Search

CrI$_3$ represents one of the most important van der Waals systems on the route to understanding two-dimensional magnetic phenomena. Being arranged in a specific layered structure it also provides a unique opportunity to investigate structural transformations in dimension-confined systems. CrI$_3$ is dimorphic and possesses a higher symmetry low-temperature phase, which is quite uncommon. It contrasts with vanadium trihalides which show a higher symmetry high-temperature. An explanation of this distinct behavior together with a large cycle-dependent transition hysteresis is still an open question. Our low-temperature X-ray diffraction study conducted on CrI$_3$ single crystals complemented by magnetization and specific heat measurements was focused mainly on specific features of the structural transition during cooling. Our results manifest that the structural transition during cooling relates to the formation of structural domains despite the lower symmetry structure transforming to a higher symmetry one. We propose that these domains could control the transition temperature and also the size of thermal hysteresis.

We studied magnetic states and phase transitions in the van der Waals antiferromagnet VBr3 by specific heat and magnetization measurements of single crystals in high magnetic fields and by ab initio density functional theory calculations focused on exchange interactions. The magnetization behavior resembles Ising antiferromagnets with magnetic moments kept in the out-of-plane direction by strong uniaxial magnetocrystalline anisotropy. The out-of-plane magnetic field induces a spin-flip metamagnetic transition, which is of first-order type at low temperatures while at higher temperatures the transition becomes continuous. The first-order and continuous transition segments in the field-temperature phase diagram meet at a tricritical point at = 12 K. The magnetization response to the in-plane field manifests a continuous spin-flop transition, which at 2 K terminates at a field mu0Hc = 27 T that can serve as an estimate of the anisotropy field in VBr3. The magnetization curves above the metamagnetic transition saturate at the same value of magnetic moment musat = 1.2 muB/f.u., which is much smaller than the spin-only (S = 1) moment of the V3+ ion. The reduced moment can be explained by the existence of a significant orbital magnetic moment antiparallel to the spin. The orbital moment is a key ingredient of a mechanism responsible for the observed large anisotropy. The exact energy evaluation of possible magnetic orders unambiguously shows that the magnetic ground state of VBr3 is the intralayer zigzag antiferromagnetic order that renders the antiferromagnetic ground state significantly more stable against the spin-flip transition than the other options. The calculations also predict that a minimal distortion of the Br ion sublattice causes a radical change of the orbital occupation in the ground state, connected with the formation of the orbital moment and the stability of magnetic order.

We use the synergy of infrared, terahertz, and Raman spectroscopies with DFT calculations to shed light on the magnetic and lattice properties of VI3. The structural transition at TS1 = 79 K is accompanied by a large splitting of polar phonon modes. Below TS1, strong ferromagnetic fluctuations are observed. The variations of phonon frequencies at 55 K induced by magnetoelastic coupling enhanced by spin-orbit interaction indicate the proximity of long-range ferromagnetic order. Below TC = 50 K, two Raman modes simultaneously appear and show dramatic softening in the narrow interval around the temperature TS2 of the second structural transition associated with the order-order magnetic phase transition. Below TS2, a magnon in the THz range appears in Raman spectra. The THz magnon observed in VI3 indicates the application potential of 2D van der Waals ferromagnets in ultrafast THz spintronics, which has previously been considered an exclusive domain of antiferromagnets., Comment: Accepted in Journal of Physical Chemistry Letters

Kitaev physics has recently attracted attention in condensed matter for its anticipated novel quantum spin liquid state. The thermal transport measurement is crucial for probing the novel features of charge-neutral quasiparticles. In this letter, we report a significant thermal Hall effect in $Na_2Co_2TeO_6$ (NCTO), a Kitaev quantum spin liquid candidate, when the magnetic field is applied along the out-of-plane direction of the honeycomb plane. The thermal conductivity ($\kappa_{xx}$) and thermal Hall conductivity ($\kappa_{xy}$) in NCTO reveal distinct magnetic field dependences below and above the Neel temperature ($T_N$) of 27 K. For $T>T_N$, $\kappa_{xx}$ has a monotonic decrease in the field dependence, while $\kappa_{xy}$ persists up to $T^*$ = 150 K. On the other hand, both $\kappa_{xx}$ and $\kappa_{xy}$ exhibit complex field dependence for $T

