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Spin-orbit coupled honeycomb magnets with the Kitaev interaction have received a lot of attention due to their potential of hosting exotic quantum states including quantum spin liquids. Thus far, the most studied Kitaev systems are 4d/5d-based honeycomb magnets. Recent theoretical studies predicted that 3d-based honeycomb magnets, including Na2Co2TeO6 (NCTO), could also be a potential Kitaev system. Here, we have used a combination of heat capacity, magnetization, electron spin resonance measurements alongside inelastic neutron scattering (INS) to study NCTO's quantum magnetism, and we have found a field-induced spin disordered state in an applied magnetic field range of 7.5 T < B (vertical to b-axis) < 10.5 T. The INS spectra were also simulated to tentatively extract the exchange interactions. As a 3d-magnet with a field-induced disordered state on an effective spin-1/2 honeycomb lattice, NCTO expands the Kitaev model to 3d compounds, promoting further interests on the spin-orbital effect in quantum magnets., 19 pages and 5 figures for main text. 16 pages and 6 figures for Supplemental Material

High-quality epitaxial LaCoO3 (LCO) thin films have been deposited on SrTiO3 (STO) substrates with pulsed laser deposition (PLD). We find that the LCO films undergo a typical ferromagnetic–paramagnetic (FM–PM) phase transition at ∼80 K. To understand the nature of magnetic phase transition, various methods, including the modified Arrott plot and critical isotherm analysis, were used to determine the critical exponents, which are β = 0.754(1) with a Curie temperature TC = 79.8(8) K and γ = 1.52(2) with TC = 79.9(2) K. The reliability of these critical exponents was confirmed using the Widom scaling relation and the scaling hypothesis. Further analysis revealed that the spin coupling within the LCO films exhibits two-dimensional (2D) long-range magnetic interaction and the magnetic exchange distance decays as J(r) ∼ r−(3.46). Our critical behavior analysis may shed new light on the further understanding of the origin of FM and the relatively fixed TC in LCO thin films.

We report a local probe investigation of the frustrated antiferromagnet ${\mathrm{Pr}}_{3}{\mathrm{BWO}}_{9}$ with a distorted kagome lattice. The absence of magnetic order or spin-freezing is indicated by a spectral analysis down to 0.3 K and by specific heat measurements down to 0.09 K. The Knight shifts show an upturn behavior with the sample cooling down, which is further suppressed by the external field. For the spin dynamics, gapped spin excitation is observed from the temperature dependence of spin-lattice relaxation rates, with the gap size proportional to the applied magnetic field intensity. Comparatively, an unexpected sharp peak is observed in the nuclear spin-spin relaxation rate data at ${T}^{*}\ensuremath{\sim}4\text{--}5$ K. These results indicate an unconventional persistent fluctuating paramagnetic ground state with antiferromagnetic collective spin excitations in the strongly frustrated spin system.

Barocaloric (BC) materials are a type of promising solid-state refrigerant that can be used in future refrigerators. Besides the routine pressure-driven lattice entropy change, spin or polar degrees of freedom often make considerable contributions. Relatively, little attention has been paid to the electronic contribution. Here we demonstrate a sizable electronic entropy change under pressure in hexagonal Ni1−xFexS due to the remarkable modification of its electronic structure. Accordingly, the total entropy change reaches 52.8 J kg−1 K−1 under only 100 MPa, which places Ni1−xFexS among the giant BC materials. Again, because of the electronic contribution, the thermal conductivity of Ni1−xFexS is higher than the reported values of other giant BC materials, which can boost the cooling efficiency. Our work would inspire the study of the giant BC effect with good thermal conductance in a wide range of electronic phase transition materials.

Magnetic skyrmions, being one of the most promising candidates for the next generation memory-type application due to their nanometer-size and efficient current-driven dynamics, are mainly found and studied in alloy helimagnets in which the spin-orbit coupling induced by Dzyaloshinskii-Moriya interaction (DMI) enables noncollinear spin alignment and skyrmion formation. In this paper, we report a possible finding of skyrmions crystal near room-temperature in centrosymmetric structures perovskite manganite La 0.8 Sr 0.2 MnO 3 (LSMO). Based on the measurements of isothermal magnetization around the Curie temperature (∼298 K), an unusual magnetic behavior of a discontinuous magnetization was observed and existed only at moderate magnetic field region together with a narrow temperature range from 306 to 290 K. Apart from this range, all curves return to conventional magnetic behavior of continuous change with external magnetic field. This characteristic has been frequently observed in some reported helimagnets (such as FeGe, MnSi), implying the possible existence of skyrmions crystal in LSMO. To further unveil the physical origin and underlying mechanisms, we performed the first-principles calculation for LSMO compound and a large DMI ( Δ E DMI = 13.46 meV, d 1 = 1.68 meV) was found to exists at the interface of LaMnO 3 / SrMnO 3 layers. This result not only supports our experimental findings in the present composition but also is consistent with the formation mechanism of magnetic skyrmions.

