Weiss Temperature Research Articles

Thin film synthesis, structural analysis, and magnetic properties of novel ternary transition metal nitride MnCoN2

Recent high-throughput computational searches have predicted many novel ternary nitride compounds providing new opportunities for materials discovery in underexplored phase spaces. Nevertheless, there are hardly any predictions and/or syntheses that incorporate only transition metals into new ternary nitrides. Here, we report on the synthesis, structure, and properties of MnCoN2, a new ternary nitride material comprising only transition metals and N. We find that crystalline MnCoN2 can be stabilized over its competing binaries, and over a tendency of this system to become amorphous, by controlling growth temperature within a narrow window slightly above ambient condition. We find that single-phase MnCoN2 thin films form in a cation-disordered rocksalt crystal structure. X-ray photoelectron spectroscopy analysis suggests that MnCoN2 is sensitive to oxygen through various oxides and hydroxides binding to cobalt on the surface. X-ray absorption spectroscopy is used to verify that Mn3+ and Co3+ cations exist in an octahedrally coordinated environment, which is distinct from a combination of CoN and MnN binaries and in agreement with the rocksalt-based crystal structure prediction. Magnetic measurements suggest that MnCoN2 has a canted antiferromagnetic ground state below 10 K. We extract a Weiss temperature of θ=−49.7K, highlighting the antiferromagnetic correlations in MnCoN2. Published by the American Physical Society 2024

Fabrication of Textured 0.685(Na0.5Bi0.5)TiO3-0.065BaTiO3-0.25SrTiO3 Electrostrictive Ceramics by Templated Grain Growth Using NaNbO3 Templates and Characterization of Their Electrical Properties

Electrostrictive materials based on (Na0.5Bi0.5)TiO3 are promising lead-free candidates for high-precision actuation applications, yet their properties require further improvement. This study aims to enhance the electromechanical properties of a predominantly electrostrictive composition, 0.685(Na0.5Bi0.5)TiO3-0.065BaTiO3-0.25SrTiO3, by using templated grain growth. Textured ceramics were prepared with 1~9 wt% NaNbO3 templates. A high Lotgering factor of 95% was achieved with 3 wt% templates and sintering at 1200 °C for 12 h. Polarization and strain hysteresis loops confirmed the ergodic nature of the system at room temperature, with unipolar strain significantly improving from 0.09% for untextured ceramics to 0.23% post-texturing. A maximum normalized strain, Smax/Emax (d33*), of 581 pm/V was achieved at an electric field of 4 kV/mm for textured ceramics. Textured ceramics also showed enhanced performance over untextured ceramics at lower electric fields. The electrostrictive coefficient Q33 increased from 0.017 m4C−2 for untextured ceramics to 0.043 m4C−2 for textured ceramics, accompanied by reduced strain hysteresis, making the textured 0.685(Na0.5Bi0.5)TiO3-0.065BaTiO3-0.25SrTiO3 composition suitable for high-precision actuation applications. Dielectric properties measured between −193 °C and 550 °C distinguished the depolarization, Curie–Weiss and Burns temperatures, and activation energies for polar nanoregion transitions and dc conduction. Dispersive dielectric constants were found to observe the “two” law exhibiting a temperature dependence double the value of the Curie–Weiss constant, with shifts of about 10 °C per frequency decade where the non-dispersive THz limit was identified.

