Isothermal Magnetization Curves Research Articles

Critical behavior of the ferromagnetic metal La3CrAs5 with quasi-one-dimensional spin chains

In this work, we report on the critical properties of ferromagnetic metal La3CrAs5, where the face-sharing CrAs6 octahedral chains are separated by a large distance. Bulk magnetization measurements near the Curie temperature TC are carried out in details. Then we used modified Arrott plot, Kouvel-Fisher method and critical isotherm analysis to analyze the isothermal magnetization curves, and thus obtained a set of precise and self-consistent critical exponents (β, γ and δ), which are close to the theoretical values of chiral XY model. In addition, the scaling equation is followed by the magnetization-field-temperature curves, confirming the reliability of these critical exponents. Furthermore, the magnetic exchange distance, decaying as J(r) ~ r−4.7, indicates the predominant long-range magnetic coupling in La3CrAs5. Furthermore, the magnetic entropy change − ΔSM around the TC reaches a maximum value, such as−ΔSMmax is 1.23 J/kg-K for H = 50 kOe, and the relative cooling power (RCP) is 51.70 J/kg at H = 50 kOe. Our results reveal that the magnetic critical behavior in La3CrAs5 should be attributed to the synergistic action between the direct magnetic exchange and the itinerant electron mediated indirect spin exchange, and the interchain spin coupling should be greatly enhanced via the itinerant electrons and then leads to the increase of the long-range magnetic ordering temperature.

Transformation of magnetic ordering in MnCo1-xNixGe (x = 0–0.6) alloys, its investigations on structural, transport, magnetic, and magnetocaloric properties

In the latest study, physical behaviour of (structure, transport, magnetism, and magnetocaloric effect, critical exponents studies) MnCo1-xNixGe (x = 0, 0.2, 0.4, 0.6) intermetallic alloys are enquired. The parental MnCoGe reveals doublet-orthorhombic at ambient temperature, while doping up Ni crystallographic structure is renovated from the mixed-phase of Orthorhombic-Hexagonal to complete hexagonally crystallized by confirmation of high-temperature XRD. From the transport measurements, Semiconductor (x = 0.2) to metallic (x = 0.4, 0.6) transitions are appeared. The suppression of magneto-structural transitions (MST’s), First [(AFM-FM)-(TM)] to Second [(FM-PM)-(TCA)] order transformation are recognized from thermo-magnetic measurements [M (T)]. The presence and absence of Field-Induced Meta Magnetic Transitions (FIMMT) for parent (x = 0) and doped (x = 0.2, 0.4, 0.6) samples have appeared from isothermal magnetization curves [M (H)]. Giant MCE is perceived near RT (303 K) for x = 0 and decreases for Ni-doped samples by dropping temperatures. The change in magnetic entropy (ΔSM) decreases with increasing Ni substitution. Refrigeration capacity (RC) linearly increases with magnetic field for all samples and decreases with Ni compositions.

ПЕРІОДИЧНІСТЬ ЗЕМЛЕТРУСІВ У КАСПІЙСЬКОМУ МОРІ

Magnetic minerals form or alter in the presence of hydrocarbons, making them a potential magnetic proxy for identifying hydrocarbon migration pathways. We concentrate in the precision magnetic mineralogical analyzes to understand what magnetic minerals in soil from the hydrocarbon fields are responsible for the magnetic signal. To illustrate the results of our studying, we consider the study area of the hydrocarbon deposits near the village Balabanivka, Bogodukhiv district, Kharkiv region. A collection of soil samples is represented by deep medium-humus chernozems. The thermomagnetic analyzes, hysteresis parameters, and isothermal remanent magnetization curves (IRM) were studied for the samples collected near the well (point PR 28) and at the area located out of the hydrocarbon influence zone (point PR 0403). To study the thermomagnetic parameters, different types of the magnetization and magnetic susceptibility (MS, χ), and hysteresis loops we used the Variable Field Translation Balance (VFTB) instrument. The results are confirmed by the highest values of the gas geochemical parameters. The MS variations at temperatures ranging from 200 to 400 ˚C may reflect the presence of either iron sulphides or maghemite. The magnetite occurs for all soils. The wasp-waisted hysteresis loops identified either a mixture of two magnetic minerals (magnetite and hematite) and the admixture of the superparamagnetic and larger grains of the same minerals.

