Crystal structure of KMnPO4F with short- and long-range order inside the layered magnetic system.

Potassium manganese fluoride phosphate, KMnPO4F, has been obtained through mild hydrothermal synthesis and characterized by scanning electron microscopy, microprobe analysis and X-ray diffraction. The compound possesses an orthorhombic symmetry and chiral space group P212121 with a = 4.7884(2), b = 9.0172(4), c = 9.5801(4) Å, and Z = 4. Its crystal structure is composed of Mn3+O4F square pyramids sharing vertices with PO4 tetrahedra. This anionic framework is neutralized by K+ cations. As the temperature decreases, a short-range correlation state (Tmax ∼ 35 K) of KMnPO4F is formed, followed by the establishment of antiferromagnetic (AFM) long-range order at TN = 25 K. The latter is marked by sharp λ-type anomalies in both Fisher's specific heat d(χ‖T)/dT and heat capacity Cp. Pulsed magnetic field measurements on the single crystals identify the a axis as the easy magnetic axis and reveal a spin-flop transition at µ0Hspin-flop = 19 T. Density functional theory indicates that in variance with the three-dimensional network of KMnPO4F, it is a two-dimensional Ising magnetic system represented by buckled layers of integer spins S = 2 of Mn3+ ions. The strongest AFM exchange interaction, J1 ∼ -13 K, couples Mn3+ ions into linear chains running along the a axis. The chains themselves are ferromagnetically connected (J3 ∼ -4 K) within the ab plane. The interplane AFM exchange interaction (J2 ∼ -1 K) is weak and frustrated.

Preparation and Properties of a High-Entropy Wolframite-Type Antiferromagnet, (Mn0.2Co0.2Ni0.2Cu0.2Cd0.2)WO4.

The homogeneous high-entropy wolframite-type solid solution (Mn1/5Co1/5Ni1/5Cu1/5Cd1/5)WO4 was prepared by solid-state reaction at 1000 °C. Elongated "crystals" were grown from the Na2WO4 flux, but their strongly broadened powder X-ray diffraction patterns indicated partial dissolution. Nevertheless, successive annealing of the homogeneous solid solution for 3-4 h at 800, 700, and 600 °C did not bring any sign of dissolution. Thus, the material is kinetically stable at low temperatures although thermodynamically unstable. The long-range antiferromagnetic order was established at TN ∼ 24.8 K. Based on magnetization and specific heat measurements, a magnetic phase diagram was built, demonstrating the presence of an additional field-induced phase. In contrast to the parent MnWO4, no dielectric anomaly has been found down to 2 K.

Spin-Cluster Glassy and Long-Range Ordered Magnetic States in Honeycomb-Layered Compositionally Complex Oxides Na3-xLixT2SbO6 (T = Cu1/3Ni1/3Co1/3).

The concept of high-entropy oxides has triggered extensive research of this novel class of materials because their numerous functional properties are usually not mere linear combinations of those of the components. Here, we introduce the new series of compositionally complex honeycomb-layered magnets Na3-xLixT2SbO6 (T = Cu1/3Ni1/3Co1/3). An unusual feature of the system is its nonmonotonous dependences of the monoclinic lattice parameters b and ß on x. Rietveld refinement of the crystal structures of the Na and Li end members reveals apparent Sb-T site inversion in the former and considerable Li-Cu site inversion in the latter. The materials are characterized by measurements of specific heat Cp, magnetization M, and ac and dc magnetic susceptibility χ. Na3T2SbO6 exhibits sharp long-range antiferromagnetic order (TN = 10.2 K) preceded by noticeable correlation effects at elevated temperatures. The magnetic phase diagram of Na3T2SbO6 is established. Introduction of Li, just at x = 0.8, destroys AFM order, resulting in spin-cluster glass behavior attributed to Li/Cu inversion, with TG growing with x to 10.4 K at x = 3.

Sequence of Structural and Magnetic Phase Transitions in (NO)Mn6(NO3)13.

New nitrosonium manganese(II) nitrate, (NO)Mn6(NO3)13, has been synthesized and structurally characterized. In the temperature range of 45-298 K, the crystal is hexagonal (centrosymmetric sp. gr. P63/m). Mn2+ ions are assembled into tubes along axis c with both NO3- filling and coating. The nitrosonium cation is located in the framework cavity and is disordered by a 3-fold axis. At the temperature TS1 = 190 K, a structural phase transition related to the libration of the intertube NO3 group and a small variation of Mn polyhedron is observed. Moreover, the anomalies in physical properties of (NO)Mn6(NO3)13 allow suggesting that ordering of NO+ units occurs at low temperatures. The antiferromagnetic ordering in this compound is preceded by the formation of a short-range correlation regime at about 25 K and takes place in two steps at TN1 = 12.0 K and TN2 = 8.4 K.