Magnetic properties, critical behavior, and magnetocaloric effect of Nd1−xSrxMnO3 (0.2 ≤ x ≤ 0.5): The role of Sr doping concentration

Magnetic characteristics, magnetocaloric effect, and critical behavior of Nd1−xSrxMnO3 compounds by Sr doping (x = 0.2, 0.3, 0.4, 0.5) were studied. All samples maintained orthorhombic structures, but the space group changed from Pnma (No. 62) for x = 0.2, 0.3 to Imma (No. 74) for x = 0.4, 0.5. As Sr doping increased, the Curie temperature (TC), Curie–Weiss temperature (TCW), and magnetization increased, attributed to the double exchange (DE) interaction. A discrepancy between TCW and TC was observed due to the competition between polarons and DE interaction. The critical behavior was investigated systematically using the self-consistent (modified Arrott plots, MAP) method and the Kouvel–Fisher (KF) relation. The KF relation was suitable for the samples with x = 0.2 and 0.5, while the MAP method was suitable for the samples with x = 0.3 and 0.4. Among the Ising, XY, Heisenberg, and mean-field models, the samples with x = 0.2, 0.3, and 0.4 aligned more closely with the mean-field model, except for the x = 0.5 sample. Entropy change (−ΔSM) of Nd1−xSrxMnO3 (0.2 ≤ x ≤ 0.5) increased with the applied field, with the maximum value observed around TC. For the sample with x = 0.3, (−ΔSM) reached 4.315 J/kg K at μ0ΔH = 50 kOe, corresponding to a relative cooling power (RCP) of 280.48 J/kg. Remarkably, the x = 0.4 sample displayed (−ΔSM) of 3.298 J/kg K at μ0ΔH = 50 kOe near room temperature, with the RCP of 283.64 J/kg. These findings underscore the role of Sr doping in tuning the magnetic properties, critical behavior, and magnetocaloric effect of NdMnO3.

The ferromagnetic to antiferromagnetic crossover in chromium-based pyroxenes tuned via the Ge to Si ratio

For the isotropic spin Cr3+-based (S = 3/2) chain-structure pyroxenes, NaCrGe2O6 is a ferromagnet while NaCrSi2O6 is an antiferromagnet, offering a platform for studying one-dimensional (1D) magnetic interactions. Here we describe our characterization of the NaCrGe2-xSixO6 (0 ≤ x ≤ 2) solid solution series, locating the ferromagnetic-to-antiferromagnetic crossover composition at x = 1.40. NaCrGe0.6Si1.4O6 has a close-to-zero Weiss temperature, which we attribute to a balance between the ferromagnetic and antiferromagnetic interactions in this pseudo-1D isotropic spin system.

Gapless dynamic magnetic ground state in the charge-gapped trimer iridate Ba4NbIr3O12

We present an experimental investigation of the magnetic ground state in Ba4NbIr3O12, a fractional valent trimer iridate. X-ray absorption and photoemission spectroscopy show that the Ir valence lies between 3+ and 4+ while Nb is pentavalent. Combined dc/ac magnetization, specific heat, and muon spin rotation/relaxation (µSR) measurements reveal no magnetic phase transition down to 0.05 K. Despite a significant Weiss temperature (ΘW∼−15 to −25 K) indicating antiferromagnetic correlations, a quantum spin-liquid (QSL) phase emerges and persists down to 0.1 K. This state likely arises from geometric frustration in the edge-sharing equilateral triangle Ir network. Our µSR analysis reveals a two-component depolarization, arising from the coexistence of rapidly (90%) and slowly (10%) fluctuating Ir moments. Powder x-ray diffraction and Ir-L3edge x-ray absorption fine structure spectroscopy identify 8–10% Nb/Ir site-exchange, reducing frustration within part of the Ir network, and likely leading to the faster muon spin relaxation, while the structurally ordered Ir ions remain highly geometrically frustrated, giving rise to the rapidly spin-fluctuating QSL ground state. At low temperatures, the magnetic specific heat varies as γT+αT2, indicating gapless spinon excitations, and possible Dirac QSL features with linear spinon dispersion, respectively. Published by the American Physical Society 2024

Synthesis, crystal structure, and magnetic properties of Ni[formula omitted]CrBO[formula omitted]

