Temperature Dependence Of Magnetic Susceptibility Research Articles

Large positive magnetoresistance and Dzyaloshinskii\u2013Moriya interaction in CrSi driven by Cr 3d localization

Spin chiral systems with Dzyaloshinskii–Moriya (DM) interaction due to broken inversion symmetry are extensively studied for their technological applications in spintronics and thermoelectrics. Here, we report an experimental study on the magnetization, magnetoresistance (MR) and electronic structure of a non-centrosymmetric compound CrSi with B20 crystal structure. Both magnetization and MR shows competing ferromagnetic (FM) and antiferromagnetic (AFM) correlations with the FM correlations being comparatively weaker indicating the presence of DM interaction in CrSi. A large positive MRsim ,25% obtained at 5 K and 5 T magnetic field arises due to the stronger AFM correlations. Resonant photoemission shows both localized and itinerant nature of Cr 3d electrons to be present in CrSi and this is supported by the temperature dependence of magnetic susceptibility. Drastic variation in the density of states along with valence band broadening at low temperature indicates the increase in hybridization between Cr 3d and Si 3s–3p states which enhances the localization effects. Spin polarized itinerant Cr 3d electrons give rise to AFM spin density wave in CrSi. Magnetic interaction between the localized and itinerant Cr 3d electrons are found to be crucial for realizing DM interaction in this system. Spectral density of states derived from high resolution valence band measurements provides evidence of electronic topological transition in CrSi. Large density of polarized itinerant electrons which varies with temperature and the large positive MR with AFM correlations suggests CrSi as a potential candidate for both the thermoelectric and spintronics applications.

Two-dimensional magnetism in α−CuV2O6

Several previous studies reported that a one-dimensional Heisenberg chain model is inadequate in describing the magnetic properties of the low-dimensional quantum antiferromagnet $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{CuV}}_{2}{\mathrm{O}}_{6}$, but the origin for this observation has remained unclear. We have reinvestigated the magnetic properties of $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{CuV}}_{2}{\mathrm{O}}_{6}$ and found that our anisotropic magnetic susceptibility, neutron-powder diffraction, and electron paramagnetic spin-resonance measurements are in good agreement with extensive density-functional theory ($\mathrm{DFT}+U$) total energy calculations which indicate that the correct spin lattice model for $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{CuV}}_{2}{\mathrm{O}}_{6}$ is rather a $S=1/2$ 2D-Heisenberg antiferromagnetic lattice. The magnetic susceptibility data are well described by a rectangular Heisenberg antiferromagnet with anisotropy ratio $\ensuremath{\alpha}\ensuremath{\sim}$ 0.7 consistent with the DFT results. Quantum Monte Carlo simulations of the magnetic susceptibilities for a rectangular lattice Heisenberg antiferromagnet were performed in the anisotropy range 0.5 $\ensuremath{\le}\ensuremath{\alpha}\ensuremath{\le}$ 1.0. The results of the Quantum Monte Carlo calculations were cast into a Pad\'e approximant which was used to fit the temperature-dependent magnetic susceptibility data. Neutron-powder-diffraction measurements were used to conclusively solve the collinear antiferromagnetic structure of $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{CuV}}_{2}{\mathrm{O}}_{6}$ below the N\'eel temperature of $\ensuremath{\sim}22.4$ K.

Temperature and time-dependent luminescence of single crystals of KTb3F10

This work deals with the spectroscopic properties of single crystalline samples of KTb3F10. Green luminescing KTb3F10 is an efficient UV radiation converter with a quantum yield of about 40% upon UV-A excitation, while it is also an efficient scintillator upon excitation by 20–50 kV X-ray photons. The temperature dependence of the integral photoluminescence as well as the decay time of KTb3F10 monitored for the Tb3+ emission show that the internal quantum yield between 100 and 800 K is almost constant, while the external quantum yield is modulated, likely due to a change in reabsorption at elevated temperatures. In contrast, the low temperature range between 3 and 63 K reveals a change of the local Tb3+ environment in KTb3F10, which is indicated by an anomaly in the heat capacity and by a strong change of the decay time as well as by a distinct shift of the photoluminescence spectra at low temperatures. In addition, temperature dependent magnetic susceptibility measurements and a structure refinement based on single crystal X-ray diffraction data were performed.

