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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.

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.

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).

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.

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.

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.

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

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 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.

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.

We have studied the magnetic properties of spin-frustrated compound Dy 2 Ti 2− x V x O 7 single crystals. Bulk magnetization data show that ferromagnetic interaction enhances with increasing content of V, resulting from the ferromagnetic interactions between Dy and V ions. It is also found from ac susceptibility that the modestly doped samples ( x ≤0.4) still keep ice state, demonstrating the robustness of spin ice. When the doped concentration increases up to 0.5, more disorder on B site and internal field associated with V 4+ ions would affect the macroscopic ground-state degeneracy and relieve the frustration, leading to the disappearance of spin ice and occurrence of a spin-glass-like transition. The magnetic properties of the system are related to magnetic frustration and local structural disorder.

We presented the structural, magnetic, and magnetocaloric data for perovskite TmFeO3. XRD revealed distorted orthorhombic structure (Pbnm) for TmFeO3. Spin-reorientation transition was confirmed through magnetic susceptibility. −ΔSM(max) is 13.72 Jkg-1 K−1 at the temperature of 85 K under ΔH = 6 T, with the RCP value of 676 J/kg. −ΔSM(max) and RCP values were increased with the applied field, possibly due to the d-f exchange interactions. The magnetic hysteresis cycles are established for different values of temperatures. These properties make it a potential candidate used for magnetic refrigerants. For magnetic refrigeration application, very large refrigeration capacity is also required along with large entropy change value.

We have studied the magnetic and dynamical properties of spin-frustrated magnet Dy2Ti2−x FexO7 single crystals. Bulk magnetization data of the heavily Fe doped samples give a negative Curie–Weiss temperature, probably suggesting the existence of short-range antiferromagnetic interaction in Fe-doped samples. Dynamical analyses show that the doped system still freezes into an ice-like state but it is more dynamical than that in pure spin ice Dy2Ti2O7. Furthermore, the dynamic freezing of the spins is suppressed to lower temperatures, which is caused by the Dy-Fe spin interactions and the altered crystalline electric field. It is also found that the coordination number of Fe decreases at high doping level (x=0.15), leading to the change of the spin state of Fe3+.

Critical behaviors of the half-doped perovskite cobaltites Pr0.5Sr0.5 CoO 3 - Δ ( Δ = 0 and ∼0.16) are investigated around the critical temperatures by bulk magnetization study, where the critical exponents (β, γ and δ) are obtained. These critical exponents fulfill the Widom scaling law δ = 1 + γ β - 1 , indicating self-consistency and reliability of the obtained results. With the critical exponents, M – T – H curves collapse onto two independent universal branches below and above the critical temperatures. The critical exponents of the oxygen-nonstoichiometric Pr0.5Sr0.5 CoO 3 - Δ accord with the mean-field model exactly. However, for the oxygen-stoichiometric Pr 0.5 Sr 0.5 CoO 3 , β deviates to the theoretical prediction of three-dimensional Heisenberg model while γ and δ are close to that of mean-field model. These results indicate long-range ferromagnetic coupling in Pr0.5Sr0.5CoO3−Δ ( Δ = 0 and ∼0.16), which cannot be explained by the nearest-neighbor interaction proposed for the double-exchange mechanism. Instead, the collective effect of p - d hybridization and RKKY interaction of Pr 3 + f-electrons with the conduction electrons is suggested to be responsible for the long-range interaction. In addition, the discrepancy of β in the oxygen-stoichiometric Pr0.5Sr0.5CoO3 may be due to a short-range interaction corresponding to the extra crystalline phases in the oxygen-stoichiometric sample.

We employed x-ray diffractometer, electron microscope and magnetometer to study the structure and magnetic properties of polycrystalline MnSi. Pure and homogeneous MnSi phase can be obtained in a certain composition range. Intriguingly, our magnetic measurements indicate that the polycrystalline MnSi shows typical magnetic phase transitions as single crystals. The magnetic transformations between helical, conical, skyrmion and field-polarized states can be well detected in the field-dependent susceptibility curves. The similar magnetic behaviors observed for polycrystalline and single crystals make magnetometry an effective and straightforward route to identify skyrmions, especially useful for the materials that are hard to prepare single crystals or epitaxial thin films.

The temperature dependence of magnetization of Ba3Cr2O8 was investigated under an applied hydrostatic pressure of 0 and 1 GPa and analyzed based on the Curie–Weiss model and the Bleaney–Bowers model. Experimental results show that while the intradimer coupling J0 is hardly affected the interdimer interaction J ' is significantly weakened upon the application of pressure. The underlying magnetic behavior is presumably related to the subtle change of the lattice induced by the applied pressure.