We grew high-quality single crystals of the 5f electron van der Waals compound UI$_3$ and investigated them by measurements of specific heat and magnetization as functions of temperature and magnetic field. UI$_3$ behaves as an antiferromagnet with a first-order magnetic phase transition at the Ne\'el temperature $T_N$ = 2.65 K. It is characterized by a sharp symmetric specific-heat peak which is gradually shifted to lower temperatures by increasing magnetic field applied along either the a- or b-axis. The behavior in magnetic fields reveals orthorhombic magnetocrystalline anisotropy with the hard magnetization direction along the c-axis. The 2-K a- and b-axis magnetization curves exhibit a metamagnetic transition at the critical field $H_c$ = 3 T and 1.8 T, respectively. In higher fields, when the long-range antiferromagnetism is suppressed by a metamagnetic transition, signs of short-range magnetic ordering of antiferromagnetic correlations in the paramagnetic state show up both in specific heat and magnetization. The anomalous S-shape field dependence of a-axis magnetization well above $H_c$ can be understood as the crossover from the correlated paramagnetic regime to the high-field polarized paramagnet. The magnetic phase diagrams for the magnetic field applied along the a- and b-axis, respectively, designed using the mentioned experimental results are presented. We have also found that the UI$_3$ crystals are easily cleavable which predisposes this material for direct investigation of 5f electron magnetism in the 2D limit on exfoliated atomically thin samples., Comment: Submitted to JALCOM

Most transition-metal trihalides are dimorphic. The representative chromium-based triad, CrCl3, CrBr3, CrI3, is characterized by the low-temperature phase adopting the trigonal BiI3 type while the structure of the high-temperature phase is monoclinic of AlCl3 type (C2/m). The structural transition between the two crystallographic phases is of the first-order type with large thermal hysteresis in CrCl3 and CrI3. We studied crystal structures and structural phase transitions of vanadium-based counterparts VCl3, VBr3, and VI3 by measuring specific heat, magnetization, and X-ray diffraction as functions of temperature and observed an inverse situation. In these cases, the high-temperature phase has a higher symmetry while the low-temperature structure reveals a lower symmetry. The structural phase transition between them shows no measurable hysteresis in contrast to CrX3. Possible relations of the evolution of the ratio c/a of the unit cell parameters, types of crystal structures, and nature of the structural transitions in V and Cr trihalides are discussed., Comment: 11 pages, 6 figures, 1 table. J. Phys.: Condens. Matter (2022)

Layered van-der-Waals 2D magnetic materials are of great interest in fundamental condensed-matter physics research, as well as for potential applications in spintronics and device physics. We present neutron powder diffraction data using new ultra-high-pressure techniques to measure the magnetic structure of Mott-insulating 2D honeycomb antiferromagnet FePS$_3$ at pressures up to 183 kbar and temperatures down to 80 K. These data are complemented by high-pressure magnetometry and reverse Monte Carlo modeling of the spin configurations. As pressure is applied, the previously-measured ambient-pressure magnetic order switches from an antiferromagnetic to a ferromagnetic interplanar interaction, and from 2D-like to 3D-like character. The overall antiferromagnetic structure within the $ab$ planes, ferromagnetic chains antiferromagnetically coupled, is preserved, but the magnetic propagation vector is altered from $(0\:1\:\frac{1}{2})$ to $(0\:1\:0)$, a halving of the magnetic unit cell size. At higher pressures, coincident with the second structural transition and the insulator-metal transition in this compound, we observe a suppression of this long-range-order and emergence of a form of magnetic short-range order which survives above room temperature. Reverse Monte Carlo fitting suggests this phase to be a short-ranged version of the original ambient pressure structure - with a return to antiferromagnetic interplanar correlations. The persistence of magnetism well into the HP-II metallic state is an observation in seeming contradiction with previous x-ray spectroscopy results which suggest a spin-crossover transition., Comment: Manuscript currently under review in Phys Rev X