Solid solutions EuAu4Cd2−x Mg x with a remarkably stable ferromagnetic ground state

Abstract Samples of the solid solutions EuAu4Cd2−x Mg x were synthesized from the elements in sealed tantalum ampoules. The elements were reacted at a maximum temperature of 1273 K followed by slow cooling. For crystal growth, the polycrystalline samples were ground to powders, pressed to pellets and annealed again. All samples crystallize with the tetragonal YbAl4Mo2-type structure, space group I4/mmm. The solid solution extends up to x = 1 and the Cd/Mg substitution has only a minor influence on the lattice parameters. The samples have been characterized by powder X-ray diffraction and the structure of EuAu4Cd1.58(2)Mg0.42(2) was refined from single crystal X-ray diffractometer data: a = 715.46(14), c = 549.96(11) pm, wR2 = 0.0334, 180 F 2 values and 11 variables. The striking crystal chemical motifs of the EuAu4Cd2−x Mg x structures are Eu@Au12 and (Cd/Mg)@Au8(Cd/Mg)2 polyhedra and linear Cd/Mg chains in form of a tetragonal rod packing with distances of 275 pm for Cd/Mg–Cd/Mg. Temperature dependent magnetic susceptibility measurements of all samples from the solid solutions EuAu4Cd2−x Mg x revealed Curie–Weiss behavior and stable divalent europium. All samples are ordered ferromagnetically around T = 16 K, and magnetization isotherms at 3 K classify these materials as soft ferromagnets. It is remarkable that the structural Cd/Mg disorder within the chains does not influence the ferromagnetic ground state. The divalent nature of europium in these intermetallics was exemplarily studied for the EuAu4Cd1.4Mg0.6 sample by 151Eu Mössbauer spectroscopy. At 6 K the isomer shift is −9.95(4) mm s−1 and one observes full magnetic hyperfine field splitting with B hf = 27.1(1) T.

Ternary plumbides ATPb2 (A = Ca, Sr, Ba, Eu; T = Rh, Pd, Pt) with distorted, lonsdaleite-related substructures of tetrahedrally connected lead atoms

Abstract The plumbides CaTPb2 (T = Rh, Pd), EuTPb2 (T = Rh, Pd, Pt), SrTPb2 (T = Rh, Pd, Pt) and BaTPb2 (T = Pd, Pt) were obtained by direct reactions of the elements in sealed tantalum tubes in an induction furnace. The moisture sensitive polycrystalline samples were characterized by X-ray powder diffraction. They crystallize with the orthorhombic MgCuAl2-type structure, space group Cmcm. The structures of CaRhPb2 (a = 433.78(3), b = 1102.06(8), c = 798.43(6) pm, wR = 0.0285, 432 F2 values and 16 variables) and EuPdPb2 (a = 457.24(5), b = 1158.27(13), c = 775.73(8), wR = 0.0464, 464 F2 values and 16 variables) were refined from single crystal X-ray diffractometer data. The characteristic structural motif is the distorted tetrahedral substructure built up by the lead atoms with Pb–Pb distances of 326–327 pm in CaRhPb2 and of 315–345 pm in EuPdPb2. With increasing size of the alkaline earth (Eu) cation, the lead substructure becomes more anisotropic with a shift of the [TPb2] polyanions from three- to two-dimensional, leading to significantly increased moisture sensitivity. Temperature dependent magnetic susceptibility studies reveal Pauli paramagnetism for SrRhPb2, SrPtPb2, BaPdPb2 and BaPtPb2. EuRhPb2 and EuPdPb2 are Curie–Weiss paramagnets with stable divalent europium as is also evident from 151Eu Mössbauer spectra. EuRhPb2 is a ferromagnet with T C = 17.7(2) K, while EuPdPb2 orders antiferromagnetically at T N = 15.9 K. This is in agreement with the full magnetic hyperfine field splitting of the 151Eu Mössbauer spectra at T = 6 K.