Electronic phase separation (EPS) plays a key role in elucidating the effects of complexity on emergent behavior for correlated electronic materials. In this work, we thoroughly studied a robust EPS existed in perovskite manganite La0.825Sr0.175MnO3. Results show that a typical paramagnetic-ferromagnetic (PM-FM) phase transition and a metallic-insulating phase transition occur at 285.4 and 295 K, respectively. Electron paramagnetic resonance (EPR) spectroscopy confirms that there are a double peaks rather than a single peak structures in the temperature region of 290 K ≤ T ≤ 315 K, indicating that an obvious EPS state generates in this compound. Based on the variation of EPR intensities, we found that the FM composition continues to increase with the decrease of temperature in the whole EPS region. Moreover, it causes a percolative-like metallic-insulting transition when the percolative threshold approach ∼22.63 % which is nearly equivalent to 25.34 % obtained by calculating the ratio of spontaneous magnetization against theoretical saturated magnetization. Detailed phase diagram shows that the EPS state not only occupies most of PM region but also a state of multiphase coexistence is also found.

High-quality epitaxial LaCoO

Barocaloric (BC) refrigeration is a new type of clean and energy-efficiency refrigeration technology. However, the giant and colossal BC effects are mainly based on the first-order phase transitions, leading to the unfavorable hysteresis. Here we report the giant BC effect along with weak hysteresis at the antiferromagnetic (AFM) to paramagnetic (PM) phase transition (TN =283 K) in antiperovskite PdNMn 3 compound. The reversible isothermal entropy change reaches 28.3 J kg-1K-1 under 290 MPa. The hysteresis is only about 2 K, which is associated with a small volumetric change ΔV/V at TN (~0.2%). The magnetic entropy is proposed to mainly contribute to the entropy change at TN , which compensates for the reduced lattice contribution due to the small ΔV/V . Our result demonstrates the possibility of realizing giant BC effect together with weak hysteresis in materials where both crystallographic and non-crystallographic entropy changes cooperate at the first-order phase transition (FOPT).

In this paper, we study the spin excitation properties of the frustrated triangular-lattice antiferromagnet $\mathrm{Yb}{({\mathrm{BaBO}}_{3})}_{3}$ with nuclear magnetic resonance. From the spectral analysis, neither magnetic ordering nor spin freezing is observed with temperature down to $T=0.26$ K, far below its Curie-Weiss temperature $|{\ensuremath{\theta}}_{w}|\ensuremath{\sim}2.3$ K. From the nuclear relaxation measurement, precise temperature-independent spin-lattice relaxation rates are observed at low temperatures under a weak magnetic field, indicating the gapless spin excitations. Further increasing the field intensity, we observe a spin excitation gap with the gap size proportional to the field intensity. These phenomena suggest a very unusual strongly correlated quantum disordered phase, and the implications for the quantum spin liquid state are further discussed.

Magnetoelectric materials are attractive for several applications, including actuators, switches, and magnetic field sensors. Typical mechanisms for achieving a strong magnetoelectric coupling are rooted in transition metal magnetism. In sharp contrast, here we identify CsEr(MoO4)2 as a magnetoelectric material without magnetic transition metal ions, thus ensuring that the Er ions play a key role in achieving this interesting property. Our detailed study includes measurements of the structural, magnetic, and electric properties of this material. Bulk characterization and neutron powder diffraction show no evidence for structural phase transitions down to 0.3 K and therefore CsEr(MoO4)2 maintains the room temperature P2/c space group over a wide temperature range without external magnetic field. These same measurements also identify collinear antiferromagnetic ordering of the Er3+ moments below TN = 0.87 K. Complementary dielectric constant and pyroelectric current measurements reveal that a ferroelectric phase (P ~ 0.5 nC/cm2) emerges when applying a modest external magnetic field, which indicates that this material has a strong magnetoelectric coupling. We argue that the magnetoelectric coupling in this system arises from a pseudo Jahn-Teller distortion induced by the magnetic field., Comment: 9 pages, 8 figures, under revision for resubmission

$\mathrm{NaYb}{\mathrm{O}}_{2}$ has been reported as a possible host for the quantum spin-liquid state. Here, the composition-dependent polycrystalline $\mathrm{N}{\mathrm{a}}_{1\text{\ensuremath{-}}x}\mathrm{Yb}{\mathrm{O}}_{2}$ ($x=0$, 0.03, and 0.07) has been investigated by combining high-field magnetizations and inelastic neutron scattering techniques. For the $x=0$ sample, no signature of a magnetic order is observed down to 0.3 K. Inelastic neutron scattering measurement suggests a continuous low-energy excitation spectrum centered at momentum transfer $(Q)\ensuremath{\sim}1.25\phantom{\rule{0.16em}{0ex}}{\AA{}}^{\ensuremath{-}1}$ and extending up to energy transfer ($E$) \ensuremath{\sim} 2.0 meV. In contrast, $x=0.03$ and 0.07 samples exhibit magnetic transitions at 1.1 and 2.3 K, respectively. High-field magnetization measurements indicate similar behaviors for $x=0$ and 0.03 samples including plateaulike features at the 1/3 saturated magnetization, which implies that the spin disorder in the $x=0$ sample might be suppressed preceding the emergence of the up-up-down phase. This composition- and field-dependent study allows us to construct complete phase diagrams indicating that $\mathrm{NaYb}{\mathrm{O}}_{2}$ is a promising candidate for the quantum spin-liquid state in close proximity to the antiferromagnetic instability tuned by the application of magnetic fields as well as controlling the concentration of $\mathrm{N}{\mathrm{a}}^{+}$ ion vacancies.