Lamellar Crystal Structure and Haldane Magnetism in NH4 VPO4 OH.

A novel vanadium hydroxide-phosphate, NH4 VPO4 OH, was synthesized hydrothermally in V2 O5 -NH4 H2 PO4 -citric acid system at 230 °C. It was characterized by XRD, TG-DSC, SEM-EDX, FTIR and NMR spectroscopy. NH4 VPO4 OH is isostructural with NH4 GaPO4 OH and features edge-sharing chains of VO6 octahedra. These chains running along [010] direction of the unit cell are connected by phosphate tetrahedra to form infinite layers parallel to the (100) plane. Ammonium cations are embedded between the heteropolyhedral layers. According to the thermodynamic and NMR measurements supported by the first-principles calculations, NH4 VPO4 OH presents a rare case of Haldane spin system with spin S=1 based on V3+ ions.

Thermodynamic Properties and DFT Study on Highly Frustrated Cr3BO6: Coexistence of Spin-Singlets with Long-Range Magnetic Order.

The triangle-based magnetic subsystem of borates with the mineral norbergite structure M3BO6 (M = Fe, Cr, V) makes these compounds unique to investigate rare quantum ground states influenced by strong magnetic frustration. In this work, we investigated the thermal and magnetic properties of Cr3BO6 to find that despite very large negative Weiss temperature Θ = -160.7 K, it orders only at TN = 4.5 K and experiences a spin-flop transition at µ0H = 5 T. Density functional theory (DFT) calculations of exchange interaction parameters allow for suggesting the model of magnetic subsystem in chromium borate Cr3BO6. The results prove the decisive role of magnetic frustration on the formation of long-range order, providing therefore a basis for future study. Both experimental data and first-principles calculations point to the coexistence of chromium spin-singlets with long-range antiferromagnetic order.

Synthesis and Characterization of Molybdenum- and Sulfur-Doped FeSe.

During the past decade, two-dimensional (2D) layered materials opened novel opportunities for the exploration of exciting new physics and devices owing to their physical and electronic properties. Among 2D materials, iron selenide has attracted much attention from several physicists as they provide a fruitful stage for developing new superconductors. Chemical doping offers a powerful approach to manipulate and optimize the electronic structure and physical properties of materials. Here, to reveal how doping affects the physical properties in FeSe, we report on complementary measurements of molybdenum- and sulfur-doped FeSe with theoretical calculations. Mo0.1Fe0.9Se0.9S0.1 was synthesized by a one-step solid-state reaction method. Crystal structure and morphology were studied using powder X-ray diffraction and scanning electron microscopy. Thermal stability and decomposition behavior in doped samples were studied by thermogravimetric analysis, and to understand the microscopic influence of doping, we performed Raman spectroscopy. First-principles calculations of the electronic structure illustrate distinct changes of electronic structures of the substituted FeSe systems, which can be responsible for their superconducting properties.

K2Mn3O(OH)(VO4)(V2O7) with Sawtooth Chains of Multivalent Manganese Triangular Trimer Units: Magnetic Susceptibility Shrouding a Long-Range Antiferromagnetic Order of Ferromagnetic Triangles.