The magnetic order and dynamical properties of spin-frustrated magnet Dy 2− x Yb x Ti 2 O 7 single crystals have been studied by dc and ac susceptibility measurements. It is found that the substitution of the Dy 3+ by the Yb 3+ in Dy 2 Ti 2 O 7 relaxes ferromagnetic coupling. In low Yb 3+ doping samples, a spin freezing peak at T f (T f T s associated with Dy 3+ are observed. With increasing Yb 3+ doping, a new peak marked by T ⁎ associated with Yb 3+ appears. We suggest that T ⁎ originates from the thermally activated spin fluctuations of Yb 3+ . It is also found that the relaxation process for T s becomes both thermally activated and quantum tunneled in x ≥1.0 samples. The low-temperature dynamical behaviors of Dy 2− x Yb x Ti 2 O 7 are dominated by the Dy–Yb spin interactions and the altered crystalline electric field. Moreover, crystal field-phonon coupling may contribute to the spin dynamic properties.

We grew pure 1T/2H-TaS2 single crystals via the chemical vapor transport (CVT) method and introduced defects into the samples by quenching. We systematically investigated the influence of defects on charge–density–wave (CDW) and superconductivity (SC) in 1T and 2H-TaS2. The defects can induce SC to 1T-TaS2 system, and inhibit the commensurate CDW (CCDW) and Mott insulator phase, the superconducting transition temperature ( T c Onset ) is about 2.5 K and the zero resistivity temperature ( T c zero ) is about 0.7 K. For 2H-TaS2, the defects nearly have no effect on CDW, while T c Onset is increased to about 2.7 K. The magnetization hysteresis loops show typical type-II superconductor behaviors for both 1T and 2H-TaS2 systems.

In this work, we successfully synthesize the single crystal Cr11Ge19. The magnetism of the noncentrosymmetric Cr11Ge19 with itinerant ferromagnetic ground state is thoroughly investigated on the single crystal. Based on the variation measurements including the angular rotation, temperature, and magnetic field dependence of magnetization, we find that this material exhibits strong magnetic anisotropy along the c-axis. To clearly reveal the magnetic interactions, the critical behavior is studied using the modified Arrott plot, the Kouvel-Fisher method, and the critical isotherm technique. Combining these different methods, three main critical exponents (β, γ, and δ) are obtained. The critical exponent β is close to the theoretical prediction of a three-dimensional XY model with spin-dimensionality n = 2, indicating two-dimensional magnetic coupling. Meanwhile, the critical exponent γ suggests that the magnetic interaction is of long-range type with magnetic exchange distance decaying as J(r) ≈ r−4.61. We propose that the ferromagnetic ground state of Cr11Ge19 is formed by the polarized magnetic moments along the c-axis, while the long-range magnetic coupling is established within the ab plane.

The effects of As doping on the superconductivity and magnetism in the Tl0.4K0.4Fe2−y Se2 superconductor are studied. We find that the As doping does not significantly change the occupancy at the Fe-site, meaning a certain amount of Fe ions changes its valence from 2+ to 3+. The superconductivity is gradually suppressed with increasing As doping. The magnetic measurements suggest that though the As doping does not destroy the antiferromagnetic order in the system, it induces an increase in the staggered magnetic moment. These results suggest that the Tl0.4K0.4Fe2−y Se2 system is a system with intrinsic phase separation. The change in the valence state of Fe could be a possible reason for the suppression of superconductivity.

The substitution of Ga for Mn in manganite Nd0.6Dy0.1Sr0.3MnO3 with a ferromagnetic (FM) ground state has been performed to study the influence of the Mn-sublattice magnetic ordering on the magnetic rare-earth sublattice. It is found that the substitution of Mn3+ with Ga3+ ions results in a sharp decrease of TC, reflecting the reduction of the double-exchange interactions strength JMn–Mn. At the same time, a depinning effect of the rare-earth magnetic moment has been observed. This behavior unambiguously proves that the exchange interaction between Mn and rare-earth ions JMn–R strongly influences the rare-earth magnetic ordering at temperatures below TC and stabilizes the rare-earth magnetic ground state.