The structural, Hall effect, electronic transport, and magnetic properties of Ge0.96−xBixFe0.04Te epitaxial thin film as prepared by pulsed laser deposition technique were reported. X-ray diffraction patterns including linear scans and phi scans confirmed that all films are high quality epitaxy and crystallinity. With the substitution of high valence Bi for Ge element, we found that the previous carriers of hole were changed to electron, which was testified by the negative slopes obtained from the measurements of Hall effect under different temperatures. The electronic transports show a typical semiconductor behavior and can be understood by the small polaron hopping model because the lattice distortions increase the electron-phonon interaction. An obvious ferromagnetic properties occur in the high Bi-doping Ge0.64Bi0.32Fe0.04Te rather than in that with low Bi-doping concentration, indicating that the ferromagnetic establishment is entirely dependent on carrier’s transmissions. The first-principles calculation performed on this system also reveals that the ferromagnetic state exactly exists in the present n-type diluted magnetic semiconductors with Bi co-dopants.

The Cr ion doped Y-type hexaferrite Ba0.5Sr1.5Zn2Fe11.4Cr0.6O22 has been found to be a promising magnetoelectric material for the non-zero spontaneous electric polarization that can be reversed by a relatively low magnetic field. However, it remains an open question what the underlying mechanism of the magnetoelectric correlation is and how this correlation evolves with the varying temperature and magnetic field. Here we establish a detailed phase diagram via the combined measurements and analyses of magnetization, dielectric constant, and electric polarization. Various magnetic and ferroelectric phases are discovered for different scales of temperature and magnetic field, as well as the complicated and intriguing phase transitions. A newly emerging transition at 183 K separates the low-field ferroelectric phase into two regions with reversal and non-reversal polarizations, respectively, which is rarely observed among various magnetoelectric ferrites. Possible field-dependent magnetic structures are proposed to qualitatively explain this transition.

Interstitial iron ( Fe i ) has strong influence on physical properties of Fe 1 + x Sb (0.08 ⩽ x ⩽ 0.38) compounds. We synthesized Fe 1.08 Sb single crystals with Fe i content close to the lower limit of solution area and investigated its transport and magnetic properties. The ac susceptibility and field dependence of magnetization measurements demonstrate that the transition at ∼9 K is a spin glass transition. By analyzing temperature dependence of susceptibility ( χ vs T) and resistivity (d2 ρ /dT2 vs T) results, we found a change of scattering in transport properties caused by the ordering of Fe i moments in this compound. In addition, the Hall resistivity results reveal that the hole-type carrier is dominant and the topological Hall effect induced by spin chirality is negligible in Fe 1.08 Sb.

The present paper investigates the magnetic and magnetoelectric properties of Bi2Ir2−xMnxO7 compounds with respect to the degree of Mn doping denoted by x. It is found that the antiferromagnetic (AFM) interactions are initially enhanced with increasing x, but are then weakened with further increases in x. These findings are explained on the basis of the competition among AFM Ir–Ir, AFM Ir–Mn, and ferromagnetic Mn–Mn interactions. In addition, the electric transport properties at the temperature range studied present a metal-insulator transition in the range 0.05 ≤ x ≤ 0.15, while an insulating state occurs for x > 0.15 because of electron localization. At low temperatures, a small positive magnetoresistance (MR) effect is observed for x = 0, whereas a negative MR effect is observed for all Mn-doped samples. The 3d–5d electron interactions play a dominant role in determining the magnetic properties of the doped samples.

The critical behaviors of the perovskite La0.5Sr0.5MnO3 nanowires bundles around the ferromagnetic-paraferromagnetic (FM-PM) transition through modified Arrott plot and critical isothermal analysis is investigated. The obtained critical exponents are determined by modified Arrott Noakes equation ( H / M ) 1 / γ = ( T − T c ) / T c + ( M / M 1 ) 1 / β under a low external magnetic field of 0–0.8T, where β = 0.93 and γ = 2.25 were obtained at Tc ≈ 328 k. The availability of the parameters is proved by fulfilling the Widom scaling relation δ = 1 + γ / β which obeys the single scaling equation of M ( H , | e | ) = e β f ± ( H / | e | β + γ ) . The critical exponents determined in this system is unique and not following theories in any published literature. It may be attributed to the nano-size effect and surface magnetism of this system.