Magnetic and anisotropic magnetocaloric effects of HoCoSi fast quenching ribbons

The performance of magnetocaloric effect materials is one of the key factors restricting the development of magnetic refrigeration technology. Materials with anisotropic magnetocaloric effect can be used in the rotary magnetic refrigeration technology, which is beneficial to the simplification of refrigeration devices. In this work, the magnetic properties, magnetocaloric effects, and magnetic anisotropies of rapidly quenched HoCoSi compounds are investigated. At low temperatures below <i>T</i><sub>t</sub> = 5.7 K, the HoCoSi ferromagnetism and helical magnetism coexist. With the increase of temperature, the HoCoSi undergoes a second-order phase transition from ferromagnetic (FM) to paramagnetic (PM) phase at <i>T</i><sub>C</sub> = 13.7 K. Both XRD and SEM show that the HoCoSi has a preferred orientation. In order to obtain a large magnetocaloric effect and to determine the effect of preferred orientation on magnetism and magnetocaloric effect, the isothermal magnetization curves of the 10 m/s–HoCoSi fast quenched belt in the directions of <i>H</i> parallel and perpendicular to texture around the Curie temperature are analyzed. The corresponding magnetic entropy change (–Δ<i>S</i><sub>M</sub>) and magnetic refrigeration capacity (RC) are calculated. Under the magnetic field changing from 0 to 5 T, the value of –Δ<i>S</i><sub>M</sub> is 22 J/(kg·K) in the direction of <i>H</i> parallel to the texture and 12 J/(kg·K) in the direction of <i>H</i> perpendicular to texture , and their corresponding values of RC(RCP)are 360 (393.8) J·kg<sup>–1</sup> and 160 (254.4) J/kg. The value of –Δ<i>S</i><sub>M</sub> reaches 12.5 J/(kg·K)even at <i>μ</i><sub>0</sub><i>H</i> = 0–2 T in the direction of H parallel to the texture. It is obvious that the 10-m/s-HoCoSi fast quenching belt shows a large low-field magnetocaloric effect and obvious magnetic anisotropy, which is expected to be used to realize the magnetic refrigeration technology of rotating samples.

Vortex phase diagram in 1111-type CaFe0.89Co0.11AsF single crystal

Studying the vortex properties in high-T c superconductors is crucial for understanding the high-temperature superconducting mechanism. However, until now, only a few vortex studies have been performed in 1111-type iron-based superconductors due to their smaller-sized single crystals. In this study, we have synthesized millimeter-sized CaFe0.89Co0.11AsF single crystals by the self-flux method. A three-dimensional vortex nature was confirmed in the thermally activated flux flow region. Second, a magnetization peak was observed on the isothermal magnetization curves. Meanwhile, the dominant role of normal point pinning was also confirmed. Finally, the various phase boundaries of the vortex were determined based on an analysis of the resistivity and magnetization data, and a complete vortex phase diagram of CaFe0.89Co0.11AsF single crystals was established.

Observation of exchange-bias in the inverse Heusler alloy Mn1.5Ru1.5Si

Recently, Mn-Ru-Ga based inverse Heusler alloys have been found to be potential candidates for half-metallic fully compensated ferrimagnetic materials. In this work, we have studied another Heusler based alloy, Mn1:5Ru1:5Si, intending to design a compensated ferrimagnet. The alloy Mn1:5Ru1:5Si crystallizes in an inverse Heusler (XA) structure with a small amount of anti-site disorder. Our magnetic study indicates that the alloy orders magnetically below about TN = 50 K, which is characterized by a sharp drop in magnetization. Nevertheless, the isothermal magnetization curve shows a tendency of saturation and finite coercivity at 5 K, which rules out a pure antiferromagnetic state. Interestingly, Mn1:5Ru1:5Si shows vanishingly small magnetic moment, which also rules out possibility of a pure antiferromagnetic state. The alloy shows a significant amount of exchange-bias at low temperature. The alloy fails to obey a Curie-Weiss law between 300 and 50 K, indicating short-range correlations prior to the long-range order at TN. The exchange bias possible arises from the interfacial coupling of the short range ferromagnetic clusters with the long range antiferromagnetic state. The observation of exchange bias for such a system along with a low net magnetization value, has immense potential for magneto-electric applications and switching devices. The resistivity versus temperature data of the sample indicates a metallic character, albeit with a rather large value resistivity. The resistivity data show an upturn below 25 K that follows a logarithmic behaviour. Such upturn may be due to weak localization effect due to the presence of antisite disorder and short range magnetic clusters.