In this paper, we have studied the magnetic and magnetocaloric properties of the perovskite manganite Pr 0.55 Sr 0.45 MnO 3 . It shows a sharp paramagnetic–ferromagnetic phase transition at 291 K and possesses a moderate magnetic entropy change near room temperature. In addition, a large relative cooling power (143.64 J/kg) and a wide temperature range (84 K) have been found in this material. Compare with the Landau model, we find that the itinerant electrons mainly contribute the larger magnetic entropy change at paramagnetic region.

The epitaxial thin films of Ge0.96−xBixFe0.04Te are deposited on BaF2 substrates by using pulsed laser deposition technique. The thin films with three different compositions i.e. Ge0.8Bi0.2Te, Ge0.76Bi0.2Fe0.04Te, and Ge0.64Bi0.32Fe0.04Te are prepared in this wok. Their high-quality epitaxy and crystallinity are confirmed by X-ray diffraction and atomic force microscopy. According to the measurements of Hall effect variation, we find that each of all curves exhibits a negative slope for the different films as the temperature varies from low temperature to room temperature, indicating that Ge0.96−xBixFe0.04Te films are n-type material because the substitution of Bi for Ge makes the carriers change from holes into electrons. Temperature dependence of resistivity confirms that the electronic transport behavior for each of Ge0.96−xBixFe0.04Te thin films exhibits a typical semiconductor characteristic. From the measurements of temperature dependence of electronic transport under various external magnetic fields, we find that the Ge0.64Bi0.32Fe0.04Te thin film shows some magnetoresistive effect while other composition films do not possess such a property. Based on the linear fitting of temperature dependence of magnetic susceptibility in high temperature and low temperature region, the magnetic property of Ge0.64Bi0.32Fe0.04Te thin film changes from 253 K. Together with the study of magnetic susceptibility curve in the paramagnetic region, the Curie-Weiss temperature is determined to be 102 K. At a low temperature of 10.0 K, we observe an obvious ferromagnetic hystersis loop in Ge0.64Bi0.32Fe0.04Te instead of in Ge0.76Bi0.2Fe0.04Te thin film. These results imply that the increase of Bi dopant is main reason for the establishment of ferromagnetic ordering state. The carrier concentration increases and thus promotes the carriers transporting the Ruderman-Kittel-Kasuya-Yoshida interaction, thereby leading to the separated Fe ions producing the magnetic interaction and forming an n-type diluted magnetic semiconductor.

The lattice dynamics in the CuIr2S4 system have been investigated through Raman spectroscopy and the induced-pressure effect. Four Raman active modes are observed experimentally. Upon cooling, these Raman spectra undergo changes due to the Peierls-like phase transition. In addition, the substitution of Ag for Cu affects the amplitude of the Raman spectra while keeping their wave number unchanged. Furthermore, the positive and negative pressure effects are induced by shrinking and expanding the lattice. It is suggested that the pressure effect is an effective proof of the orbital-induced Peierls state mechanism.

We report electrical transport and anisotropic magnetic properties of Mn-intercalated 2H-TaS2, a layered transition-metal dichalcogenide with a hexagonal structure. The single crystal MnxTaS2 with x = 1/3 exhibits a transition from paramagnetism to ferromagnetism near 70 K, below which both the magnetoresistance and magnetization properties present strong anisotropic behavior. Its anisotropic magnetoresistance effect and in-plane soft ferromagnetic property suggests that this layered material would be a good candidate for exploring the physics of two-dimensional ferromagnetism.

In the present work, the magnetic entropy change of the half-doped Nd0.5Ca0.25Sr0.25MnO3 manganite has been investigated. The measurement of isothermal magnetization around Curie temperature reveals the maximum isothermal magnetic entropy change of 1.85 and 0.77 J/kg K for Δ H = 3.0 and 1.0 T magnetic field variation, respectively. In addition, from the data of heat capacity, we find the adiabatic temperature change of 0.88 K for a magnetic field variation of 3.0 T. Though only a moderate magnetic entropy change and a small adiabatic temperature change were obtained, a considerable large relative cooling power (140 J/kg as Δ H = 3.0 T ) and a wide temperature range (74 K as Δ H = 3.0 T ) were found in this sample, this ensure it to be a promising candidate for the actual magnetic refrigerant materials.

We perform oxygen doping experiments in the CaFeAsF and CaFe0.88Co0.12AsF compounds. In the parent compound CaFeAsF, partial replacement of F by O leads to an increase of resistivity and a weakening of spin-density wave transition, indicating that the out-of-plane disorder strongly affects the electronic and magnetic properties of the system. In the CaFe0.88Co0.12AsF1−xOx system, the doping of oxygen leads to the suppression of superconductivity, reflecting the importance of Ca–F layer disorder in this system.