Significance Searching for topological superconductors is of paramount importance in condensed-matter physics and materials science today: these materials are expected to harbor Majorana fermions on the edge states, an essential component for topological quantum computation platform. We experimentally observed s +− pairing two-gap superconductivity and type-II Weyl semimetal property in T d -phase MoTe 2− x S x ( x ≈ 0.2). Further, an enhanced surface superconducting gap comparing to bulk gaps is discovered. Our findings are strongly suggestive of topological superconductivity of the T d -phase MoTe 2− x S x . This work not only presents an important breakthrough in searching for topological superconductors but also inspires further investigations on the sign-change superconductivity beyond Fe-based high-T c superconductors.

Electron paramagnetic resonance (EPR) was applied extensively to probe the phase separation and spin relaxation mechanism in the perovskite manganites. In this study, we conducted the measurement of EPR for the perovskite manganites (La0.5Pr0.5)0.67Ca0.33MnO3. We found that both paramagnetic and ferromagnetic resonance peaks simultaneously emerged on resonance spectrum near below TC, exhibiting a typical characteristic of phase separation. The linewidth of EPR spectrum progressively enlarged upon the rising of temperature in the temperature range of T > T C and a quasilinear variation of peak-peak width was observed at TC T 500 K. In contrast to the usual beliefs that the variation of peak-peak linewidth can be understood either by spin-lattice relaxation or by spin-spin relaxation, however, the linewidth behavior observed here shows a coexistence of two spin relaxation mechanisms. We proposed that the inhomogeneous electronic phases due to the intrinsic self-organizing growth were responsible for the appearance of multiple spin exchange interactions and variational relaxation mechanism. This finding would be possible to pave a new way for further investigating magnetic correlations and spin dynamics in the paramagnetic hole-doped manganites.

In this study, we investigated the structural, magnetic phase transition, and magnetocaloric properties of bilayer perovskite manganite La 1.38 Sr 1.62 Mn 2 O 7 based on X-ray diffraction, electron paramagnetic resonance, and temperature-/magnetic field-dependent magnetization measurements. The structural characterization results showed the prepared sample had a tetragonal structure with the space group I 4/ mmm . The Curie temperature was determined as 114 K in the magnetization studies and a second-order paramagnetic-ferromagnetic transition was confirmed by the Arrott plot, which showed that the slopes were positive for all the curves. According to the variation in the electron paramagnetic resonance spectrum, we detected obvious electronic phase separation across a broad temperature range from 220 to 80 K in this magnetic material, thereby indicating that the paramagnetic and ferromagnetic phases coexist above as well as below the Curie temperature. Based on a plot of the isothermal magnetization versus the magnetic applied field, we deduced the maximum magnetic entropy change, which only reached 1.89 J/kg.K under an applied magnetic field of 7.0 T. These theoretical investigations indicated that in addition to the magnetoelastic couplings and electron interaction, electronic phase separation and anisotropic exchange interactions also affect the magnetic entropy changes in this bilayer manganite.

Microscopic magnetic interactions and magnetism can be probed by studying the critical paramagnetic–ferromagnetic phase transition of magnetic materials. In this work, the critical behavior of the lightly Ga-doped manganites Nd0.55Sr0.45Mn0.98Ga0.02O3 (NSMGO) has been investigated. Scaling analysis reveals the critical exponents β = 0.308, γ = 1.197, and δ = 4.916, where their self-consistency and reliability are verified by the Widom scaling law and the scaling equation. These exponents indicate that the magnetic phase transition in NSMGO belongs to the anisotropic 3D-Ising universality class. Nevertheless, the asymptotic critical exponents βeff and γeff are found to approach to the values of 3D-Heisenberg model, implying the existence of isotropic short-range magnetic interactions. We suggest that, although the Nd-based manganites possess a strong magnetocrystalline anisotropy, this effect can be partly averaged out in view of the present polycrystalline NSMGO. Therefore, in the asymptotic critical region, the phase transition reveals the crossover from the scaling of 3D-Ising toward 3D-Heisenberg universality class.

We investigated the magnetic properties of a geometrically frustrated magnet of ZnFe2O4 nanoparticles by carrying out the comprehensive measurements of dc magnetization and ac susceptibility. Spin glass is confirmed to occur in this weakly Fe(Zn)-ionic-inversed sample. The common characteristics of spin glass including the aging, the memory, and the rejuvenation effects were observed. By using the critical-power law to study the spin dynamics, the spin-glass transition temperature Tg is obtained to be 18 K and the dynamic exponent zν is 8.0. The weak exchange interaction disorder introduced by the ferrimagnetic JAB interaction, together with the weak nonmagnetic dilute disorder induced by the ionic inversion, is responsible for the formation of spin glass in the ZnFe2O4 nanoparticles.