Pressure induced superconductivity in non-centrosymmetric CeRhSi$_{3}$ and CeIrSi$_{3}$ compounds has attracted significant attention of the scientific community since its discovery 15 years ago. Up-to-date, all reported experimental results were obtained employing the hybrid-cylinder piston pressure cells with a maximum reachable pressure of 3 GPa. Present study focuses on the superconducting state at higher, so far unreported, pressures using the Bridgman anvil cell and a CeRhSi$_{3}$ single crystal synthesized by the Sn-true-flux method. The initial increase of superconducting critical temperature from 0.4 K at 1.1 GPa to 1.1 K at 2.4 GPa is followed by a gradual suppression of SC state upon increasing the pressure above 3.0 GPa, forming a typical dome. The pressure induced superconductivity is expected to be completely suppressed in the pressure region between 4.5 and 5.0 GPa. Temperature dependence of electrical resistivity in constant magnetic fields and high pressures, as well as the magnetoresistance measurements, reveal a large critical field, exceeding 19 T at 0.6 K and 2.4 GPa, sharply decreasing receding the superconductivity dome. The previously reported $\it{T-p}$ and $\it{H-T}$ phase diagrams are completed by our high-pressure data and discussed in the frame of previous results., Comment: 16 pages, 5 figures

Here we report a new quasi-one-dimensional $S$ = 1 chain compound NiTe$_{2}$O$_{5}$. From the comprehensive study of the structure and magnetic properties on high quality single crystalline NiTe$_{2}$O$_{5}$, it's revealed that NiTe$_{2}$O$_{5}$ undergoes a transition into an intriguing long-range antiferromagnetic order at $T_{\rm N}=30.5 {\rm K}$, in which longitudinal magnetic moments along the chain direction are ferromagnetically ordered, while their transverse components have an alternating ferromagnetic-antiferromagnetic coupling. Even though the temperature dependence of magnetic susceptibility represents an archetypal anisotropic antiferromagnetic order, we found that critical behavior of unconventional nature with $\alpha'\sim0.25$ and $\beta\sim0.18$ is accompanied by the temperature evolution of the antiferromagnetic order parameter.

The results of a single-crystal X-ray-diffraction study of the evolution of crystal structures of VI3 with temperature with emphasis on phase transitions are presented. Some related specific-heat and magnetization data are included. The existence of the room-temperature trigonal crystal structure R-3 (148) has been confirmed. Upon cooling, VI3 undergoes a structural phase transition to a monoclinic phase at Ts ~ 79 K. Ts is reduced in magnetic fields applied along the trigonal c-axis. When VI3 becomes ferromagnetic at TFM1 ~ 50 K, magnetostriction-induced changes of the monoclinic-structure parameters are observed. Upon further cooling, the monoclinic structure transforms into a triclinic variant at 32 K which is most likely occurring in conjunction with the previously reported transformation of the ferromagnetic structure. The observed phenomena are preliminarily attributed to strong magnetoelastic interactions.

We present the results of the high-temperature neutron and x-ray diffraction experiments on the Ca3-xSrxTi2O7 (x = 0.5, 0.8, 0.85, 0.9) compounds. The ferro- to paraelectric transition in these hybrid improper ferroelectric materials arises from the so-called trilinear coupling. Depending on the Strontium content, various structures and phase transitions, different from theoretical predictions, emerge. The in-situ x-ray powder diffraction indicates a direct ferro- to paraelectric transition between the orthorhombic A21am and tetragonal undistorted I4/mmm phase for x < 0.6. We identified a reduction in the trilinear coupling robustness by increasing the Sr-doping level to lead to the emergence of the intermediate tetragonal P42/mnm phase and the gradual suppression of the orthorhombic phase. The observed character of the structure transitions and the Ca3-xSrxTi2O7 phase diagram are discussed in the framework of theoretical models of other related hybrid improper ferroelectric systems., Comment: 10 pages, 3 figures, 1 table

