Short-range Antiferromagnetic Interactions Research Articles

Tunable inversion degree of MnIn2S4 thiospinels prepared by high-pressure synthesis, and its implication in the optical and magnetic properties

Indium thiospinels (AIn2S4, A= transition metals) have attracted significant attention due to their potential for manipulating magnetic and optoelectronic properties through changes in chemical composition. Defined in the cubic space group Fd-3 m (No. 227), the crystal structure consists of a framework of edge-sharing InS6 octahedra (Oh symmetry), with A cations coordinated tetrahedrally (Td symmetry) to sulfur. In this study, we describe a rapid high-pressure synthetic method (3.5 GPa) to prepare MnIn2S4 polycrystalline samples, with tunable degree of inversion (λ) or Mn-In antisite, meaning that some Mn occupy the octahedral sites and some In atoms are located at the tetrahedral positions. We found that λ closely depends on the synthesis temperature. Notably, the refinement of the crystal structure from X-ray diffraction data reveals positive correlations between the inversion degree and different properties such as the band gap, expanding its spectral coverage, and the magnetic behavior, depending on the occupancy rate of the octahedral or tetrahedral sites by the strongly magnetic Mn2+ ions. Whereas the paramagnetic behavior is not affected by the inversion degree, for higher λ values (30%<λ < 38%), achieved at synthesis temperatures as high of 800ºC, the random distribution of Mn2+ ions between Td and Oh sites accounts for a spin-glass state with a clear cusp in the magnetic susceptibility (ac and dc), based on the strong short-range antiferromagnetic interactions.

Magnetic and Electrical Properties of CoRE2W2O10 Ceramic Materials.

Microcrystalline samples of CoRE2W2O10 tungstates (RE = Y, Dy, Ho, Er) were prepared by a high-temperature solid-state reaction and then sintered into a ceramic form for unique properties and potential applications. For this purpose, structural, microscopic, ultraviolet-visible (UV-vis), magnetic, electrical, and thermoelectric measurements were performed. These studies showed a monoclinic structure, paramagnetism, short-range antiferromagnetic interactions in all samples, long-range ferrimagnetic interactions only in CoY2W2O10, poor n-type conductivity of 6.7 × 10-7 S/m at room temperature, strong thermal activation (Ea1 = 0.7 eV) in the intrinsic region, a strong increase in the power factor (S2σ) above 300 K, a Fermi energy (EF) of 0.16 eV, and a Fermi temperature (TF) of 1800 K. The above studies suggest that anion vacancy levels, which act as doubly charged donors, and to a lesser extent, the mixed valence band of cobalt ions (Co2+, Co3+), which are located below the bottom of the conduction band and below the Fermi level, are responsible for electron transport.

Weak ferromagnetism in a diamagnetically diluted sublattice of Fe3+ ions in solid solutions Y2 −x Fe1 +xTaO7 (x = 0 –0.2) with pyrochlore-like structure

A series of layered solid solutions Y2-xFe1+xTaO7 (x = 0–0.2) was synthesized and a structural transition (space group R3¯ ↔ space group P3121) was observed at x = 0.1. In Y2−xFe1+xTaO7, which belongs to both structural types, geometrically frustrated 2D sublattices of kagome-type are formed, in which Fe3+ ions are coupled by short-range antiferromagnetic interactions, and the transition to the spin glass state is observed at Tg ∼ 4.3 K. A phenomenon of weak ferromagnetism has been detected, the cause of which is probably a small tilt of the Fe3+ spins due to the Dzyaloshinskii–Moriya antisymmetric superexchange.