ortho-Pyrovanadate (or ortho-diorthovanadate) K2Mn23+Mn2+O(OH)(VO4)(V2O7) synthesized hydrothermally crystallizes in the orthorhombic space group Pnma with a = 17.9155(5), b = 5.8940(2), c = 10.9971(3) Å, V = 1161.23(6) Å3, and Z = 4. Its crystal structure features linear chains of edge-sharing Mn3+O6 octahedra with every second pair of Mn3+O6 octahedra condensed with a Mn2+O6 octahedron on one side of a chain in a sawtooth pattern so that each sawtooth chain consists of a triangular trimer. These sawtooth chains, running parallel to the b axis and linked by the VO4 and V2O7 groups, form a framework with channels populated by K atoms. The new compound is a structural analogue of the mineral zoisite Ca2Al3O(OH)(SiO4)(Si2O7), showing a striking example of very different chemical compositions. K2Mn3O(OH)(VO4)(V2O7) undergoes a phase transition into an ordered antiferromagnetic (AFM) state at TN = 14.4 K, which was detected by high-frequency electron spin resonance as well as by both specific heat Cp and Fisher's specific heat d(χT)/dT measurements. However, this phase transition was not detected by magnetic susceptibility measurements. The origin of this puzzling observation was resolved by evaluating the spin exchanges of K2Mn3O(OH)(VO4)(V2O7), which revealed that each triangular trimer is a ferromagnetically coupled cluster, and the observed ordering involves an AFM ordering between the ferromagnetic (FM) clusters. This ordering is shrouded in magnetic susceptibility measurements due to the susceptibility contributions from the individual FM triangular trimers even below TN. We showed that the magnetic susceptibility of K2Mn3O(OH)(VO4)(V2O7) between ∼30 K and room temperature is satisfactorily described by an AFM chain made up of ferromagnetically coupled triangular clusters, as described by a few spin-exchange parameters.

Successive short- and long-range magnetic ordering in rosiaite-type CoGeTeO6 prepared by ion-exchange reaction.

The missing member of the rosiaite family, CoGeTeO6, was synthesized by mild ion-exchange reactions and characterized by magnetization M and specific heat Cp measurements. It exhibits a successive short- and long-range magnetic ordering at Tshort-range ≈ 45 K and TN = 15 K, respectively. Based on these measurements, the magnetic H-T phase diagram was established, showing two antiferromagnetic phases separated by a spin-flop transition. The reason why the pronounced short-range correlation occurs at a temperature nearly three times higher than TN was found by evaluating the Co-O⋯O-Co exchange interactions using energy-mapping analysis. Although CoGeTeO6 has a layered structure, its magnetic structure consists of three-dimensional antiferromagnetic lattices made up of rhombic boxes of Co2+ ions. The experimental data obtained at high temperatures agree well with the computational results by treating the Co2+ ions of CoGeTeO6 as S = 3/2 ions, but the heat capacity and magnetization data were obtained at low temperatures by treating the Co2+ ion as a Jeff = 1/2 ion.

Anhydrous copper tellurite disulfate Cu3TeO3(SO4)2 featuring the coexistence of spin singlets and a long-range antiferromagnetic order.

Anhydrous copper tellurite sulfate, Cu3TeO3(SO4)2, has been synthesized via vapor transport reactions in sealed silica glass ampoules. In measurements of magnetization M, magnetic susceptibility χ, specific heat Cp and X-band electron spin resonance, a long-range antiferromagnetic order at TN = 13 K and an H-T magnetic phase diagram have been established. One-third of Cu2+ ions were found to form magnetically silent dimers. A peak in dielectric permittivity ε, which accompanies the Néel order, allows considering Cu3TeO3(SO4)2 as a magnetoelectric multiferroic material of the second type. Density functional theory calculations provided estimations of leading exchange interaction parameters.

Correction to Stable Sulfuric Vapor Transport and Liquid-Sulfur Growth on Transition Metal Dichalcogenides.

[This corrects the article DOI: 10.1021/acs.cgd.2c01318.].

New Nabokoite-like Phases ACu7 TeO4 (SO4 )5 Cl (A=Na, K, Rb, Cs) with Decorated and Distorted Square Kagome Lattices.

A new family of compounds ACu7 TeO4 (SO4 )5 Cl (A=Na, K, Rb, Cs) isostructural to mineral Nabokoite (K species) was synthesized by solid state and gas transport reactions in sealed ampoules and characterized in measurements of magnetization and specific heat in a wide temperature range. These complex compounds are of the utmost interest as a testing playground to study the properties of quasi-two-dimensional magnets with a square kagome lattice geometry. A quantum ground state of such a corner-sharing network is a spin liquid. Unlike idealized grid analyzed in numerous models, the square kagome lattice in nabokoites is wavy and distorted being composed of versatile triangles. Moreover, it contains "excessive" decorating magnetic ions, which makes magnetism of these objects even more complicated. The interaction of these decorating ions through virtual excitations of the square kagome lattice is accompanied by the formation of a long-range magnetic order coexisting with the spin liquid.

Stable Sulfuric Vapor Transport and Liquid Sulfur Growth on Transition Metal Dichalcogenides.