In this paper, the magnetocaloric effect of perovskite manganite Nd 0.6 La 0.1 Sr 0.3 MnO 3 has been investigated. From the measurement of isothermal magnetization around the Curie temperature, we have calculated the maximum isothermal magnetic entropy change as 3.14 J/kg K for the 1.5 T magnetic field variation. Furthermore, a large relative cooling power of 45 J/kg has been determined, which makes Nd 0.6 La 0.1 Sr 0.3 MnO 3 attractive candidate materials for magnetic refrigeration.

Charge density wave (CDW), the periodic modulation of the electronic charge density, will open a gap on the Fermi surface that commonly leads to decreased or vanishing conductivity. On the other hand superconductivity, a commonly believed competing order, features a Fermi surface gap that results in infinite conductivity. Here we report that superconductivity emerges upon Se doping in CDW conductor ZrTe$_{3}$ when the long range CDW order is gradually suppressed. Superconducting critical temperature $T_c(x)$ in ZrTe$_{3-x}$Se$_x$ (${0\leq}x\leq0.1$) increases up to 4 K plateau for $0.04$$\leq$$x$$\leq$$0.07$. Further increase in Se content results in diminishing $T_{c}$ and filametary superconductivity. The CDW modes from Raman spectra are observed in $x$ = 0.04 and 0.1 crystals, where signature of ZrTe$_{3}$ CDW order in resistivity vanishes. The electronic-scattering for high $T_{c}$ crystals is dominated by local CDW fluctuations at high temperures, the resistivity is linear up to highest measured $T=300K$ and contributes to substantial in-plane anisotropy., Comment: 15 pages, 4 figures

In this paper, magnetic field and hydrostatic pressure effects on magnetism of ZnCr2S4 were investigated. Upon cooling the sample at 0.5 T to 2 K then warming back, the magnetization displays irreversibility between the cooling and warming sequence at temperatures around incommensurate–commensurate antiferromagnetic transition TN2. With increasing magnetic field or hydrostatic pressure, the irreversibility is gradually suppressed, although the thermal hysteresis is shifted to higher temperatures under pressure. The observed thermal hysteresis is attributed to a structural transition and evolution of different magnetic phases upon cooling and warming.

Spin-lattice coupling plays an important role in both formation and understanding of the magnetism in two-dimensional magnetic semiconductors (2DMS). In this paper, the steady pressure effects on the lattice structure, Raman resonances, and magnetization of a 2DMS Cr2Ge2Te6 have been studied by both experiments and first principles calculations. It is found that the bond length of Cr-Cr decreases, the angle of Cr-Te-Cr diverges from 90°, and the Raman modes Eg3 and Ag1 show an increase with the application of external pressure. Consequently, the magnetic phase transition temperature TC decreases from 66.6 K to 60.6 K (∼9%) as the pressure increases from 0 to 1 GPa. These pressure effects not only confirm the existence of strong spin-lattice coupling but also reveal the detailed information about the lattice deformation effect on the magnetic properties in such 2DMS, which would be a benefit for the further understanding and manipulation of the magnetism in 2D materials.

The planar Hall effect (PHE) in a ruthenate Sr4Ru3O10 nanosheet as a function of the magnetic field direction and temperature has been investigated. From the magnetic reversal induced PHE signal, we find that the [ 1 ¯ 10] direction is the in-plane ferromagnetic easy-axis and the [110] direction is a metastable magnetic axis of the Sr4Ru3O10 nanosheet. This in-plane magnetic anisotropy can lead to a large, measurable, and field direction sensitive resistance switching when an in-plane magnetic field is swept, suggesting that Sr4Ru3O10 may have potential applications in spintronic and magnetic sensor devices.

We report here an enhanced magnetoelectric effect in a Y-type hexaferrite Ba0.5Sr1.5Zn2Fe12O22 with Fe3+ ions partially substituted by magnetic Cr3+ ions (i.e., BSZFCO). The direct magnetoelectric effect is persistent up to 250 K, with the maximal susceptibility of ∼1309 ps/m at 75 K. More importantly, the pronounced non-zero electric polarization at zero magnetic field and four magnetoelectric states induced by different initial poling fields make it quite unique to serve in a magnetoelectric device. The stability of the direct (inverse) magnetoelectric effect is confirmed by the nonvolatile behavior in response to the cyclically sweeping magnetic (electric) fields. Our studies provide an insight into the nontrivial properties of BSZFCO, which are promising for multiferroic applications.