New frustrated antiferromagnetic compounds CuRE2Ge2O8 (RE=Pr, Nd, Sm, Eu) have been investigated using high-resolution x-ray diffraction, magnetic and heat capacity measurements. These systems show different magnetic lattices depending on rare-earth element. The nonmagnetic Eu compound is a S=1/2 two-dimensional triangular antiferromagnetic lattice oriented in the ac plane with geometrical frustration. On the other hand, the Pr, Nd, and Sm compounds show a three-dimensional honeycomb-tunnel-like lattice made of RE^3+ running along the a axis with the characteristic behavior of frustrated antiferromagnets., Comment: 9 pages, 5 figures

A prototypical quasi-2D metallic compound, 1T-TaS_2 has been extensively studied due to an intricate interplay between a Mott-insulating ground state and a charge density-wave (CDW) order. In the low-temperature phase, 12 out of 13 Ta_{4+} 5\textit{d}-electrons form molecular orbitals in hexagonal star-of-David patterns, leaving one 5\textit{d}-electron with \textit{S} = 1/2 spin free. This orphan quantum spin with a large spin-orbit interaction is expected to form a highly correlated phase of its own. And it is most likely that they will form some kind of a short-range order out of a strongly spin-orbit coupled Hilbert space. In order to investigate the low-temperature magnetic properties, we performed a series of measurements including neutron scattering and muon experiments. The obtained data clearly indicate the presence of the short-ranged phase and put the upper bound on ~ 0.4 \textit{\mu}_B for the size of the magnetic moment, consistent with the orphan-spin scenario., Comment: 11 pages, 4 figures + supplemental material. Accepted by npj Quantum Materials

We found new two-dimensional (2D) quantum (S=1/2) antiferromagnetic systems: CuRE2Ge2O8 (RE=Y and La). According to our analysis of high-resolution X-ray and neutron diffraction experiments, the Cu-network of CuRE2Ge2O8 (RE=Y and La) exhibits a 2D triangular lattice linked via weak bonds along the perpendicular b-axis. Our bulk characterizations from 0.08 to 400 K show that they undergo a long-range order at 0.51(1) and 1.09(4) K for the Y and La systems, respectively. Interestingly, they also exhibit field induced phase transitions. For theoretical understanding, we carried out the density functional theory (DFT) band calculations to find that they are typical charge-transfer-type insulators with a gap of Eg = 2 eV. Taken together, our observations make CuRE2Ge2O8 (RE=Y and La) additional examples of low-dimensional quantum spin triangular antiferromagnets with the low-temperature magnetic ordering., Comment: 15 pages, 6 figures, and 1 table

The properties of the novel heavy fermion superconductor Ce$_3$PtIn$_{11}$ are investigated by thermodynamic and transport measurements at ambient and under hydrostatic pressure. At ambient pressure the compound exhibits two successive magnetic transitions at $T_1$ $\approx$ 2.2 K and $T_{\rm N}$ $\approx$ 2 K into antiferromagnetically ordered states and enters into a heavy fermion superconducting phase below $T_{\rm c}$ $\approx$ 0.32 K. The coexistence of long-range magnetic order and superconductivity is discussed in the context of the existence of the two crystallographically inequivalent Ce-sites in the unit cell of Ce$_3$PtIn$_{11}$. The experimental data allow us to construct the pressure-temperature phase diagram., Comment: accepted to PRB

The evolution of magnetism and superconductivity in Ce$_2$Rh$_{1-x}$Pd$_x$In$_8$ solid solutions has been studied within the entire concentration range by means of thermodynamic and magnetic measurements at ambient pressure and at temperatures between 0.35 K and room temperature. For this purpose, single crystals with Pd concentrations x = 0, 0.10, 0.15, 0.30, 0.45, 0.55, 0.85 and 1 have been grown from In self-flux and characterized by x-ray diffraction and microprobe analysis. Starting from the antiferromagnet Ce$_2$RhIn$_8$, the N\'eel temperature gradually decreases with increasing Pd concentration and the antiferromagnetism has disappeared for $x \ge 0.45$. Superconductivity has been observed only for Ce$_2$PdIn$_8$.