Effect of Ca2+ site substitution on structural, optical, electrical and magnetic properties in Nd3+ and Mn2+-co-doped calcium molybdato-tungstates

Ca 1-3x-y Mn y [] x Nd 2x (MoO 4 ) 1-3x (WO 4 ) 3x molybdato-tungstates (▯ denotes vacant sites) were successfully synthesized by high-temperature solid-state reaction. New materials crystallize in scheelite-type structure within whole homogeneity range of solid solution ( x ≤ 0.2000 and y = 0.0200). Morphological features and particle size distribution were investigated by SEM and laser diffraction methods, respectively. Spectroscopic measurements in the UV–vis range was carried out to determine optical direct band gap ( E g ), Urbach energy ( E U ) and confirmation of structural disorder. Refractive index ( n ) was calculated using four different models. Magnetic studies revealed paramagnetic behavior with long-range ferrimagnetic and short-range antiferromagnetic interactions. New materials showed weak n -type electrical conductivity and thermoelectric power factor (S 2 σ) that strongly depends on Nd 3+ ions content. Dielectric parameters, i.e. relative permittivity (ε r ) and energy loss ( tanδ ) are insignificantly dependent on Nd 3+ ions concentration. These effects were considered in terms of structural defects, thermal activation of charge carriers, and the Maxwell–Wagner polarization.

Short-range magnetic interaction in a monolayer 1T−VSe2 film revealed by element-specific x-ray magnetic circular dichroism

We investigated the intrinsic magnetic properties of the two-dimensional ferromagnetic candidate monolayer $1T\text{\ensuremath{-}}{\mathrm{VSe}}_{2}$ films using x-ray magnetic circular dichroism (XMCD), an element-specific magnetic probe. By performing high-resolution measurements, we succeeded in detecting a clear XMCD signal from the atomically thin $1T\text{\ensuremath{-}}{\mathrm{VSe}}_{2}$ films under an external magnetic field. Through manipulation of the x-ray incidence angle, we were able to disentangle the in-plane and out-of-plane magnetic properties and found a strong magnetic anisotropy. Moreover, magnetic-field- and temperature-dependent XMCD revealed that there is no long-range ferromagnetic ordering even at 6 K, but short-range ferromagnetic and antiferromagnetic interactions between neighboring vanadium ions exist. Such low-temperature magnetic behavior signifies that the monolayer $1T\text{\ensuremath{-}}{\mathrm{VSe}}_{2}$ is on the verge of ferromagnetism, and this fact accounts for the reported ferromagnetism in ${\mathrm{VSe}}_{2}$-based heterostructures.

Spin-glass-like state induced by Mn-doping into a moderate gap layered semiconductor SnSe2

Various types of magnetism can appear in emerging quantum materials such as van der Waals layered ones. Here, we report the successful doping of manganese atoms into a post-transition metal dichalcogenide semiconductor: SnSe2. We synthesized a single crystal Sn1−xMnxSe2 with x = 0.04 by the chemical vapor transport method and characterized it by x-ray diffraction and energy-dispersive x-ray spectroscopy. The magnetic properties indicated a competition between coexisting ferromagnetic and antiferromagnetic interactions, from the temperature dependence of the magnetization, together with magnetic hysteresis loops. This means that magnetic clusters having ferromagnetic interactions within a cluster form and the short-range antiferromagnetic interaction works between the clusters; a spin-glass-like state appears below ∼60 K. Furthermore, we confirmed by ab initio calculations that the ferromagnetic interaction comes from the 3d electrons of the manganese dopant. Our results offer a new material platform to understand and utilize the magnetism in the van der Waals layered materials.

Structural disorder and antiferromagnetism in LaNi1–xPtxO3

We report on the B-site substitution of Pt for Ni in the system LaNi1–xPtxO3. The system can only be synthesized between x ​≤ ​0.50, with LaNiO3 (x ​= ​0.00) and the stoichiometric double perovskite La2NiPtO6 (x ​= ​0.50) as the end members. Higher Pt-contents (x ​> ​0.50) are unachievable due to the preference of Pt to being in oxidation state ​+ ​IV in octahedral coordination. Upon introducing Pt into LaNiO3, a phase transformation from rhombohedral (R-3c) to monoclinic (P21/n) symmetry is observed for 0.075 ​≤ ​x ​≤ ​0.125, where all monoclinic samples are B-site ordered, and Pt show a strong preference for the Pt-site (2c-site) for all compositions (x ​≥ ​0.20). Powder X-ray diffraction analysis reveal disorder of the Pt-distribution in several of the non-equimolar samples (0.20 ​≤ ​x ​≤ ​0.40), which point toward cluster formation with domains of high and low Pt-content within each sample. La2NiPtO6 further show an antiferromagnetic transition at ∼ 40 ​K. A similar transition is observed for all monoclinic samples (x ​≥ ​0.20), however, the transition is less pronounced for lower x. This is explained in terms of the structural disorder, i.e. by the coexistence of antiferromagnetic domains with long range order and paramagnetic domains dominated by short range antiferromagnetic interactions.