Transition metal dichalcogenides (TMDs) are an emergent class of low-dimensional materials with growing applications in the field of nanoelectronics. However, efficient methods for synthesizing large monocrystals of these systems are still lacking. Here, we describe an efficient synthetic route for a large number of TMDs that were obtained in quartz glass ampoules by sulfuric vapor transport and liquid sulfur. Unlike the sublimation technique, the metal enters the gas phase in the form of molecules, hence containing a greater amount of sulfur than the growing crystal. We have investigated the physical properties for a selection of these crystals and compared them to state-of-the-art findings reported in the literature. The acquired electronic properties features demonstrate the overall high quality of single crystals grown in this work as exemplified by CoS2, ReS2, NbS2, and TaS2. This new approach to synthesize high-quality TMD single crystals can alleviate many material quality concerns and is suitable for emerging electronic devices.

First crystal structure of an Fe(III) anionic complex based on a pyruvic acid thiosemicarbazone ligand with Li+: synthesis, features of magnetic behavior and theoretical analysis.

The iron(III) anionic complex based on a pyruvic acid thiosemicarbazone ligand with the lithium cation Li[FeIII(thpy)2]·3H2O (1) has been synthesized and characterized by FTIR spectroscopy, powder and single crystal X-ray diffraction, direct current magnetic susceptibility measurements, and 57Fe Mössbauer spectroscopy. Moreover, the molecular structure of the [Fe(thpy)2]- anion has been determined for the first time. The [Fe(thpy)2]- units in the triclinic P1̄ lattice of 1 are assembled into layers parallel to the bc plane. The Li+ cations and water molecules are located between the layers and the structure is stabilized by hydrogen bonding. The [Fe(thpy)2]- anions form interconnected dimer pairs through hydrogen bonds and short contacts with Fe⋯Fe separation of 6.7861(4) Å. According to dc magnetic measurements, compound 1 demonstrates an incipient spin-crossover transition from the LS (S = 1/2) to the HS (S = 5/2) state above 250 K. The Bleaney-Bowers equation for a model of an isolated LS dimer with a mean-field correction was applied to fit the experimental data of magnetic susceptibility dependence on temperature in the temperature range of 2-250 K. The intra-dimer J1 = -1.79(1) K and inter-dimer J2 = -0.24(3) K antiferromagnetic coupling constants were defined. The analysis of the 57Fe Mössbauer spectra at 80 K and 296 K confirms the presence of the shortened distances between the iron nuclei. Moreover, the influence of the lithium cation on the stabilization of the LS state was shown for the [Fe(thpy)2]- anion. BS-DFT calculations for the optimized structure of two isolated [Fe(thpy)2]- anions also correctly predict a weak exchange J1(calc) = -0.92 K. DFT calculations revealed the OPBE (GGA-type) functional that correctly predicts the spin-crossover transition for the iron(III) thpy compounds. Besides, the effect of the N2O4, N2S2O2, and N2Se2O2 coordination environments on the energy stabilization of the LS state of iron(III) anionic thpy complexes was noted as well.

Magnetic Phase Diagram of van der Waals Antiferromagnet TbTe3.

Terbium tritelluride, TbTe3, orders antiferromagnetically in three steps at TN1 = 6.7 K, TN2 = 5.7 K, and TN3 = 5.4 K, preceded by a correlation hump in magnetic susceptibility at T* ~8 K. Combining thermodynamic, i.e., specific heat Cp and magnetization M, and transport, i.e., resistance R, measurements we established the boundaries of two commensurate and one charge density wave modulated phases in a magnetic field oriented along principal crystallographic axes. Based on these measurements, the magnetic phase diagrams of TbTe3 at H‖a, H‖b and H‖c were constructed.

Ising-like Magnetism in Quasi-Two-Dimensional Co(NO3)2·2H2O.

The appearance of electrically neutral water molecules in the structure of cobalt dinitrate dihydrate, Co(NO3)2⋅2H2O, drastically changes its magnetic properties as compared to its waterless counterpart, Co(NO3)2. The title compound shows Ising-like behavior reflected in its thermodynamic properties. It experiences long-range antiferromagnetic order at TN = 20.5 K and metamagnetic transition at µ0HC = 0.76 T. First-principles calculations produce the values of leading exchange interactions J1 ~ 10 K and J2 ~ 0.5 K and single-ion anisotropy D ~ 1 K which allows us to consider Co(NO3)2⋅2H2O as a quasi-two-dimensional magnetic system.