Deformational and magnetic effects in Cu–Al–Mn alloys

A comparative analysis of the magnetic, size and deformation effects of martensitic transformation in aged Cu–Al–Mn alloys with a minimum width of the temperature hysteresis was performed. According to the experimental studies of the behavior of alloys during martensitic transformations, the changes in temperature dependences of thermal expansion, magnetic susceptibility and electrical resistance, depending on preliminary thermomagnetic treatment of alloys, were found. The thermomagnetic treatment contributes to a change in the magnitude of volume effect of martensitic transformation. Using magnetic analysis, the state and distribution of precipitated particles, affecting both the magnetic characteristics and the volume effects of martensitic transformation in the alloys, were determined.

Polymorphism and Molten Nitrate Salt-Assisted Single Crystal to Single Crystal Ion Exchange in the Cesium Ferrogermanate Zeotype: CsFeGeO4.

Two polymorphs of a new cesium ferrogermanate zeotype, CsFeGeO4, were synthesized using the molten CsCl-CsF flux growth approach at 900 °C. The orthorhombic polymorph, referred to as (1), crystallizes in the centrosymmetric nonpolar Pbcm space group. The compound exhibits a three-dimensional porous framework structure composed of disordered (Fe/Ge)O4 corner-sharing tetrahedra that generate large eight-sided channels running down the b-axis. These channels are occupied by Cs ions that provide charge balance to the anionic framework. Minor modifications in the reaction conditions lead to the synthesis of a monoclinic polymorph of CsFeGeO4, referred to as (2), crystallizing in the noncentrosymmetric polar space group P21 and exhibiting an identical framework structure to (1), albeit featuring ordered FeO4 and GeO4 tetrahedra. Solid state synthesis of CsFeGeO4 produces a polycrystalline mixture of (1) and (2), referred to as (6). Polarization-electric field (P-E) measurements of (6) indicate that the material is not ferroelectric. Powder second harmonic generation (SHG) measurements of (2) and (6) revealed them to be SHG active with intensities of 1.5 and 0.2 times that of α-SiO2, respectively. The temperature dependent magnetic susceptibility of (2) exhibits a downturn at T = 2.6 K, indicative of antiferromagnetic ordering. First-principles calculations in the form of density functional theory showed that (1) and (2) differ in stability by only 1.3 meV/atom, with (2) being the thermodynamically stabilized phase. Additional calculations for (1), using molten nitrate as reference, predicted the formation of energetically favorable phases, KFeGeO4 (3) and RbFeGeO4 (4). They were subsequently prepared via a molten nitrate salt bath treatment of (1) to replace Cs with K and Rb, affording (3) and (4) as single-crystal to single-crystal ion exchange products. Structure determination and property measurements for a pyroxene phase, CsFeGe2O6, referred to as (5), are also reported. This compound crystallized as a side product in the flux synthesis of CsFeGeO4.

Dynamical mean-field study of Vanadium diselenide monolayer ferromagnetism

To understand the magnetism of VSe2, whose monolayer form has recently been reported to be a room temperature ferromagnet, here, the combined method of conventional density functional theory with dynamical mean-field theory has been adopted. This higher-level computation method enables us to resolve many of existing controversies and contradictions in between theory and experiment. First of all, this new approach is shown to give the correct magnetic properties of both bulk and two-dimensional limit of VSe2 which demonstrates its superiority to the conventional methods. The results demonstrate that monolayer VSe2 without charge density waves is a ferromagnet with ordering temperature of 250 K. From the direct simulation of temperature-dependent magnetic susceptibility and ordered moment, it is shown that its ferromagnetism is clearly two-dimensional in nature. Further, it is shown that this ferromagnetic order is vulnerable to extra charge dopings which provides the important insight to elucidate recent experimental controversies.

Corrigendum: Entrapment of a Pseudo-Tetrahedral CoII Center by Thioether Sulfur Bound {Co2 (μ-L)} Fragments: Synthesis, Field-Induced Single-Ion Magnetism and Catechol Oxidase Mimicking Activity.