Electrical transport properties driven by magnetic competition in hole-doped perovskite Pr1-xBaxMnO3 (0.25 ≤ x ≤ 0.36)

In this work, polycrystalline Pr1-xBaxMnO3 (0.25 ≤ x ≤ 0.36) ceramics were synthesized, and their magnetic and electrical transport properties were systematically studied. All samples show two metal-insulator transitions (MITs) corresponding to the high temperature TMI1 and low temperature TMI2, respectively, besides the non-Griffith phase above the ferromagnetic (FM) transition temperature TC. Combining the results of the transport and magnetic properties, it is found that the FM transition temperature TC coincides with the temperature TMI1, which is linearly related to the A-site ionic radius mismatch variance σ2, indicating the enhancement of FM interactions due to the increase of the degree of B-site ordering of Mn3+/Mn4+ ions. The positive correlation between ferromagnetic insulators (FMI) and magnetic interactions, including the FM and short-range antiferromagnetic (AFM) interactions, is confirmed. It is suggested that the first MIT at TMI1 is attributed to the Mn3+/Mn4+ double exchange interactions and the second MIT at TMI2 is closely related to the suppression of the AFM interactions under the internal FM field induced by the Mn3+/Mn4+ DE interactions. This work provides not only a theoretical understanding on the origin of MIT at low temperature, but also a new way for adjusting the FMI in perovskite manganese oxide Pr1-xBaxMnO3 for application.

Effects of TM-doping on structural, magnetic and transport properties in CaTi0.8TM0.2O3 (TM = Mo, Co, and Mn)

This paper reports the structural, morphological, magnetic, and electrical properties of the CaTi0.8TM0.2O3 (TM = Mo, Co, and Mn) system, which was prepared by the solid-state reaction method. Structural analysis was performed by X-ray diffraction (XRD) and the Rietveld refinement method, revealing that the samples crystallize in an orthorhombic structure of space group Pnma (62). Substitution generated a decrease in the lattice parameters and crystal size. The results obtained by scanning electron microscopy (SEM) show that morphology is appropriate and consistent with the reported up to now. The magnetic measurements, performed in the range of the temperature between 9 and 300 K, showed the presence of the antiferromagnetic ordering in all compounds studied. However, a second magnetic transition in lower temperatures was found in the CaTi0.8Mn0·2O3 compound. The resistivity measurements show a semiconductor type behavior in the measured temperature range 5–300 K. The data analysis showed that the transport mechanism of the polycrystalline samples is well described by the variable-range-Hopping model. The results of magnetic and electrical measurements suggest short-range antiferromagnetic interactions is present in the intermediate temperature regime.

Magnetic and photocatalytic properties of nano-sized sulfur-doped trirutile oxide, CuSb2O6

Sulfur-doped trirutile-structured CuSb2O6 was realized by single-step oxidation of Chalcostibite (CuSbS2) with the hydrogen peroxide solution. Its powder X-ray diffraction pattern confirmed the α-polymorphic form of CuSb2O6, with a crystallite size of 6 nm, corroborating well with tetragonal symmetry observed in lattice fringes and SAED pattern. The TEM-EDS analysis indicated sulfur doping in the sample. The dopant amount quantified using thermogravimetric and XPS analysis. The sulfide doping caused the reduction of some amounts of Cu2+ to Cu+ with a noticeable decrease in the bandgap as compared to undoped β-CuSb2O6. The positive slope in the Williamson-Hall plot of sulfur-doped sample implied tensile strain. The short-range antiferromagnetic interaction of Cu2+ was absent in the magnetic measurements of the sample. Instead, it displayed a paramagnetic behavior down to 2 K. Change in electronic structure coupled with the high surface area of 203 m2/g introduced catalytic property in the sample for the photodegradation of carcinogenic rhodamine 6G (Rh 6G) spanning four cycles consecutively. During these experiments, no alteration of catalyst structure was visible.