Understanding the mechanisms for forming skyrmionic spin configurations at room temperature is essential for exploring the applicable spintronics devices based on topological spin textures. In this work, the anisotropic magnetic properties and critical behavior are investigated in noncollinear itinerant magnet PrMn2Ge2. The strongly anisotropic magnetic interactions and magnetic field and temperature induced antiferromagnetic to ferromagnetic transition are observed. The critical behavior of high temperature ferromagnetic transition at 331 K was analyzed, and the critical exponents β = 0.335, γ = 0.878, and δ = 3.617 are extracted by the modified Arrott plot method, which lie between the values of long-range mean-field and short-range three-dimensional theories, demonstrating that PrMn2Ge2 possesses multiple magnetic interactions. This is also confirmed by the moderated interaction function, which is decay as J( r) ∼ [Formula: see text]. Therefore, the competition of multiple magnetic interactions in PrMn2Ge2 is analogous to what has been observed in GdRu2Si2 and could be the origin of skyrmionic bubbles observed at room temperature.

Large-scale growth of two-dimensional (2D) ferromagnetic thin films will provide an ideal platform for studying 2D magnetism and active spintronic devices. However, controllable growth of 2D ferromagnets over large areas faces tremendous challenges. Herein, we report a large-area growth of 2D ferromagnetic single-crystal thin films Cr4Te5 on Al2O3 (0001) substrates using pulsed laser deposition. X-ray diffraction patterns and atomic force microscopy detection confirm that all thin films have high quality epitaxy together with being atom-level smooth. Magnetic measurements show the persistence of ferromagnetic ordering state to above room temperature, with a Curie temperature ∼320 K, atomic magnetic moment ∼0.307 μ B /Cr, and the easy-magnetization axis in the film plane. Comparing with bulk Cr4Te5 single-crystal, the critical exponent β = 0.491 indicates that the magnetic interactions of the thin film obey the mean-field model rather than the 3D Heisenberg model. This work will open an avenue for growing large-scale 2D ferromagnets and developing room temperature 2D magnet-based nanodevices.

Barocaloric (BC) refrigeration is a new type of clean and energy-efficiency refrigeration technology. However, the giant and colossal BC effects are mainly based on the first-order phase transitions, leading to the unfavorable hysteresis. Here we report the giant BC effect along with weak hysteresis at the antiferromagnetic (AFM) to paramagnetic (PM) phase transition (TN = 283 K) in antiperovskite PdNMn3 compound. The reversible isothermal entropy change reaches 28.3 J kg−1 K−1 under 290 MPa. The hysteresis is only about 2 K, which is associated with a small volumetric change ΔV/V at TN (~0.2%). The magnetic entropy is proposed to mainly contribute to the entropy change at TN, which compensates for the reduced lattice contribution due to the small ΔV/V. Our result demonstrates the possibility of realizing giant BC effect together with weak hysteresis in materials where both crystallographic and non-crystallographic entropy changes cooperate at the first-order phase transition (FOPT).

In this work, the resistivity and magnetization of Bi 2 Ir 2 O 7 are investigated under hydrostatic pressure. At ambient pressure, the resistivity of Bi 2 Ir 2 O 7 exhibits a metallic behavior with the decrease of temperature. When the pressure is applied, a metal-insulator phase transition at low temperature is induced under a pressure of ∼ 0.48 GPa. The metal-insulator phase transition temperature ( T MI ) increases linearly with pressure as d T MI / dP = 3.4 ± 0.3 K / GPa . The temperature dependence of resistivity [ ρ ( T ) ] in the pressure-induced insulating phase exhibits a thermal activation behavior ( ρ = ρ 0 e Δ E / k B T ) , where the thermal activation energy ( Δ E ) increases monotonously with the pressure. Meanwhile, the magnetization is enhanced by the pressure, which indicates an enhancement of magnetic ordering. The results suggest that localization occurs due to the magnetic ordering induced by the pressure, which confirms the magneto-electronic coupling in Bi 2 Ir 2 O 7

The magnetic entropy change [Δ S M ( T , H )] around the phase transition temperature T C is investigated by the scaling method for Fe 0.5 Co 0.5 Si, which exhibits a Skyrmion phase below T C . The parameters of Δ S M ( T , H ) exhibit field dependent behaviors. The Δ S M ( T , H ) curves under high field can be well scaled into a single universal curve independent of external field and temperature. However, Δ S M ( T , H ) curves under low field become divergent just below T C , which indicates a characteristic of first-order transition. The scaling investigation of Δ S M ( T , H ) curves indicates that the phase transition in Fe 0.5 Co 0.5 Si is of a weak first-order type in low field region, while it is driven into a second-order one under high field. This weak first-order phase transition in low field region resembles that in typical skyrmion system MnSi which is caused by the critical fluctuation. The result suggests that critical fluctuation plays an important role in the phase transition and formation of skyrmion state.