It has come to the attention of the authors that Figure 6, the values of effective magnetic moments for complexes 1 and 2, giso, E/D values in Abstract section and in the Magnetic properties sections, giso and E/D values in Table 1, and D value for complex 2 in Conclusions section were changed mistakenly in the final stage of manuscript preparation. The data published in Figure 6 reveal the results obtained for older measurement on different batches of the complexes. The correct values, corresponding to the results obtained for the same batches of complexes for which the DC and AC magnetic measurements were done, are presented below. These mistakes do not affect the integrity of the research and overall conclusions of the published paper. The corrected Figure 6 and corresponding text are given below. Magnetic properties. Investigation of the magnetic features of complexes 1 and 2 proceeded using a PPMS device on which the temperature (1.9–300 K) and field (0–9 T) dependent magnetic data were obtained (Figure 6). Figure 6 Temperature dependence of the effective magnetic moment (inset: temperature dependence of the molar magnetic susceptibility) for complexes 1 and 2 (Left). The isothermal magnetizations measured in the range of B=0–9 T and at T=2, 5 and 10 K (Right). The magnetic properties of the complexes are primarily due to the presence of central tetrahedral CoII ion since octahedral LS-CoIII ions are diamagnetic. The value of effective magnetic moment (μeff) of complex 1 at 300 K is 3.5 μB, slightly lower than the spin-only value of 3.9 μB for S=3/2, g=2.0. Thereafter upon cooling the μeff value raises slightly up to ca 75 K and then, it drops sharply to a minimum at 1.9 K, where it adopts the value of 3.2 μB. In the case of complex 2, the μeff value at 300 K is 5.0 μB which is again much higher that the calculated value for isotropic S=3/2 spin. It decreases gradually upon cooling up to ca 50 K and then, it declines sharply to a minimum at 4.4 K reaching the value of 4.2 μB. The high μeff value at 300 K indicates considerable contribution of a spin-orbit coupling to the ground state in the complex 2. Isothermal magnetization experiments (Figure 6) for 1 and 2 in the applied field range of B=0–9 T at different constant temperatures T=2, 5 and 10 K reveal that the magnetization does not show saturation suggesting the presence of magnetic anisotropy. To extract the parameters affected by magnetic anisotropy arising from crystal field effects (g, D), both the susceptibility and magnetization data were fitted simultaneously. The best fit parameters were calculated using the PHI program package[26] for S=3/2 and they are as follows: giso=2.05, D=−23.6 cm−1, E/D=0, zJ/hc=0 cm−1, χTIP=−13.0×10−4 cm3 mol−1 for 1 and giso=2.61, D=−24.3 cm−1, E/D=0.01, zJ/hc=0.05 cm−1, χTIP=2.0×10−4 cm3 mol−1 for 2. The presence of temperature-independent paramagnetism (TIP) term accounts for the four surrounding CoIII ions. The observed D values for 1 and 2 are relatively close compared to those (−31.31 cm−1 and −21.88 cm−1) obtained in our previous investigations with complexes having similar molecular structures.[10] The authors wish to emphasize that with these corrections, the reported ZFS parameters relevant for the discussion of single molecule magnetism (i.e. the D values) did not change at all and the overall conclusions published in the original version of the article are not affected.

Crystal structure and magnetic properties of a pentanuclear copper(II) 12-metallacrown-4 complex derived from glutaroimide-dioxime

Reaction of copper(II) perchlorate with glutaroimide-dioxime (H3gido) in MeOH solution led to a quasi co-planar 12-metallacrown-4 complex [Cu5(Hgido)4(ClO4)2]·CH3OH(1). The structure of complex 1 has been confirmed by X-ray analysis: two types of similar 12-metallacrown-4 units are connected into 1D chain by perchlorate anions. The temperature dependent magnetic susceptibilities analysis indicates that the antiferromagnetic exchange interaction through the Cu(II)peripheral–Cu(II)central and Cu(II)peripheral–Cu(II)peripheral pathways are J1 = -41.3 and J2 = -14.2 cm−1, respectively. The field-dependent magnetization at 2 K confirms the ground state of St = 3/2.

Eu1\u2009\u2212\u2009xSrxAu4Cd2: a ferromagnetic solid solution with adjustable Curie temperature

Samples of the solid solution Eu1–xSrxAu4Cd2 (YbAl4Mo2 type, space group I4/mmm) with x = 0.2, 0.4, 0.6, and 0.8 were synthesized from the elements by annealing in sealed tantalum ampoules. The structures of Eu0.66Sr0.34Au4.12Cd1.88 and Eu0.22Sr0.78Au4.10Cd1.90 were refined from X-ray single crystal diffractometer data. Besides the expected Eu/Sr mixing on the 2a sites the diffraction data revealed also a small degree of Cd/Au mixing on the 4d sites of the cadmium chains. Temperature dependent magnetic susceptibility data show divalent europium and ferromagnetic ground states for all samples and a linear decrease of the Curie temperature from 16.3 K for EuAu4Cd2 to 2.9 K for Eu0.2Sr0.8Au4Cd2. Magnetization isotherms characterize the Eu1 − xSrxAu4Cd2 samples as soft ferromagnets. The divalent nature of europium is underpinned by 151Eu Mössbauer spectra. The decreasing Curie temperature goes along with a decreasing magnetic hyperfine field at 6 K.Graphic abstract