Spin dynamics of S=2 triangular and honeycomb lattices

Spin dynamics of $S=2$ triangular and honeycomb lattices realized in ${\mathrm{BaNa}}_{2}\mathrm{Fe}{[{\mathrm{VO}}_{4}]}_{2}$ and ${\mathrm{BaNa}}_{2}{\mathrm{Fe}}_{2/3}{\mathrm{Mg}}_{1/3}{[{\mathrm{VO}}_{4}]}_{2}$, respectively, are investigated by magnetization, heat capacity, and particularly $^{57}\mathrm{Fe}$ M\"ossbauer spectroscopy measurements from which spin fluctuation rates are derived. Slight distortions of the $[{\mathrm{FeO}}_{6}]$ polyhedra from ${D}_{3d}$ symmetry probe the respective anisotropy of the electronic ground state. ${\mathrm{BaNa}}_{2}\mathrm{Fe}{[{\mathrm{VO}}_{4}]}_{2}$ and ${\mathrm{BaNa}}_{2}{\mathrm{Fe}}_{2/3}{\mathrm{Mg}}_{1/3}{[{\mathrm{VO}}_{4}]}_{2}$ reveal magnetic decoupling of the underlying magnetic lattices. Down to the lowest temperature of our experiments (3.3 K) only the triangular lattice exhibits long-range order (${T}_{c}=6.5$ K). The long-range order involves only 2/3 of the Fe sites (static, ${H}_{hf}\ensuremath{\approx}190$ kOe), and 1/3 of the Fe sites fluctuate faster than the observation time window of the M\"ossbauer spectroscopy experiment. For the honeycomb lattice two distinct iron sites alternate. The moments oriented within the plane slow down considerably with ${H}_{hf}\ensuremath{\approx}120$ kOe whereas the moments on Fe sites aligned along the $c$ axis retain a three times larger fluctuation frequency. In both cases the orthogonal moments, obtained from the orientation of the hyperfine fields with respect to the electric field gradient, couple through Dzyaloshinskii-Moriya interaction. Magnetization data for both compounds show signs of ferromagnetic alignment of the reduced moments, $M$(0 kOe) $\ensuremath{\approx}2\phantom{\rule{0.28em}{0ex}}{\ensuremath{\mu}}_{B}$ per Fe. The evaluation of the specific heat data and M\"ossbauer spectra for the ${\mathrm{BaNa}}_{2}\mathrm{Fe}{[{\mathrm{VO}}_{4}]}_{2}$ supports the presence of short-range antiferromagnetic interactions below 50 K and suggests a crossover into competing ferromagnetic exchange below 10 K preceding the emerging long-range order.

Metamagnetism and kinetic arrest in a long-range ferromagnetically ordered multicaloric double perovskite Y2CoMnO6

A systematic magnetic study of the double perovskite oxide Y2CoMnO6 (YCMO) has been performed. A monoclinic P21/n phase of YCMO was synthesized using a sol-gel method. Neutron diffraction (ND) measurements evidence the onset of long-range ferromagnetic (FM) ordering at TC ~ 76 K, which persists down to 5 K. The presence of 25% antisite disorder, estimated from the ND data, leads to the appearance of short-range antiferromagnetic (AFM) interactions. The existence of thermal hysteresis due to competing interactions between FM and AFM phases is observed in the M vs. T measurements. The pinning of magnetic domain walls at the Co/Mn antiphase boundaries results in a metamagnetic-like behavior. The field dependence of thermomagnetic irreversibility and the nature of virgin curves indicate the occurrence of a kinetic arrest phenomenon, which is further verified via cooling and heating of the system in an unequal fields (CHUF) protocol. In full agreement with the ND data, a detailed analysis of critical exponents near the paramagnetic (PM)-FM phase transition also establishes YCMO as a long-range interacting mean-field system. A careful examination of the temperature- and field-dependent magnetic entropy change yields an in-depth understanding of coexisting magnetically ordered and disordered phases in YCMO, leading to a comprehensive magnetic phase diagram of this multifunctional double perovskite system.

Frustrated Magnetism in Triangular Lattice TlYbS2 Crystals Grown via Molten Flux.