Ni2CrBO5 has been synthesized and investigated by X-ray diffraction, dc magnetization, and specific heat measurements. The unusual cation distribution has been established: the M1 and M3 sites are occupied by Ni2+ ions, the M2 site is by Cr3＋ ions, and the M4 site is mixed, featuring both Ni2+ and Cr3＋ ions. The magnetic order onsets at TN= 140 K, which is confirmed by a λ-type peak in specific heat, followed by the dome-shaped anomaly of the magnetization at about 30 K. In the magnetically ordered state, a remarkable sequence of temperature-induced magnetization reversal sensitive to the measurement’s regime is observed. Dominant antiferromagnetic interactions are characterized by the Weiss temperature θ= −73 K. The effective magnetic moment of 5.37 μB per formula unit is close to the spin-only one. The effect of the cation distribution on the magnetic properties is discussed.

The nematic susceptibility of the ferroquadrupolar metal TmAg2 measured via the elastocaloric effect

Elastocaloric measurements of the ferroquadrupolar/nematic rare-earth intermetallic TmAg2 are presented. TmAg2 undergoes a cooperative Jahn-Teller-like ferroquadrupolar phase transition at 5K, in which the Tm3+ ion’s local 4f electronic ground state doublet spontaneously splits and develops an electric quadrupole moment which breaks the rotational symmetry of the tetragonal lattice. The elastocaloric effect, which is the temperature change in the sample induced by adiabatic strains the sample experiences, is sensitive to quadrupolar fluctuations in the paranematic phase which couple to the induced strain. We show that elastocaloric measurements of this material reveal a Curie-Weiss like nematic susceptibility with a Weiss temperature of T* ≈ 2.7K, in agreement with previous elastic constant measurements. Furthermore, we establish that a magnetic field along the c-axis acts as an effective transverse field for the quadrupole moments.

Order-to-Disorder Transition and Hydrogen Bonding in the Jahn-Teller Active NH4CrF3 Fluoroperovskite.

Large quantities of high-purity NH4CrF3 have been synthesized using a wet-chemical method, and its structural chemistry and magnetic properties are investigated in detail for the first time. NH4CrF3 is a tetragonal fluoroperovskite that displays an ordering of the ammonium (NH4+) groups at room temperature and C-type orbital ordering. The ammonium groups order and display distinct signs of hydrogen bonds to nearby fluoride anions by buckling the Cr-F-Cr angle away from 180°. The ammonium ordering remains up to 405 K, much higher than in other ammonium fluoroperovskites, indicating a correlation between the flexibility of the Jahn-Teller ion, the hydrogen bond formation, and the ammonium ordering. At 405 K, an order-to-disorder transition occurs, where the ammonium groups disorder, corresponding to a transition to higher symmetry. This is accompanied by a contraction of the unit cell from breaking hydrogen bonds, similar to the phenomenon observed in water ice melting. The compound orders antiferromagnetically with a Neél temperature of 60 K, an effective paramagnetic moment of 4.3 μB, and a Weiss temperature of -33 K. An A-type antiferromagnetic structure is identified by neutron diffraction, with an ordered moment of 3.72(2) μB.

Quantum spin liquid ground state in the trimer rhodate Ba4NbRh3O12

Frustrated magnets offer a plethora of exotic magnetic ground states, including quantum spin liquids (QSLs), in which enhanced quantum fluctuations prevent a long-range magnetic ordering of the strongly correlated spins down to lowest temperature. Here we have investigated the trimer based mixed valence hexagonal rhodate Ba4NbRh3O12 using a combination of dc and ac magnetization, electrical resistivity, specific heat, and muon spin rotation/relaxation (μSR) measurements. Despite the substantial antiferromagnetic exchange interactions, as evident from the Weiss temperature (θW∼−35 to −45K), among the Rh-local moments, neither long-range magnetic ordering nor spin freezing is observed down to at least 50 mK, in ac-susceptibility, specific heat, and zero-field μSR measurements (down to 0.26 K). We ascribe the absence of any magnetic transition to enhanced quantum fluctuations as a result of geometrical frustration arising out of the edge-sharing equilateral Rh-triangular network in the structure. Our longitudinal-field μSR result evidences persistent spin fluctuations down to 0.26 K, thus stabilizing a dynamic QSL ground state in Ba4NbRh3O12. Furthermore, the magnetic specific heat data at low T reveal a significant T-linear contribution plus a quadratic T dependence, which may indicate the gapless Dirac QSL phenomenology of the spinon excitations with a linear dispersion. Published by the American Physical Society 2024