Magnetically induced electric polarization in Ba3Fe2O5Cl2 with tunable direction in three dimensions

The correlation between magnetism and electric polarization in a chiral insulating magnet $\mathrm{B}{\mathrm{a}}_{3}\mathrm{F}{\mathrm{e}}_{2}{\mathrm{O}}_{5}\mathrm{C}{\mathrm{l}}_{2}$ has been investigated. The temperature dependence of magnetic susceptibility shows an anomaly at 564 K, suggesting the onset of antiferromagnetic order of $\mathrm{F}{\mathrm{e}}^{3+}$ moments. Electric polarization appears in a magnetic field below ${T}_{\mathrm{N}}$ due to the spin-direction-dependent metal-ligand hybridization. The direction of the electric polarization can be controlled in three-dimensional space by changing the direction of an external magnetic field. This compound also shows an antiferromagnetic-to-weak-ferromagnetic transition accompanied by a structural phase transition at 140 K.

Synthesis, characterization and magnetic studies for a series of compounds having a trinuclear bimetallic Cu2(II)/Ln(III) system

New trinuclear complexes having the general formula [LnCu2(Cl)2(L)2(H2O)2]Cl·H2O, where L (H2L) = Schiff base ligand and Ln = La (1), Nd (2), Sm (3), Gd (4), Tb (5) and Er (6), have been synthesized from the hexadentate ligand (2,2′-{propane-1,3-diylbis[nitrilo(E)methylylidene]}bis(6-methoxyphenol)). The synthesized compounds were characterized by FT-IR and UV–visible spectroscopy, and thermogravimetric analysis. The X-ray structure for 3 completely describes the coordination behavior around each metal censer, along with the geometric shape. The magnetization of the synthesized trinuclear bimetallic complexes were measured initially by vibrating sample magnetometry, with special reference to temperature dependent magnetic susceptibility measurements for Cu2IILaIII (1), Cu2IINdIII (2), Cu2IISmIII (3), Cu2IIGdIII (4), Cu2IITbIII (5) and Cu2IIErIII (6) to assess their intrinsic magnetic behavior. The interactions between the copper and lanthanide ions present in the complexes were determined to evaluate their magnetic strength. It is inferred from the magnetic susceptibility data that the synthesized compounds are paramagnetic in nature, whereas the J- values describe the presence of antiferromagnetic and ferromagnetic interactions between the metal(s) ions for 1–3 and 4–6 respectively.

Hydrogen influence in the UNiAl-UNiGa system: Structure and magnetism

Hydrogen absorption studies on UNiAl1-xGax were performed as part of our investigation of UTX compounds. The whole series crystallizes in the hexagonal structure of the ZrNiAl type (s.g. P-62m). The amount of hydrogen absorbed has a decreasing tendency with increasing Ga concentration. Studies of the temperature dependence of magnetic susceptibility indicate certain increase of the critical temperature of magnetic ordering in the hydrides but the increment becomes smaller with increasing Ga concentration as a result of smaller H absorption and concomitant changes in the crystal structure.

Strongly Correlated Molecular Magnet with Curie Temperature above 60 K

Summary Two-dimensional crystals with ferromagnetic ordering would lead to unprecedented possibilities for magnetic, magneto-optic, and magnetoelectric applications. However, long-range ferromagnetic ordering in two-dimensional van der Waals materials is strongly diminished by thermal fluctuation, while three-dimensional systems show the stiffness of magnetic ordering temperature to magnetic fields. Here, we report the discovery of intrinsic ferromagnetic ordering temperature of 60 K in an iron/tetracyanoquinodimethane layer via superconducting precursor. In such a molecular ferromagnet, an unprecedented control of ferromagnetic fluctuation temperature by ∼200% improvement is realized through magnetic fields. We demonstrate magnetodielectric coupling with a concomitant transition in magnetic ordering. A small magnetic field of 0.01 T enables an effective route to realize a sizable transition shift in magnetodielectric states. Stimulated by photoirradiation, it manifests a hidden metallic conducting state, declaring a metallic ferromagnet. The molecular ferromagnet and photoirradiation-induced hidden metallic phase present a “holy grail” in the field of molecular conducting magnets.