The triangular lattice compound TlYbS2 was prepared as large single crystals via a molten flux growth technique using sodium chloride. Anisotropic magnetic susceptibility measurements down to 0.4 K indicate a complete absence of long-range magnetic order. Despite this lack of long-range order, short-range antiferromagnetic interactions are evidenced through broad transitions, suggesting frustrated behavior. Variable magnetic field measurements reveal metamagnetic behavior at temperatures ≤2 K. Complex low temperature field-tunable magnetic behavior, in addition to no observable long-range order down to 0.4 K, suggest that TlYbS2 is a frustrated magnet and a possible quantum spin liquid candidate.

Studies of the 4d and 5d 6H perovskites Ba3BM2O9, B = Ti, Zn, Y; M = Ru, Os, and cubic BaB1/3Ru2/3O3 polymorphs stabilised under high pressure.

The synthesis, structures and magnetism of six mixed 3d-5d oxides Ba3BM2O9 (B = Ti, Y, Zn; M = Ru, Os) are described. When prepared at ambient pressure the six oxides display a 6H type perovskite structure comprised of corner sharing BO6 and face sharing M2O9 motifs. Synchrotron X-ray diffraction reveals a small monoclinic distortion in Ba3ZnRu2O9; the remaining oxides exhibit a hexagonal structure. The magnetic properties are dominated by the M-M interactions across the shared face. Only in the mixed valent (M4+/M5+) Y oxides is evidence of long-range magnetic order found. Application of high pressure/high temperature synthetic methods for the Ru containing oxides changes the structure to the archetypical cubic Pm3[combining macron]m perovskite structure, where the B and Ru cations are disordered on the corner sharing BO6 octahedral sites. The magnetic properties of the cubic oxides are dominated by short range antiferromagnetic interactions, the chemical disorder inhibiting long range ordering.

The frustration of being odd: universal area law violation in local systems

At the core of every frustrated system, one can identify the existence of frustrated rings that are usually interpreted in terms of single–particle physics. We check this point of view through a careful analysis of the entanglement entropy of both models that admit an exact single–particle decomposition of their Hilbert space due to integrability and those for which the latter is supposed to hold only as a low energy approximation. In particular, we study generic spin chains made by an odd number of sites with short-range antiferromagnetic interactions and periodic boundary conditions, thus characterized by a weak, i.e. nonextensive, frustration. While for distances of the order of the correlation length the phenomenology of these chains is similar to that of the non-frustrated cases, we find that correlation functions involving a number of sites scaling like the system size follow different rules. We quantify the long-range correlations through the von Neumann entanglement entropy, finding that indeed it violates the area law, while not diverging with the system size. This behavior is well fitted by a universal law that we derive from the conjectured single–particle picture.

Dielectric and magnetic characteristics of Ca1\u2212xMnxMoO4 (0 \u2264 x \u2264 0.15) nanomaterials

Scheelite-type Ca1−xMnxMoO4 (x = 0.0, 0.01, 0.05, 0.10 and 0.15) nanomaterials were successfully synthesized via a combustion route. Dielectric studies showed a weak n-type electrical conductivity characteristic for insulators and low relative permittivity (εr < 15) decreasing with increasing Mn2+ content. CaMoO4 and Mn2+-doped nanomaterials are chemically compatible with Al and Ag electrodes and promising for low-temperature co-fired ceramic applications. Magnetic studies showed, at room-temperature diamagnetism for pure CaMoO4, the balance between diamagnetism and paramagnetism for Ca1−xMnxMoO4 (x = 0.01) and paramagnetic behaviour when 0.05 ≤ x ≤ 0.15 as well as the short-range antiferromagnetic interactions growing in strength as Mn2+ content increases. The Landé factor fitting procedure showed a spin-only contribution to the magnetic moment. CaMoO4 matrix unexpectedly revealed the residual paramagnetism at low temperatures derived probably from the molybdenum ions having unpaired 4d electrons as well as a paramagnetic-diamagnetic transition at 70 K.