The effect of substituting Rh in CeRh1-xPdxIn5 with Pd up to x = 0.25 has been studied on single crystals. The crystals have been grown by means of the In self-flux method and characterized by x-ray diffraction and microprobe. The tetragonal HoCoGa5-type of structure and the c/a ratio of the parent compound remains intact by the Pd substitution; the unit cell volume increases by 0.6 % with x = 0.25 of Pd. The low-temperature behavior of resistivity was studied also under hydrostatic pressure up to 2.25 GPa. The Pd substitution for Rh affects the magnetic behavior and the maximum value of the superconducting transition temperature measured at pressures above 2 GPa only negligibly. On the other hand, the results provide evidence that superconductivity in CeRh0.75Pd0.25In5 is induced at significantly lower pressures, i.e. the Pd substitution for Rh shifts the CeRh1-xPdxIn5 system closer to coexistence of magnetism and superconductivity at ambient pressure., Comment: 15 pages, 8 figures, 2 tables; accepted for publication in Journal of Physics: Condensed Matter

We report on the single crystal properties of the novel U$_{2}$RhIn$_{8}$ compound studied in the context of parent URhIn$_{5}$ and UIn$_{3}$ systems. The compounds were prepared by In self-flux method. U$_{2}$RhIn$_{8}$ adopts the Ho$_{2}$CoGa$_{8}$-type structure with lattice parameters a $= 4.6056(6)$ \AA\ and c $= 11.9911(15)$ \AA. The behavior of U$_{2}$RhIn$_{8}$ strongly resembles that of the related URhIn$_{5}$ and UIn$_{3}$ with respect to magnetization, specific heat and resistivity except for magnetocrystalline anisotropy developing with lowering dimensionality in the series UIn$_{3}$ vs. U$_{2}$RhIn$_{8}$ and URhIn$_{5}$. U$_{2}$RhIn$_{8}$ orders antiferromagnetically below T$_{\textrm{N}}$ $= 117$ K and exhibits a slightly enhanced Sommerfeld coefficient $\gamma = 47$ mJ$\cdot$mol$^{-1}\cdot$K$^{-2}$. Magnetic field leaves the value of N\'{e}el temperature for both URhIn$_{5}$ and U$_{2}$RhIn$_{8}$ unaffected up to 9 T. On the other hand, T$_{\textrm{N}}$ is increasing with applying hydrostatic pressure up to 3.2 GPa. The weak temperature dependence of $\chi(T)$ in all studied compounds might be attributed to the mainly itinerant nature of 5f electrons. The character of uranium 5f electron states of U$_{2}$RhIn$_{8}$ was studied by first principles calculations based on the density functional theory. The overall phase diagram of U$_{2}$RhIn$_{8}$ is discussed in the context of magnetism in the related URhX$_{5}$ and UX$_{3}$ (X = In, Ga) compounds.

We report on synthesis and anisotropic physical properties of URhIn$_{5}$. High quality single crystals were grown in In-flux. The compound undergoes a second order phase transition into an antiferromagnetic state at T$_{\textrm{N}}$ = 98 K. The transition is field independent up to 9 T. An increase of the resistivity $\rho$ with j along the [100], [110] and [001] tetragonal axis indicates a spin-density-wave induced order with the gap opening first along the [001] direction. The magnetic susceptibility $\chi$ = M/H exhibits a strong anisotropy. Above T $=$ 200 K, $\chi$(T) follows Curie-Weiss law with the effective moment of $\mu_{\textrm{eff}}$ = 3.71 $\mu_{\textrm{B}}/$U and the Weiss temperatures of $\theta_{\textrm{P}}^{[100]} = -900$ K and $\theta_{\textrm{P}}^{[001]} = -500$ K for H $\parallel$ [100] and H $\parallel$ [001] respectively. The characteristic Kondo-like temperature for URhIn$_{5}$ yields T$_{\textrm{K}} =$ 125 K.