We report the discovery of superconductivity at $\ensuremath{\sim}9$ K in Fe${}_{1.05}$Te single crystals that have been exposed to air for more than six months. The superconductivity is induced due to the oxygen incorporation and only exists in the surface layer of the samples. Our high-resolution transmission electron microscopy experiments and density functional theory calculations show the oxygen prefers to locate at the interstitial site in the Fe-Te layer. X-ray photoelectron spectra characterize an enhancement of the itinerant character of Fe $3d$ electrons, which may reduce the local moment and hence suppress the long-range antiferromagnetism associated with superexchange interactions. This work suggests the bicollinear antiferromagnetism in Fe${}_{1+y}$Te can be suppressed by oxygen incorporation to induce superconductivity and thus could be considered as the parent phase of the superconductivity.

Oxygen vacancies (V(O)) effects on magnetic ordering in Eu₀.₅Ba₀.₅TiO₃₋δ (EBTO₃₋δ) thin films have been investigated using a combination of experimental measurements and first-principles density-functional calculations. Two kinds of EBTO₃₋δ thin films with different oxygen deficiency have been fabricated. A nuclear resonance backscattering spectrometry technique has been used to quantitatively measure contents of the V(O). Eu₀.₅Ba₀.₅TiO₃ ceramics have been known to exhibit ferroelectric (FE) and G-type antiferromagnetic (AFM) properties. While, a ferromagnetic (FM) behavior with a Curie temperature of 1.85 K has been found in the EBTO₃₋δ thin films. Spin-polarized Ti(3+) ions, which originated from the V(O), has been proven to mediate a FM coupling between the local Eu 4f spins and were believed to be responsible for the great change of the magnetic ordering. Considering the easy formation of V(O), our work opens up a new avenue for achieving co-existence of FM and FE orders in oxide materials.

In this work, we investigate the local structural distortion of the double perovskite Ba$_2$YMoO$_6$ by means of infrared transmission spectroscopy. At 300 K, three bands are observed at $\sim$ 255.1 cm$^{-1}$, $\sim$ 343.4 cm$^{-1}$, and $\sim$ 561.5 cm$^{-1}$, which are related to the motion between the cation Ba$^{2+}$ and the anion YMO$_6^{-2}$, the Y-O stretching motion and the stretching vibration of the MoO$_6$ octahedron, respectively. These modes continue to harden upon cooling owing to the shrink of the lattice constant. When the temperature decreases to $T \leq$ 130 K around which the spin singlet dimer begins to form, an additional phonon mode appears at $\sim$ 611 cm$^{-1}$, suggesting the occurrence of local distortion of MoO$_6$ octahedra. With further decrease of the temperature, its intensity enhances and its peak position keeps unchanged. These results indicate that the formation of the spin singlet dimers is accompanied with the occurrence of the local structure distortion of MoO$_6$ octahedra, providing evidence for the strong spin-phonon coupling in the double perovskite Ba$_2$YMoO$_6$., Comment: 3 pages, 3 figures, accepted for publication in J. Appl. Phys. (Proceedings of the 12th Joint MMM/Intermag Conference)

HgCr2S4 is a typical compound manifesting competing ferromagnetic (FM) and antiferromagnetic (AFM) exchanges as well as strong spin-lattice coupling. Here we study these effects by intentionally choosing a combination of magnetization under external hydrostatic pressure and thermal conductivity at various magnetic fields. Upon applying pressure up to 10 kbar at 1 kOe, while the magnitude of magnetization reduces progressively, the AFM ordering temperature TN enhances concomitantly at a rate of about 1.5 K/kbar. Strikingly, at 10 kOe the field polarized FM state is found to be driven readily back to an AFM one even at only 5 kbar. In addition, the thermal conductivity exhibits drastic increments at various fields in the temperature range with strong spin fluctuations, reaching about 30% at 50 kOe. Consequently, the results give new experimental evidence of spin-lattice coupling. Apart from the colossal magnetocapacitance and colossal magnetoresistance reported previously, the findings here may enable new promising functionalities for potential applications.

The electronic doping effect on both the superconductivity and the nematic order in the FeSe nanoflake are investigated by using the electric-double-layer transistor configuration. The superconductivity can be effectively controlled by electronic doping, and the onset superconducting transition temperature Tc reaches as high as 45 K at a gate voltage of Vg = 4 V. Meanwhile, the nematic phase is gradually suppressed with the increase of electronic doping (or Vg). The results provide an effective method with variable charge doping for investigation of the rich physics in the FeSe superconductor.