Optical and Magnetic Properties of Cubic Double Perovskites Ba2RSbO6(R= Dy, Gd) Coordinated to Lattice Dynamical and Crystal‐Field Computations

Herein, optical (e.g., UV–Vis reflectance spectra, infrared and Raman spectroscopy) and magnetization properties of the double‐perovskite compounds Ba2DySbO6(BDS) and Ba2GdSbO6(BGS) are reported. Optical bandgap is determined to be 4.524 eV for BDS and 4.465 eV for BGS using Kubelka–Munk function fit to the UV–Vis spectra. The lattice dynamical calculations on the force‐field model are undertaken for assigning the observed infrared and Raman modes. The dc susceptibility does not exhibit magnetic ordering down to 2 K for the two compounds. The dc magnetization atT = 2 K does not saturate for BDS even at a magnetic field of 11 T, but saturates at 5 T to a value of 7μB/Gd3+for BGS. A frequency‐dependent cusp in the ac susceptibility appears at 3.3 K, that is unlikely generic spin‐glass‐like freezing, and may be attributed to the short‐range correlations among Dy3+‐moments in BDS. Crystal‐field (CF) computations are performed to analyze the magnetic data for BDS. The obtained CF level scheme of Dy3+ions demonstrates the observed susceptibility and isothermal magnetization curves very well. The field‐dependence of the two lowest CF levels along different principal axes does not exhibit any level crossing, consistent with the lack of ordering in Ba2DySbO6.

Magnetic properties of the quasi two-dimensional centered honeycomb antiferromagnet GdInO3

The crystal structure and magnetic property of the single crystalline hexagonal rare-earth indium oxides ${\mathrm{GdInO}}_{3}$ have been studied by combing experiments and model calculations. The two inequivalent ${\mathrm{Gd}}^{3+}$ ions form the centered honeycomb lattice, which consists of honeycomb and triangular sublattices. The dc magnetic susceptibility and specific heat measurements suggest two antiferromagnetic phase transitions at ${T}_{\text{N1}}=2.3\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ and ${T}_{\text{N2}}=1.02\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. An inflection point is observed in the isothermal magnetization curve, which can be an indication of an up-up-down phase with a 1/3 magnetization plateau, further supported by our theoretical calculation. We also observe a large magnetic entropy change originated from the magnetic frustration in ${\mathrm{GdInO}}_{3}$. By considering a classical spin Hamiltonian, we establish the ground state phase diagram, which suggests that ${\mathrm{GdInO}}_{3}$ has a weak easy-axis anisotropy and is close to the equilateral triangular-lattice system. The theoretical ground-state phase diagram may be used as a reference in NMR, ESR, or $\ensuremath{\mu}\mathrm{SR}$ experiments in future.