Ferromagnetic phases due to competing short- and long-range interactions in the spin-5/2 and spin-2 Blume–Capel model

We broaden the study of the statistical physics of the spin-S Blume–Capel model with ferromagnetic mean-field interactions J in competition with short-range antiferromagnetic interactions K in a linear chain in the thermodynamic limit. This work is dedicated to the case when S takes the half-integer spin S=5/2 and when S assumes the integer value S=2. In both cases the phase diagrams exhibit new ferromagnetic phases (for certain values of K) enclosed by branches emerging from the first-order frontiers of the pure ferromagnetic model. For finite temperatures the complex topologies were obtained by numerical minimization of the free energy and some results were confirmed by Monte Carlo simulations.

Evolution from Griffiths like phase to non-Griffiths like phase with Y doping in [formula omitted

Detailed analysis of the temperature dependent dc susceptibility data shows the modification from the Griffiths like phase (GP) to non-Griffiths like phase (non-GP) in (La1-xYx)0.7Ca0.3MnO3(x=0,0.3,0.4,0.5,0.6) compounds with x. The existence of non-Griffiths phase is revealed from the upward deviation of the inverse susceptibility (1/χ) versus temperature plot from the Curie-Weiss behavior for the compounds with x⩾0.5. Whereas Griffiths phase is identified from the downturn of 1/χ versus T plot from the Curie-Weiss line in the compounds with x=0.3,0.4. The increased lattice distortion (with x) decreases the M-O-Mn bond angle and at the same time increase the electron-phonon (e-ph) coupling which in turn decreases the ferromagnetic double exchange (DE) interactions and enhances the effective short-range antiferromagnetic superexchange interactions between Mn3+/Mn3+ and Mn4+/Mn4+ ions above the Curie temperature (TC). The enhancement of this short-range antiferromagnetic (SR-AFM) interactions have been attributed to the conversions from GP to non-GP phase. The increased SR-AFM interactions with Y doping has also been substantiated from the magnetocaloric study.

Highly frustrated Bi-Cr-Sb-O pyrochlore with spin-glass transition

The detailed study of magnetic properties, including dc and ac measurements, has been carried out on the Bi-Cr-Sb-O pyrochlore. The region of pyrochlore phase existence was determined and photocatalytic properties have been also studied. We revealed that the Bi-Cr-Sb-O pyrochlore phase occurs along Bi2−xCr1+xSbO7 section within the region x = 0.1–0.4. The Cr3+ ions oxidation state in Bi-Cr-Sb-O pyrochlore was confirmed by XANES spectra. The best Rietveld refinement results for Bi1.8Cr1.2SbO7 composition were achieved for the disordered structure model (space group Fd-3m). According to the magnetic data Bi1.8Cr1.2SbO7 is a highly frustrated pyrochlore with short-range antiferromagnetic exchange interactions between the nearest Cr3+ ions. At Tg = 4 К this compound undergoes spin-glass transition.

Yb3+-doped cadmium molybdato-tungstate single crystal – Its structural, optical, magnetic and transport properties

Single crystal of new cadmium and ytterbium molybdato-tungstate (Cd0.9706⎕0.0098Yb0.0196(MoO4)0.9706(WO4)0.0294, where ⎕ denotes cationic vacancies) has been successfully grown by the Czochralski method in air and under 1 MPa. X-ray crystallographic analysis reveals that the as-grown single crystal belongs to a scheelite-type structure (a = b = 5.15539(12) and c = 11.1919(3) Å, space group I41/a), in which Yb3+ ions do not show long-range order and are randomly distributed in the unit cell, substituting the Cd2+ ones. The as-grown single crystal does not show anisotropy of optical properties, i.e. its direct band gap reaches Eg = 1.76 or 1.75 eV along (100) and (001) crystallographic directions, respectively. The single crystal exhibits paramagnetic state with short-range antiferromagnetic and long-range ferrimagnetic interactions, a magnetization with zero coercivity and, a remanence that is almost a universal function of H/T, characterizing superparamagnetic-like behaviour. Electrical studies of the new ytterbium-doped cadmium molybdato-tungstate single crystal show a relatively small dielectric constant (εr<12), large lossiness of Joule-Lenz type observed at low frequencies as well as nonlinear I-V characteristics of Schottky or Maxwell-Wagner type.