We report a detailed study of magnetic properties in manganite (La0.5Pr0.5)0.67Ca0.33MnO3. In contrast to the usual beliefs, it shows an abnormal upturn deviation from the Curie–Weiss law on the inverse susceptibility curve. Such a non-Griffiths-like phase is further confirmed from the inverse double integrated intensities of electron paramagnetic resonance spectrum. Because La $$^{3+}$$ ions are substituted by Pr $$^{3+}$$ ions with 50% concentrations, the ratio of three ions (La $$^{3+}$$ , Pr $$^{3+}$$ , Ca $$^{2+}$$ ) is close to 1 on A-site sublattice. As a result, some short-range antiferromagnetic (CO AFM) phases come into being in the system due to the existence of localized charge ordering states. Therefore, the upturn deviation from Curie–Weiss law originates from the appearance of short-range CO AFM correlations above $$T_{\text{C}}$$ . Additionally, a magnetic field-driven-metamagnetic transition is found, which gives a main contribution for the large magnetic entropy change (MEC) observed in this sample. Both the Arrott plot and the renormalized MEC curves testify that this transition belongs to first-order magnetic transition. The insignificant hysteresis loop indicate that the inevitable thermal hysteresis can be ignored in the present first-order material implying that it is a potential candidate for the cryogenic temperature magnetic refrigeration.

Co3Sn2S2, a quasi-two-dimensional system with kagome lattice, has been found as a magnetic Weyl semimetal recently. In this work, the anisotropies of magnetization and transport properties of Co3Sn2S2 were investigated. The high field measurements reveal a giant magnetocrystalline anisotropy with an out-of-plane saturation field of 0.9 kOe and an in-plane saturation field of 230 kOe at 2 K, showing a magnetocrystalline anisotropy coefficient Ku up to 8.3 * 10^5 J m-3, which indicates that it is extremely difficult to align the small moment of 0.29 {\mu}B/Co on the kagome lattice from c axis to ab plane. The out-of-plane angular dependences of Hall conductivity further reveal strong anisotropies in Berry curvature and ferromagnetism, and the vector directions of both are always parallel with each other. For in-plane situation, the longitudinal and transverse measurements for both I parallel a and I perpendicular a cases show that the transport on the kagome lattice is isotropic. These results provide essential understanding on the magnetization and transport behaviors for the magnetic Weyl semimetal Co3Sn2S2.

We report magnetization, heat capacity, thermal expansion, and magnetostriction measurements down to millikelvin temperatures on the triangular antiferromagnet YbMgGaO4. Our data exclude the formation of the distinct 13 plateau phase observed in other triangular antiferromagnets, but reveal plateaulike features in second derivatives of the free energy, magnetic susceptibility, and specific heat, at μ0H=1.0-2.5 T for H∥c and 2-5 T for H⊥c. Using Monte Carlo simulations of a realistic spin Hamiltonian, we ascribe these features to nonmonotonic changes in the magnetization and the 12 plateau that is smeared out by the random distribution of exchange couplings in YbMgGaO4. © 2020 American Physical Society. We would like to thank Yaroslav Kvashnin for technical assistance with the UppASD package. The work in Augsburg was supported by German Research Foundation Project No. 107745057 (TRR80) and by the Federal Ministry for Education and Research through the Sofja Kovalevkaya Award of the Alexander von Humboldt Foundation (A.A.T.). The work of I.A.I. and V.V.M. was supported by Russian Science Foundation Grant No. 18-12-00185. Q.M.Z. was supported by the National Key Research and Development Program of China (2017YFA0302904 and 2016YFA0300500) and the NSF of China (11774419 and U1932215).

The physical properties of itinerant ferromagnet [Formula: see text]-Co

Experimental and theoretical studies are performed on ${\mathrm{La}}_{3}{\mathrm{Ir}}_{3}{\mathrm{O}}_{11}$, an iridate hosting a $+4.33$ fractional valence state for Ir ions and a three-dimensional frustrated structure composed of edge-shared ${\mathrm{Ir}}_{2}{\mathrm{O}}_{10}$ dimers. These features are expected to enhance intersite hoppings and reduce magnetic moments of Ir ions. However, a spin-orbit driven Mott insulating transport is observed, which is supported by our first-principles calculations. Most importantly, geometrical frustration and competing interactions result in a non-Curie-Weiss paramagnetic ground state, revealing no magnetic order down to 2 K. This unusual state is further demonstrated by a theoretical modeling process, suggesting a possible candidate for the spin-liquid state.

Nontrivial spin configurations tend to bring about novel transport properties in magnetic materials. We report the magnetic anisotropy and topological Hall effect in trigonal ${\mathrm{Cr}}_{5}{\mathrm{Te}}_{8}$ single crystals. Below the magnetic transition temperature, the spins are canted ferromagnetic aligned along $c$ axis with antiferromagnetic components in $ab$ plane. This peculiar magnetic structure gives rise to the anisotropic anomalous Hall effect (AHE) in ${\mathrm{Cr}}_{5}{\mathrm{Te}}_{8}$. When the current flows along the $ab$ plane, ${\mathrm{Cr}}_{5}{\mathrm{Te}}_{8}$ exhibits a conventional AHE depicted by skew scattering mechanism. On the other hand, the topological Hall effect appears with current along $c$ axis, which stems from the noncoplanar spin configuration with scalar spin chirality during the spin flop process.