Magnetic and Magnetocaloric Properties of Pr₂Fe<SUB>17-x</SUB>Cu<SUB>x</SUB> Intermetallic Compounds

In this study, Cu-doped intermetallic compounds with the chemical composition of Pr₂FeSUB17-x/SUBCuSUBx/SUB (x = 0, 0.1, 0.2) were prepared by the arc-melting process. SEM analysis revealed that the samples consist of irregularly shaped and strongly connected micron-scale particles range from 0.5 μm to 4 μm. EDX analysis showed that all the samples consist of a single phase. The magnetic measurements revealed that all the samples exhibit a ferromagnetic to the paramagnetic phase transition. The Curie temperature was determined to increase linearly with increasing Cu substitution from 286 K for x = 0 to 303 K for x = 0.2. The maximum value of magnetic entropy change |ΔSm| was estimated from isothermal magnetization curves and it decreases with increasing Cu content from 5.63 J/kg·K for x = 0 to 4.21 J/kg·K for x = 0.2 at 5 T magnetic field change. At the same magnetic field change, the relative cooling power values range from 404.8 J/Kg for x = 0 to 248.3 J/Kg for x = 0.2. Arrott plots and Landau analyses revealed that all the samples show second-order magnetic phase transition.

Magnetic and electrical properties by Ca2+ doping in SmCrO3 orthochromites

Spectroscopic (UV–vis and XPS) magnetic and electrical properties of the Ca2+ doped SmCrO3 system were phenomenologically investigated. The Cr3+, Cr5+, and Cr6+ species were identified by XPS spectroscopy in Sm1−xCaxCrO3 (0 ≤ x ≤ 0.20). Rietveld analyses of the X-ray diffraction data reveal a smooth decrease in the cel`l parameters assigned to the Cr6+ formation as a function of the Ca2+ content. Diffuse reflectance spectroscopy showed that the wider optical bandgap of the system corresponds to a charge transfer process, and it disappears for x ≥ 0.1, showing t2 g-eg electronic gaps. The electrical measurements were fitted in two temperature ranges; for low temperatures (85–150 K), a 3D variable-range hopping mechanism seems to prevail, while for the 150–300 K range, the electrical behavior is well represented by the small-polarons conduction mechanism. Magnetic properties of Sm1−xCaxCrO3 were highly sensitive to the Ca2+ content, and the TN values varied from 192 to 151 K for x = 0 and x = 0.20, respectively; TRS varied from 34 to 9 K for the same x values. Isothermal magnetization curves at 5 K suggest that, as a function of the Ca2+ content, the Γ4 ferromagnetic phase remains for x ≥ 0.04; while for x = 0 and x = 0.02, the Γ2 ferromagnetic phase is the only one observed.

Investigation on X-ray photoelectron spectroscopy, structural and low temperature magnetic properties of Ni-Ti co-substituted M-type strontium hexaferrites prepared by ball milling technique

The effect of substituting Fe3+ ions by a combination of divalent Ni2+ and tetravalent Ti4+ in SrM hexaferrites synthesized by mechanical ball-milling technique were reported. Standard SrFe12O19 hexagonal ferrite (P63/mmc) was confirmed by measured XRD patterns. The phase purity was also confirmed by the XPS. The SEM images showed a clear hexagonal-shape particles in the prepared ferrites. The elemental distribution obtained from EDX spectra for SrFe12–2xNixTixO19 (x = 0.2, 0.4, 0.6 and 0.8) was consistent with stoichiometry of the starting powder. X-ray photoelectron spectra confirmed the existence of Fe2+, Fe3+, Ni2+, Ni3+ and Ti4+ ions. The presence of Fe2+ and Ni3+ was correlated with an electron transfer between Fe3+ and Ni2+. By increasing the Ni concentration, we found that some Fe3+ ions are transferred to Fe2+ ions, while some of the Ni2+ ions are transferred to Ni3+ ions. Irreversible ZFC and FC curves were recorded in the 4–300 K temperature range. The isothermal magnetization curves confirmed the ferromagnetic behavior for all synthesized samples. A small variation in the saturation and remnant magnetizations along with a sharp reduction in the coercivity fields with the increase of x were observed in a wide range of temperatures. The broad peak observed in the temperature dependence of the saturation magnetization for x = 0.8 may be referred to the spin reorientation transition. The decrease in the coercivity agrees with the behaviour of the magneto crystalline anisotropy while the first anisotropy constant exhibits a fast decrease above x = 0.6.