Cryogenic magnetocaloric effects of NaLnF4 (Ln = Gd, Tb, Dy, Ho, Er, Tm, and Yb)

Cryogenic refrigeration technology based on magnetocaloric effects plays a critical role in a variety of technological applications. In this paper, we report the cryogenic magnetocaloric effects of a series of sodium-rare earth fluoride samples (Ln = Gd, Tb, Dy, Ho, Er, Tm, Yb) synthesized by the solid-state reaction method. These compounds all crystallize in a hexagonal crystal structure. Down to 2 K, no magnetic ordering was detected, while all compounds show negative Curie–Weiss temperatures indicative of strong antiferromagnetic coupling. Magnetic fields effectively suppress the magnetic fluctuations, leading to a maximum magnetic entropy change of −56 J kg−1 K−1 in NaGdF4 at the magnetic field change from 0 to 50 kOe. These series of compounds are potentially excellent magnetic refrigerants at low temperatures.

The magnetic and electric transport properties in erbium-doped layered perovskite iridate Sr2–xErxIrO4

The 5d oxide Sr2IrO4 with a layered perovskite structure has been investigated due to its peculiar Jeff = 1/2 insulating ground state. In this research, we investigate the evolution of magnetic and electric transport properties of Er-doped polycrystalline perovskite iridates Sr2–xErxIrO4 (0 ≤ x ≤ 0.06). Er3+ is magnetic and can thus provide magnetic interactions with Ir. Also, Er3+ doping introduces a carrier-doping effect. We find that substituting Sr2+ with Er3+ still preserves the I41/acd crystal structure, while it causes the rotation of IrO6 octahedra φ to decrease. In this case, the Ir–O1–Ir bond angle increases and the tetragonal distortion c/a decreases. The magnetic properties present a suppressed transition temperature, a decreased Curie–Weiss temperature, and an increased effective magnetic moment. The electrical resistivity of the doped samples decreases with doping, which originates from the crystal distortion and electron doping. Theoretical calculations represent an increase in band filling and an improvement in the conduction property with doping.

New heteroleptic l-argininato copper(II) complex with bromide and N, N’– heterocyclic ligands – synthesis, supramolecular, spectroscopic, magnetic and theoretical investigations

A new heteroleptic [CuBr(l−Arg)(bpy)]Br·2H2O (1) (l−Arg=l−Arginine, bpy=2,2’−bipyridine) complex has been synthesized and its molecular and supramolecular structure aspects have been discussed based on the X−ray single crystal structure and Hirshfeld analyses. In addition, the properties of complex 1 have been elucidated using different spectroscopic methods (FT−IR / FIR, Raman, NIR−Vis−UV, Q− / X− band EPR) and magnetic measurements. In this complex, the bromide anion occupies the apex of a slightly distorted square pyramid (τ = 0.12). The [CuBr(l−Arg)(bpy)]+ complex units exhibit a ribbon−like organization, with Cu(II) metal centers located at the corners of triangles where the shortest Cu∙∙∙Cu distance is 5.579 Å. The aromatic moieties of bpy are aligned nearly parallel leading to π···π interactions. Both, non−bonded and coordinated, Br− ions act as hydrogen−bond acceptors for guanidinium groups. Hirshfeld analysis indicated the importance of the Br∙∙∙H (17.9 − 18.4 %), O∙∙∙H (14.9−15.2 %), and H∙∙∙H (42.3−43.1 %) interactions in the molecular packing of the studied complex. Atoms in molecules (AIM) calculations indicated mainly the closed shell character for the Cu−N, Cu−O and Cu−Br coordination interactions. The G value calculated using the Q−band EPR spectra parameters g|| = 2.235 and g⊥= 2.05 is 4.7, what indicating negligible coupling and that local tetragonal axes are aligned parallel. A negative value of Weiss temperature θCW = -0.32 K indicates the presence of weak antiferromagnetic coupling between the neighboring Cu(II) ions mediated through hydrogen bonds and π-π stacking of aromatic moieties of bpy. The value of gav= 2.113 obtained from Q−band EPR spectra is consistent with that corresponding to the Curie constant (C = 0.4138 emu K mol−1), i.e.g = 2.101, and that obtained from the best fitting to the Brillouin function: g = 2.139.