Magnetism of the $S$ = 1 Heisenberg antiferromagnets on the spatially anisotropic square lattice has been scarcely explored. Here we report a study of the magnetism, specific heat, and thermal conductivity on Ni[SC(NH$_2$)$_2$]$_6$Br$_2$ (DHN) single crystals. Ni$^{2+}$ ions feature an $S$ = 1 rectangular lattice in the $bc$ plane, which can be viewed as an unfrustrated spatially anisotropic square lattice. A long-range antiferromagnetic order is developed at $T \rm_N =$ 2.23 K. Below $T\rm_N$, an upturn is observed in the $b$-axis magnetic susceptibility and the resultant minimum might be an indication for the $XY$ anisotropy in the ordered state. A gapped spin-wave dispersion is confirmed from the temperature dependence of the magnetic specific heat. Anisotropic temperature-field phase diagrams are mapped out and possible magnetic structures are proposed.

We have presented the structural, surface morphology, magnetic and resistivity data for perovskite LaMnO3 epitaxial thin films which are fabricated on well-oriented (001) LaAlO3 substrates by pulsed laser deposition technique. X-ray diffraction [Formula: see text]–[Formula: see text] linear scans and reciprocal space mapping measurement confirm that the out-of-plane and in-plane epitaxial relationship are LMO(001)/LAO(001) and LMO(110)/LAO(110), respectively. Surface roughness determined by atomic force microscopy was no more than 0.3 nm. In the whole studied temperature range, all films only show a paramagnetic behavior instead of any magnetic phase transitions. Correspondingly, the electron transport behaviors always exhibit an insulting state as the temperature changes from high to low. However, we find that none of theoretical models can individually be used to understand their conductive mechanisms. Further studies indicated that charge carries of high and low temperature region obey adiabatic and nonadiabatic small polaronic hopping mechanisms, respectively. This finding offers new ways of exploiting the abnormal ferromagnetism in LaMnO3 multilayer thin films.

We report our nuclear magnetic resonance (NMR) study on the structurally spin chain compound Ni2NbBO6 with complex magnetic coupling. The antiferromagnetic transition is monitored by the line splitting resulting from the staggered internal hyperfine field. The magnetic coupling configuration proposed by the first-principle density functional theory (DFT) is supported by NMR spectral analysis. For the spin dynamics, a prominent peak at T ∼ 35 K well above the N éel temperature (T N ∼ 20 K at μ 0 H = 10 T) is observed from the spin-lattice relaxation data. As compared with the dc-susceptibility, this behavior indicates an antiferromagnetic coupling with the typical energy scale of ∼3 meV. Thus, the Ni2NbBO6 compound can be viewed as strongly ferromagnetically coupled armchair spin chains along the crystalline b-axis. These facts place strong constraints on the theoretical model for this compound.

Critical phenomenon of the noncentrosymmetric Cr11Ge19, which exhibits an itinerant ferromagnetic ground state, is investigated by scaling of the magnetic entropy change [ΔSM(T,H)]. It is found that parameters δFWHM (the full width at half maximum), − Δ S M m a x (the maximum of the magnetic entropy change), and RCP (the relative cooling power) of ΔSM(T) are governed by the power law of critical exponents. With the critical exponents, ΔSM(T,H) curves are scaled into a universal curve independent of temperature and field, which suggests that the magnetic transition is of a second order type. The universal collapse of ΔSM(T,H) indicates that the critical behavior of Cr11Ge19 can be well described by the scaling laws for the critical phenomenon. Moreover, the ΔSM follows the power law of Hn with n(T,H)=dln|ΔSM|/dln(H). The temperature dependence of n values reach minimum at ∼ 71.5 K. Based on the magnetic specific change ΔCp(T,H), the actual magnetic transition temperature is strictly determined as TC=71.3±0.2 K for the single crystal Cr11Ge19.

Both $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{PdB}{\mathrm{i}}_{2}$ and $\ensuremath{\beta}\text{\ensuremath{-}}\mathrm{PdB}{\mathrm{i}}_{2}$ are superconductors with topological nontrivial signs. Here we report that the $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{PdB}{\mathrm{i}}_{2}$ superconductor is converted by pressure into the \ensuremath{\beta}-phase superconducting polymorph, with the superconductivity being further enhanced upon decompression. Through high-pressure resistance and synchrotron x-ray-diffraction experiments, we show that the \ensuremath{\alpha} phase transforms into the \ensuremath{\beta} phase at ${P}_{c}\ensuremath{\sim}8$ GPa, above which the superconductivity is robust up to the maximum pressure investigated in this work. More interestingly, when the applied pressure is gradually released from 42.9 down to 1.7 GPa, the ${T}_{c}$ increases monotonously from 2.5 to 4.0 K. We argue that the observed unusual evolution of superconductivity can be explained by combination of pressure-manipulated crystal quality and the pressure dependence of ${T}_{c}$ of the $\ensuremath{\beta}\text{\ensuremath{-}}\mathrm{PdB}{\mathrm{i}}_{2}$ superconductor.