Magnetic structure, excitations and short-range order in honeycomb Na2Ni2TeO6

Na2Ni2TeO6 has a layered hexagonal structure with a honeycomb lattice constituted by Ni2+ and a chiral charge distribution of Na+ that resides between the Ni layers. In the present work, the antiferromagnetic (AFM) transition temperature of Na2Ni2TeO6 is confirmed at T N ≈ 27 K, and further, it is found to be robust up to 8 T magnetic field and 1.2 GPa external pressure; and, without any frequency-dependence. Slight deviations from nominal Na-content (up to 5%) does not seem to influence the magnetic transition temperature, T N. Isothermal magnetization curves remain almost linear up to 13 T. Our analysis of neutron diffraction data shows that the magnetic structure of Na2Ni2TeO6 is faithfully described by a model consisting of two phases described by the commensurate wave vectors , and , with an additional short-range order component incorporated in to the latter phase. Consequently, a zig-zag long-range ordered magnetic phase of Ni2+ results in the compound, mixed with a short-range ordered phase, which is supported by our specific heat data. Theoretical computations based on density functional theory predict predominantly in-plane magnetic exchange interactions that conform to a J 1–J 2–J 3 model with a strong J 3 term. The computationally predicted parameters lead to a reliable estimate for T N and the experimentally observed zig-zag magnetic structure. A spin wave excitation in Na2Ni2TeO6 at E ≈ 5 meV at T = 5 K is mapped out through inelastic neutron scattering experiments, which is reproduced by linear spin wave theory calculations using the J values from our computations. Our specific heat data and inelastic neutron scattering data strongly indicate the presence of short-range spin correlations, at T > T N, stemming from incipient AFM clusters.

Magnetic properties and Cluster-glass phenomena in 1-D spin chain compound [formula omitted

We report the structural and magnetic properties of Ca3-xDyxCo2O6 (x = 0, 0.1, 0.2, and 0.3). We found evidence of Cluster-glass (CG)-like freezing phenomena in these samples. The isothermal magnetization curve depicts step-like change indicative of the first-order transition, which decreases with the increase of substitution. The Brillouin function was used to determine the ‘spins’, participating at this first-order transition J12→J32. Relaxation measurements revealed the existence of short-range Cluster-glass-like behavior. Analyzing the results using Vogel-Fulcher law shows that the Vogel-Fulcher temperature (T0) and the relaxation time is around 10 K and 104 s, respectively.

Magnetoelastic transition and giant anisotropic magnetostriction effect in textured Mn<sub>1.9</sub>Co<sub>0.1</sub>Sb polycrystal

Mn2Sb-based alloys have extremely promising practical applications in many fields owing to their abundant and controllable magnetofuntional properties around the first-order magnetoelastic transition, as well as their low costs. However, only a few studies on the magnetostrain of these alloys have been reported. Herein, a highly textured Mn1.9Co0.1Sb polycrystal is fabricated by using the arc-melting technique, which produces a strong temperature gradient induced by rapid cooling during the arc-melting process, resulting in the highly selective orientation of crystal growth. X-ray diffraction and thermomagnetic measurements show that the grains grow in certain crystallographic directions. Metamagnetic transition is revealed by the isothermal magnetization curve measurements, which is observed to be more obvious at lower temperatures. The standard resistive strain-gauge method is adopted to measure the magnetostriction effect. Giant anisotropic magnetostrain values of up to 0.246% and −0.11% are obtained parallel and vertical to the texture of the alloy, respectively. This magnetostriction effect mainly originates from the anisotropic lattice distortion across the first-order magnetoelastic phase transition.

Magnetic Properties of a Holocene Sediment Core from the Yeongsan Estuary, Southwest Korea: Implications for Diagenetic Effects and Availability as Paleoenvironmental Proxies