Coordination complexes of reduced organic dye isoviolanthrone with transition metals and lanthanides [Mn(II), Dy(III), Gd(III), Nd(III)

The reduction of a vat dye isoviolanthrone to the dianion state in the presence of metal-containing compounds yields binuclear coordination complexes. Two manganese(II) acetylacetonate units coordinate to isoviolanthrone2− (L) in {(K+)cryptand}2{[MnII(acac)2]2⋅L}2– (1) with an average Mn–O bond length of 2.022(2) Å. Dysprosium(III)- or gadolinium(III)-2,2,6,6-tetramethyl-3,5-heptanedionate (TMHD) units form {(K+)cryptand}2{[MIII(TMHD)3]2⋅L}2− (M = DyIII for 2 and GdIII for 3) with the length of the M−O bonds of 2.193(3) and 2.254(4) Å, respectively. Tris(cyclopentadienyl)neodymium(III) forms {(Cs+)cryptand}2{[Cp3NdIII]2⋅L}2–⋅C6H4Cl2 (4) with the Nd–O bonds of 2.264(2) and 2.308(2) Å length. The formation of isoviolanthrone2− is supported by their optical spectra, disappearance of the bands of the CO vibrations in the IR-spectra as well as elongation of the CO bonds in 1–4. High-spin (S = 5/2) MnII atoms in 1 have exchange interaction of J = − 0.122 cm−1 at g = 1.98. Lanthanides have weaker coupling through isoviolanthrone2− in 2 and 3 with J = − 0.029 and D = − 0.004 cm−1 for DyIII and J = 0.0019 cm−1 for GdIII. Complex 4 with two Cp3NdIII species demonstrates the χMT value of 2.33 emu⋅K/mol at 300 K, and this value is lower than the theoretically calculated value of 3.39 emu⋅K/mol. The decrease of χMT is observed in the whole 300–1.9 K range providing negative Weiss temperatures of –32 K. That is explained by magnetic behavior of Cp3NdIII similar to pristine Cp3NdIII. Complexes comprising MnII, GdIII, and NdIII show electron paramagnetic resonance (EPR) signals. Zero-field splitting (ZFS) is observed from MnII and GdIII allowing the estimation of zero-field splitting parameter D as − 0.047 and E close to 0 cm−1 for 1 and − 0.033 and − 0.020 cm−1 for 3. Complex 4 with NdIII manifests an asymmetric two-component EPR signal without ZFS. Weak antiferromagnetic couplings are explained by diamagnetism of isoviolanthrone2− and rather long distances between the metal centers of 15.47–16.25 Å. This study shows that the dianions of organic dyes are promising bidentate ligands for preparation of coordination complexes with d- and f-block metal ions.