The magnetic phase diagram of the tetragonal Ho$_2$RhIn$_8$ compound has similar features to many related systems, revealing a zero magnetic field AF1 and a field-induced AF2 phases. Details of the magnetic order in the AF2 phase were not reported yet for any of the related compounds. In addition, only the Ho$_2$RhIn$_8$ phase diagram contains a small region of the incommensurate zero-field AF3 phase. We have performed a number of neutron diffraction experiments on single crystals of Ho$_2$RhIn$_8$ using several diffractometers including experiments in both horizontal and vertical magnetic fields up to 4 T. We present details of the magnetic structures in all magnetic phases of the rich phase diagram of Ho$_2$RhIn$_8$. The Ho magnetic moments point along the tetragonal $c$ axis in every phase. The ground-state AF1 phase is characterized by propagation vector $\textbf{k}$ = (1/2, 0, 0). The more complex ferrimagnetic AF2 phase is described by four propagation vectors $\textbf{k}_{0}$ = (0, 0, 0), $\textbf{k}_{1}$ = (1/2, 0, 0), $\textbf{k}_{2}$ = (0, 1/2, 1/2), $\textbf{k}_{3}$ = (1/2, 1/2, 1/2). The magnetic structure in the AF3 phase is incommensurate with $\textbf{k}_{AF3}$ = (0.5, $\delta$, 0). Our results are consistent with theoretical calculations based on crystal field theory., Comment: submitted to PRB

We report on single crystal growth and crystallographic parameters results of Ce$_2$PdIn$_8$, Ce$_3$PdIn$_{11}$, Ce$_2$PtIn$_8$ and Ce$_3$PtIn$_{11}$. The Pt-systems Ce$_2$PtIn$_8$ and Ce$_3$PtIn$_{11}$ are synthesized for the first time. All these compounds are member of the Ce$_n$T$_m$In$_{3n+2m}$ (n = 1, 2,..; m = 1, 2,.. and T = transition metal) to which the extensively studied heavy fermion superconductor CeCoIn$_5$ belongs. Single crystals have been grown by In self-flux method. Differential scanning calorimetry studies were used to derive optimal growth conditions. Evidently, the maximum growth conditions for these materials should not exceed 750 $^{\circ}$C. Single crystal x-ray data show that Ce$_2$TIn$_8$ compounds crystallize in the tetragonal Ho$_2$CoGa$_8$ phase (space group P4/mmm) with lattice parameters a =4.6898(3) $\AA$ and c =12.1490(8) $\AA$ for the Pt-based one (Pd: a = 4.6881(4) $\AA$ and c = 12.2031(8) \AA). The Ce$_3$TIn$_{11}$ compounds adopt the Ce$_3$PdIn$_{11}$ structure with a = 4.6874(4) $\AA$ and c = 16.8422(12) $\AA$ for the Pt-based one (Pd: a = 4.6896 $\AA$ and c = 16.891 \AA). Specific heat experiments on Ce$_3$PtIn$_{11}$ and Ce$_3$PdIn$_{11}$ have revealed that both compounds undergo two successive magnetic transitions at T$_1$ ~ 2.2 K followed by T$_N$ ~ 2.0 K and T$_1$ ~ 1.7 K and T$_N$ ~ 1.5 K, respectively. Additionally, both compounds exhibit enhanced Sommerfeld coefficients yielding {\gamma}$_{Pt}$ = 0.300 J/mol K$^2$ Ce ({\gamma}$_{Pd}$ = 0.290 J/mol K$^2$ Ce), hence qualifying them as heavy fermion materials.

R2RhIn8 compounds (space group P4/mmm, R is a rare-earth element) belong to a large group of structurally related tetragonal materials which involves several heavy-fermion superconductors based on Ce. We have succeeded to grow single crystals of compounds with Nd, Dy and Er and following our previous bulk measurements, we performed neutron-diffraction studies to determine their magnetic structures. The Laue diffraction experiment showed that the antiferromagnetic order below the N\'eel temperature is in all three compounds characterized by the propagation vector k = (1/2, 1/2, 1/2). The amplitude and direction of the magnetic moments, as well as the invariance symmetry of the magnetic structure, were determined by subsequent experiments using two- and four-circle diffractometers. The critical exponents were determined from the temperature dependence of the intensities below TN., Comment: 10 pages, 7 figures, submitted to PRB