The sensitivity of magnetic properties, which characterize the mineralogy, concentration, and grain size distribution of magnetic minerals, to environmental processes may provide useful information on paleoenvironmental changes in estuarine environments. Magnetic property studies of estuaries are less common than other environments and, due to the west coast of South Korea having an abundance of estuaries, it provides a good place to study these processes. In this study, we analyzed a variety of magnetic properties based on magnetic susceptibility, hysteresis parameters, progressive acquisition of isothermal remanent magnetization and first-order reversal curve data from a Holocene muddy sediment core recovered from the Yeongsan Estuary on the west coast of South Korea. We examined diagenetic effects on magnetic properties and tested their availability as proxies of paleoenvironmental change. The presence of generally low magnetic susceptibility, ubiquitous greigite-like authigenic magnetic component, and very fine magnetic particle occurrence suggested that the analyzed sediments had undergone considerable early diagenetic alteration. Electron microscopic observations of magnetic minerals support this suggestion. Our results confirm that the use of initial bulk susceptibility as a stand-alone environmental change proxy is not recommended unless it is supported by additional magnetic analyses. We recognized the existence of ferromagnetic-based variabilities related to something besides the adverse diagenetic effects, and have examined possible relationships with sea-level and major climate changes during the Holocene. The most remarkable finding of this study is the two distinct intervals with high values in magnetic coercivity (Bc), coercivity of remanence (Bcr), and ratio of remanent saturation moment to saturation moment (Mrs/Ms) that were well coincident with the respective abrupt decelerations in the rate of sea-level rise occurred at around 8.2 and 7 thousand years ago. It is then inferred that such condition with abrupt drop in sea-level rise rate would be favorable for the abrupt modification of grain size distribution toward more single-domain-like content. We modestly propose consideration of the Bc, Bcr, and Mrs/Ms variability as a potential indicator for the initiation/occurrence of sea-level stillstand/slowstand or highstand during the Holocence, at least at estuarine environments in and around the studied area.

Effect of chromium substitution on structural, magnetic and magnetocaloric properties of GdFe12−xCrx intermetallic compounds, Mössbauer spectrometry and ab initio calculations

The single-phase intermetallic compounds GdFe12−xCrx (x ​= ​2, 2.5 and 3), elaborated by arc-melting method and annealed at 1073 ​K, crystallize in the ThMn12-type structure with the I4/mmm space group. The structural, magnetic and magnetocaloric properties of these intermetallic compounds were studied extensively by means of X-ray powder diffraction (XRD), Mössbauer spectrometry and magnetic measurements. The Rietveld analysis of X-ray diffraction patterns reveals that the lattice parameters of GdFe12−xCrx (x ​= ​2, 2.5 and 3) compounds increase linearly with increasing Cr content up to x ​= ​3, and proves that Cr atom prefers 8i sites in the ThMn12 structure and that Fe occupies 8i, 8f and 8j. The Mössbauer spectra study based on the Wigner-Seitz cell volumes correlation with the isomer shift parameter of each specific site 8i, 8f and 8j, confirms the preferred inequivalent crystallographic site of Cr atoms. Ab initio calculations of GdFe12−xCrx were performed using the density functional theory (DFT) based on the full potential linearized augmented plane wave (FLAPW). The calculated data are in good agreement with the results of the magnetic measurements as well as with the Mössbauer spectrometry. The variation of magnetization (M) vs. temperature (T) reveals that all compounds exhibit a second-order ferromagnetic to paramagnetic phase transition in the vicinity of the Curie temperature (TC). The substitution of Fe by Cr yields enhancement of the magnetic ordering transition temperature. The maximum magnetic entropy change (ΔSM) was estimated from isothermal magnetization curves and it increases from 1.82 ​J/kg.K for x ​= ​2, to 2.95 ​J/kg.K for x ​= ​3, under a field change of 1.5 ​T. The relative cooling power (RCP) is in the range of 12.5 ​J/kg for x ​= ​2 and 30.4 ​J/kg for x ​= ​3. Our results suggest that such substituted compounds could be considered as a potential candidate for magnetic refrigeration technology.