Nonstoichiometric Ellenbergerite-Type Phosphates: Hydrothermal Synthesis, Crystal Chemistry, and Magnetic Behavior.

We synthesized single crystals of Na0.55Ni6(OH)3(H0.61PO4)4 (I) and polycrystals of (Na, Ni)0.64Ni5.68(OH)3(H0.67PO4)4 (II) with ellenbergerite-like structures using the hydrothermal method. The phases crystallize in the hexagonal space group P63mc with the following unit cell parameters: a = 12.5342(1) Å, c = 4.9470(1) Å, and V = 673.08(2) Å3 for I; a = 12.4708(2) Å, c = 4.9435(2) Å, and V = 665.82(2) Å3 for II; and Z = 2. Their crystal structures are based on a 3D framework built from NiO6 octahedra and PO4 tetrahedra. The difference between I and II lies in the way the structural channels are filled along the [001] direction. These channels accommodate segments of Na- and (Na, Ni)-centered chains of face-sharing octahedra in the structures I and II, respectively. The magnetic susceptibility χ and the specific heat Cp evidence pronounced low-dimensional magnetic behavior at elevated temperatures and the formation of the weakly ferromagnetic long-range order at TNI = 61 K and TNII = 63 K. Analysis of the χ(T) data within both chain and dimer spin models allows the estimation of the leading exchange interaction parameters in the compounds under study.

Magnetic behavior of the novel pentagonal-bipyramidal erbium(III) complex (Et3NH)[Er(H2DAPS)Cl2]: high-frequency EPR study and crystal-field analysis.

We report the synthesis, crystal structure and magnetic properties of the new heptacoordinated mononuclear erbium(III) complex (Et3NH)[Er(H2DAPS)Cl2] (H4DAPS = 2,6-diacetylpyridine bis-(salicylhydrazone)) (1). The coordination polyhedron around the Er(III) ion features a slightly distorted pentagonal bipyramid formed by the pentagonal N3O2 chelate ring of the H2DAPS ligand in the equatorial plane and two apical chloride ligands. Detailed high-frequency/high-field electron paramagnetic resonance (HF-EPR) studies of 1 result in the precise determination of the crystal field (CF) splitting energies (0, 290 and 460 GHz) and effective g-values of the three lowest Kramers doublets (KDs) of the Er(III) ion. The obtained HF-EPR data are in good agreement with the results from CF analysis for the Er(III) ion based on the simulation of the dc magnetic data of 1. The results from dynamic susceptibility measurements indicate that there is no slow relaxation of magnetisation behaviour. This observation is discussed in terms of the electronic structure of 1 obtained from experimental and theoretical results.

Peculiar Spin-Crossover Behavior in the 2D Polymer K[FeIII(5Cl-thsa)2].

A potassium salt of the N2S2O2-coordination Fe(III) anion K[Fe(5Cl-thsa)2] (1) (5Cl-thsa - 5-chlorosalicylaldehyde thiosemicarbazone) is synthesized and characterized structurally and magnetically over a wide temperature range. Two polymorphs of salt 1 characterized by the common 2D polymer nature and assigned to the same orthorhombic Pbcn space group have been identified. The molecular structure of the minor polymorph of 1 was solved and refined at 100, 250, and 300 K is shown to correspond to the LS configuration. The dominant polymorph of 1 features K+ cations disordered over a few crystallographic sites, while the minor polymorph includes fully ordered K+ cations. The major polymorph exhibits a complete three-step cooperative spin-crossover transition both in the heating and cooling modes: The first step occurs in a temperature range from 2 to 50 K; the second abrupt hysteretic step occurs from 200 to 250 K with T1/2 = 230 K and a 6 K hysteresis loop. The third gradual step occurs from 250 to 440 K. According to 57Fe Mössbauer, XRPD, and EXAFS data, the spin-crossover transition for the dominant polymorph is quite peculiar. Indeed, the increase in the HS concentration by 57% at the second step does not result in the expected significant increase in the iron(III)-ligand bond lengths. In addition, the final step of the spin conversion (ΔγHS = 26%) is associated with a structural phase transition with a symmetry lowering from the orthorhombic (Pbcn) to the monoclinic (P21/n) space group. This nontrivial phenomenon was investigated in detail by applying magnetization measurements, electron spin resonance, 57Fe Mössbauer spectroscopy, and DFT calculations. These results provide a new platform for understanding the multistep spin-crossover character in the Fe(III) thsa-complexes and related compounds.