave type, is observed in the region between $T_{\rm N2}$ and $T_{\rm N1}$. Density-functional band-structure calculations put forward a three-dimensional spin lattice with spin-1 chains running along the $[01\bar 1]$ direction and stacked on a spatially anisotropic triangular lattice in the $ab$ plane. We show that the collinear magnetic order in Li$_2$NiW$_2$O$_8$ is incompatible with the triangular lattice geometry and thus driven by a pronounced easy-axis single-ion anisotropy of Ni$^{2+}$.

cond-mat.mtrl-sci↗