Assessment of Magnetic Techniques for Understanding Complex Mixtures of Magnetite and Hematite: The Inuyama Red Chert

AbstractMagnetite and hematite mixtures occur widely in nature. Magnetic unmixing of the signals recorded by these minerals can be important for assessing the origin of their respective paleomagnetic remanences and for extracting geological and paleoenvironmental information. However, unmixing magnetic signals from complex magnetite and hematite mixtures is difficult because of the weak magnetization and high coercivity of hematite. We assess here the relative effectiveness of first‐order reversal curve (FORC) and extended FORC‐type diagrams, FORC‐principal component analysis (PCA), isothermal remanent magnetization (IRM) curve decomposition, and PCA of remanent hysteretic curves for unmixing magnetic components in samples from the magnetically complex Inuyama red chert, Japan. We also further characterize the domain state and coercivity distributions of both magnetite and hematite with FORC‐PCA and IRM acquisition analysis in the red chert. We show that IRM curve decomposition can provide valuable component‐specific information linked to coercivity, while FORC‐PCA enables effective magnetic domain state identification. PCA of remanent hysteretic curves provides useful information about the most significant factors influencing remanence variations and subtle coercivity changes. To identify components in complex magnetite and hematite mixtures, we recommend PCA analysis of remanent hysteretic curves combined with FORC analysis of representative samples to identify domain states and coercivity distributions.

High-Pressure Synthesis of Double Perovskite Ba2NiIrO6: In Search of a Ferromagnetic Insulator.

Double perovskite oxides with d8-d3 electronic configurations are expected to be ferromagnetic from the Goodenough-Kanamori rules, such as ferromagnetic La2NiMnO6. In search of new ferromagnetic insulators, double perovskite Ba2NiIrO6 was successfully synthesized by high-pressure and high-temperature methods (8 GPa and 1573 K). Ba2NiIrO6 crystallizes in a cubic double perovskite structure (space group: Fm3̅m), with an ordered arrangement of NiO6 and IrO6 octahedra. X-ray absorption near-edge spectroscopy confirms the nominal Ni(II) and Ir(VI) valence states. Ba2NiIrO6 displays an antiferromagnetic order at 51 K. The positive Weiss temperature, however, indicates that ferromagnetic interactions are dominant. Isothermal magnetization curves at low temperatures support a field-induced spin-flop transition.

Zero-field ferroelectric state and magnetoelectric coupling in antiferromagnetic Fe4Nb2O9 single crystal

High quality Fe4Nb2O9 single crystal was grown by optical floating zone method. The magnetization-temperature(M-T) curves, isothermal magnetization curves(M-H) and pyroelectric current-temperature curves of the single crystal along different crystallographic directions were measured. The results of magnetization measurements which shows the Néel temperature TN of around 90 K and the in-plane magnetic structure of Fe4Nb2O9 are very consistent with the reported magnetic structure obtained by neutron diffraction. The isothermal magnetization curves along [210] direction show spin flop phase transition and a local ferromagnetic loop under 50 K. The critical field HC of spin flop phase transition is found to be 94 kOe. Pyroelectric current-temperature curves show ferroelectric polarization below about 90 K under zero magnetic field, which has not been reported before in single crystal Fe4Nb2O9. At the same time, Fe4Nb2O9 shows magnetoelectric coupling effect. With the increase of magnetic field, the polarization increases to over 300 μC/m2 along a axis under applied magnetic field of 70 kOe.

Magnetocaloric effect in MnCoGe alloys studied by first-principles calculations and Monte-Carlo simulation

The magnetocaloric effect in orthorhombic MnCoGe1−xCux (x = 0.0–0.35) alloys are investigated by combining density functional theory (DFT) and Monte-Carlo simulation. The long-range interactions of the magnetic exchange coupling constants evaluated by the DFT calculations are considered for the Monte-Carlo simulation. The magnetic phase transition temperature is estimated by the divergence of the specific heat, and the isothermal entropy change is computed by integrating the isothermal magnetization curves with the Maxwell relation. The magnetic exchange coupling constants of the Mn-Mn pairs is decreased significantly with increasing of the concentration of Cu from 0.0 to 0.35, resulting in the rapid decrease of the Curie temperature from 618 K to 28 K. Not only the Curie temperature of the MnCoGe alloy is controllable by changing the concentration of Cu at Ge site, but also the magnetocaloric properties such as isothermal magnetic entropy change and relative cooling power are strongly dependent on the concentration of Cu.