The origin of the unusual second magnetic transition at a temperature ${T}_{M}$ in the ruthenate $\mathrm{S}{\mathrm{r}}_{4}\mathrm{R}{\mathrm{u}}_{3}{\mathrm{O}}_{10}$ remains elusive. Here, we have investigated the thickness-dependent anisotropic magnetoresistance of $\mathrm{S}{\mathrm{r}}_{4}\mathrm{R}{\mathrm{u}}_{3}{\mathrm{O}}_{10}$ nanosheets, and clearly found that the sign of the magnetoresistance (MR) presents an unusual reversal behavior from a positive to negative with an external magnetic field $H\ensuremath{\perp}ab$ plane or vice versa with $H\ensuremath{\parallel}ab$ plane when the temperature decreases across the ${T}_{M}$. Analysis of the data demonstrates that this MR reversal is caused by the magnetization reversal from the $ab$ plane ferromagnetic order at $Tg{T}_{M}$ to the $c$ direction at $Tl{T}_{M}$ due to the competition between the shape anisotropy and the inherent magnetocrystalline anisotropy. Our result suggests that the second magnetic transition in $\mathrm{S}{\mathrm{r}}_{4}\mathrm{R}{\mathrm{u}}_{3}{\mathrm{O}}_{10}$ nanosheets originates from a spin reorientation.

We report detailed dc and ac magnetic susceptibilities, specific heat, and thermal conductivity measurements on the frustrated magnet ${\mathrm{ZnCr}}_{2}{\mathrm{Se}}_{4}$. At low temperatures, with an increasing magnetic field, this spinel material goes through a series of spin state transitions from the helix spin state to the spiral spin state and then to the fully polarized state. Our results indicate a direct quantum phase transition from the spiral spin state to the fully polarized state. As the system approaches the quantum criticality, we find strong quantum fluctuations of the spins with behaviors such as an unconventional ${T}^{2}$-dependent specific heat and temperature-independent mean free path for the thermal transport. We complete the full phase diagram of ${\mathrm{ZnCr}}_{2}{\mathrm{Se}}_{4}$ under the external magnetic field and propose the possibility of frustrated quantum criticality with extended densities of critical modes to account for the unusual low-energy excitations in the vicinity of the criticality. Our results reveal that ${\mathrm{ZnCr}}_{2}{\mathrm{Se}}_{4}$ is a rare example of a 3D magnet exhibiting a field-driven quantum criticality with unconventional properties.

We report the experimental realization of a Dirac semimetal state in NdSb, a material with antiferromagnetic ground state. The occurrence of a topological semimetal state has been well supported by our band structure calculations and the experimental observation of chiral-anomaly-induced negative magnetoresistance. A field-induced Fermi surface reconstruction is observed in response to the change of spin polarization. The observation of a topological semimetal state in a magnetic material provides an opportunity to investigate the magnetotopological phenomena.

Bi 2− x Ca x Ir 2 O 7− δ ( x =0, 0.1, 0.2, 0.3, and 0.4) pyrochlore iridates were prepared by the solid-state reaction method in air. In this paper we reported a systematic study of hole-doped Bi 2− x Ca x Ir 2 O 7− δ by performing crystal structure, electrical transport and magnetic measurements. A high-crystallized Bi 2– x Ca x Ir 2 O 7– δ with a cubic structure was obtained. Because Bi 3+ was substituted in a random way by Ca 2+ which has relatively smaller ionic radius, disorder and phononic oscillations were induced and the the length of Ir–O bands were reduced. The doped samples were found to exhibit metal–insulator transition. Magnetic measurements on the doping samples indicated a shift towards nonmagnetic Ir 5+ , and the anti-ferromagnetism was weakened.

Highly ordered La0.5Ca0.5MnO3 nanowires bundles are synthesized using mesoporous SBA-15 silica as the hard template. The magnetic properties and critical behaviors of the ferromagnetic–paramagnetic (FM–PM) phase transition of the La0.5Ca0.5MnO3 nanowires bundles are investigated through isothermal magnetization methods. The calculated results show that the FM–PM transition is second order and the magnetic interaction has some deviations from the mean-field model. Though the obtained critical parameters of β = 0.596 ± 0.009, γ = 1.131 ± 0.008 and δ = 2.99 ± 0.05 follow the Widom scaling relation δ = 1 + γ/β and the single scaling equation M(H,|e|) = eβf±(H/|e|β+γ), the critical exponents do not obey the magnetization entropy scaling theory, indicating that the nanometer-size effect play a significant role on the magnetic phase transition and magnetic entropy for La0.5Ca0.5MnO3 nanowires bundles.