Structural and magnetic studies of the frustrated S = 1 kagome magnet NH4Ni2Mo2O10H3

The strong geometric frustration of the kagome antiferromagnets (KAFMs) can destabilise conventional magnetic order and lead to exotic electronic states, such as the quantum spin-liquid state observed in some S=12 KAFM materials. However, the ground state of S = 1 KAFM systems are less well understood. Spin nematic phases and valence bond solid ground states have been predicted to form but a paucity of experimental realisations restricts understanding. Here, the S = 1 KAFM NH4Ni2Mo2O10H3 is presented, which has the 3-fold symmetry of the kagome lattice but significant site depletion, with ∼64% site occupancy. Frustration and a competition between exchange interactions are evidenced through the suppression of order below the Weiss temperature |θW| and observation of ferromagnetic and antiferromagnetic characteristics in the magnetisation data. A semi spin glass ground state is predicted based on the ac-field frequency dependence of the magnetic transition and ferromagnetic signal.

Magnetic anisotropy, magnetization reversal and switching in Ni4Nb2O9 single crystals

Ni4Nb2O9 is an insulating compensated ferrimagnet with TN = 77 K and T comp= 33 K. We report here the study of the magnetic anisotropy using millimeter-size crystals grown in an image furnace. The magnetization measurements, vs temperature, performed with H aligned along the three main crystallographic axes, show similar Curie–Weiss temperatures (Θp ≈ 190 K) and rather similar effective paramagnetic moments (from 3.5 μ B to 3.6 μ B). This suggests that the strongest magnetic interaction is the antiferromagnetic one, coupling the ferromagnetic distorted honeycomb layers and zigzag ribbons via face sharing NiO6 octahedra. This strong antiferromagnetic coupling is supported by DFT calculations that do not evidence any inter site ferromagnetic interaction, leading to total compensation between magnetic moments of both Ni2+ sites. Measurements vs magnetic field below TN reveal an anisotropic behaviour, with square magnetization loops for H in the ab plane, whereas linear M(H) curves without hysteresis are observed for H‖c. This anisotropy between ab plane and c axis occurs also in the magnetization reversal (MR), which is observed in the ab plane only. Starting from M(H) virgin curves collected just below T comp= 33 K with H‖a or H‖b, the memory-like effect was tested through magnetization switching induced by H or T alternating changes. Below T comp, smaller H is needed to switch M symmetrically for H along b than along a, and, for T switching (2 K interval, constant H), a larger M change is obtained along a than along b. The comparison with ferrimagnetic oxides which exhibit MR, like spinels or rare earth orthoferrites, shows that Ni4Nb2O9 is unique since only one magnetic cation over two sites in octahedral coordination is at play, thus providing a unique platform to study M switching but also a challenge for theoretical interpretation.

Phase transitions in ferroelectric ZrO2 thin films

In this work, the formation of the orthorhombic phase of ZrO2 together with the minor monoclinic phase were elucidated by X-ray diffraction and transmission electron microscopy. Moreover, oxidized W can be responsible for the formation of oxygen vacancies in the ZrO2 through oxygen scavenging. The ferroelectric properties of the W/ZrO2/W film capacitors were investigated through piezoresponse force microscopy (PFM) and polarization-voltage measurements.A second-order phase transition from the polar orthorhombic phase to the non-polar tetragonal phase was observed. Density functional theory calculations confirm our experimental results and propose that oxygen vacancies are responsible for the Curie–Weiss temperature of 130 °C, significantly lower than the theoretical value for the bulk.

Synthesis, structural and magnetic characterizations of Li4Cu1-xNixTeO6 ( [formula omitted] = 0, 0.1, 0.2, 0.5, and 1)

We investigated the effect of Ni doping in a recently proposed quantum spin liquid (QSL) candidate Li4CuTeO6. We performed a comprehensive study on the structural and magnetic properties. We find that the anti-site disorder between Li+ and Cu2+ persists until 50% Ni doping in which Ni and Cu occupy different crystallographic sites. As a result, while Cu sits in both triangular and honeycomb layers in Li4CuTeO6, Ni forms only honeycomb layer in Li4NiTeO6 and Li4Cu0.5Ni0.5TeO6. Our magnetic susceptibility measurements show that the Weiss temperature decreases from -145.68 K in Li4CuTeO6 to -6.15 K in Li4NiTeO6 as Ni doping increases, and find no hint of magnetic ordering or freezing down to 1.8 K. Our analysis implies the existence of abundant low energy excitations in these materials.

Polarized Raman scattering and magnetic ordering in Mn lightly doped van der Waals Cr1−xMnxGeTe3 crystals

A layered van der Waals ferromagnet CrGeTe3 has attracted considerable interest due to the great potential for exploring low-power functional spintronic devices. However, research on the incorporation of chemical substitution in CrGeTe3 to tune the lattice vibrations and magnetic interactions is still lacking. In this work, an understanding of the phonon property and magnetic orders in Mn lightly doped Cr1−xMnxGeTe3 single crystals has been reported. It is found that the phonon symmetries are preserved over the studied Mn substitution content, as confirmed by angle-resolved polarized Raman spectroscopy and first-principles calculations. Furthermore, clear signatures of improved ferromagnetic Curie–Weiss temperature and magnetic moment are observed by detailed magnetic measurements. The higher magnetic moment of Mn ions, the variation of Mn–Te–Cr angle, Mn-induced hole doping, and the concomitant strain effect may all contribute to the enhanced ferromagnetism. Overall, our results demonstrate that chemical substitution is an effective pathway to engineering the lattice and magnetism of CrGeTe3.

Photo-induced reversible modification of the Curie–Weiss temperature in paramagnetic gadolinium compounds

Gadolinium oxyhydride GdHO is a photochromic material that darkens under illumination and bleaches back by thermal relaxation. As an inorganic photochromic material that can be easily deposited by magnetron sputtering, GdHO has very interesting potential applications as a functional material, specially for smart glazing applications. However, the underlying reasons behind the photochromic mechanism – which can be instrumental for the correct optimisation of GdHO for different applications – are not completely understood. In this paper, we rely on the well-established magnetic properties of Gd3+ to shed light on this matter. GdHO thin films present paramagnetic behaviour similar to other Gd3+ compounds such as Gd2O3. Illumination of the films result in a reversible increase of the Curie–Weiss temperature pointing to Ruderman–Kittel–Kasuya–Yosida RKKY interactions, which is consistent with the resistivity decrease observed in the photodarkened films.

Wolframite-type MnMoO4: Magnetization, sintering by Cool-SPS, and magnetodielectric effect

Dense ceramic samples of wolframite-type MnMoO4 (w-MnMoO4) have been prepared by Cool-SPS (Spark Plasma Sintering) for the first time with the goal of investigating the magnetic, dielectric, and magneto-electric properties of this thermally fragile polymorph of MnMoO4. Earlier studies found that w-MnMoO4 converts to the structurally different α-MnMoO4 phase if heated in air at 873 K, thus hindering fabrication of w-MnMoO4 ceramics by conventional high-temperature sintering. Unsintered powder samples, which were prepared via a hydrothermal method, and dense ceramics elaborated by Cool-SPS have the same magnetic properties. Magnetic susceptibilities display Curie-Weiss behaviour, χ = C/(T-θ), with effective moments for Mn2+ ion μeff ≈ 5.9 μB/Mn-atom and negative Weiss temperatures θ ≈ - 96 to - 98 K. Unlike the isostructural multiferroic compounds MnW1-xMoxO4 (0 ≤ x < 0.3) which exhibits at least two successive magnetic transitions below 15 K, w-MnMoO4 undergoes only one paramagnetic-to-antiferromagnetic transition at TN ≈ 32 K. The field-dependent magnetization at 2 K shows a spin-flop transition at μ0HSF ≈ 2 T. Capacitance and dielectric losses obtained for a ceramic between 2 and 300 K in zero field and in a field of 9 T reveal several weak anomalies. Dielectric anomalies are observed at the magnetic phase transition, suggesting a magnetoelectric coupling. Qualitatively different dielectric and magnetodielectric behaviours occur in α-MnMoO4 ceramics at low temperature.