Cooling rates of pyroclastic deposits inferred from mineral magnetic investigations: a case study from the Pleistocene M\xfdtina Maar (Czech Republic)

Tephra layers of the Mýtina Maar, Czech Republic, contain ferrimagnetic Mg–Al-rich titanomagnetite, which is suggested to originate from a fractionated alkaline CO2-rich lithospheric mantle melt. We investigated the magnetic mineralogy and Curie temperature (TC) from tephra deposits of two drill cores (< 9 m depth). TC calculated (208 ± 14 °C) from chemical composition (Fe2+0.8Mg0.5Fe3+1.1Al0.3Ti0.3O4) is in accordance with TC retrieved from cooling curves of temperature-dependent magnetic susceptibility measurements (195–232 °C). However, thermomagnetic curves are irreversible either with lower (type I) or higher (type II) TC in the heating curve. All curves show transition temperatures above ca. 390 °C, indicating maghemitization. We interpret the irreversibility of TC (∆TC) in terms of different degrees of cation ordering, overprinted or masked by different degrees of maghemitization, which is a low-temperature phenomenon. Negative ∆TC indicates that original deposited titanomagnetite has cooled faster and, therefore, has stored a lower degree of cation ordering compared to heating/cooling rate of 11 °C/min in the Kappabridge. Type II with positive ∆TC indicates higher degree of cation ordering, and, therefore, slower cooling rate. The central part of this deposit shows most severe maghemitization, indicating rather wet emplacement. We, therefore, suggest different eruption styles for deposition of type I pyroclastics with more phreatomagmatic and type II pyroclastics with more phreato-Strombolian eruption styles. Our study is a new approach to discriminate different cooling histories in maar deposits using the Curie temperature of titanomagnetite. We suggest that this method has the potential to discriminate different emplacement modes resulting from different eruption styles.

Synthesis, Crystal Structure, and Cooperative 3d–5d Magnetism in Rock Salt Type Li4NiOsO6 and Li3Ni2OsO6

Two new transition metal oxides with the nominal chemical compositions of Li4NiOsO6 and Li3Ni2OsO6 were successfully synthesized. Both compounds crystallize in an ordered rock salt structure type in the monoclinic C2/m space group. The crystal structures were determined using both synchrotron X-ray and time-of-flight neutron, powder diffraction data. In both phases, Ni2+ ions are present while oxidation states of osmium are +6 and +5 in Li4NiOsO6 and Li3Ni2OsO6, respectively. Ni2+ ions in the hypothetical fully ordered phase form a honeycomb arrangement in the ab crystallographic plane and these hexagons are centered by osmium ions. The magnetic layers are separated along the c axis by the octahedra, which are centered by Li+ (or Li+/Ni2+, depending on the chemical compositions). Crystal structure refinements reveal that there is some degree of mixed occupancy in cationic positions. Temperature dependent magnetic susceptibility data for both phases show ferrimagnetic transitions with predominant antiferromagnetic (AFM) interactions among 3d electrons of nickel and 5d electrons of osmium. Iso-thermal magnetization loops as a function of the applied magnetic field below the transition temperatures confirm the ferrimagnetic nature in magnetic transitions. Temperature dependent heat capacity data, however, did not exhibit any anomaly in either phase, indicating the absence of long-range magnetic ordering. The lack of long-range order for both Os5+ and Os6+-based compounds was also confirmed by low temperature neutron diffraction data down to 10 K. Temperature dependent AC magnetic susceptibility data in various frequencies for both samples indicate that Li4NiOsO6 exhibits spin-glass-like behavior, while the transition temperature for Li3Ni2OsO6 is nearly frequency independent.

A new gadolinium complex with 1, 3-bis (carboxymethyl) imidazolium chloride ionic liquid: Solvothermal synthesis, structure and magnetic properties

A new 3D complex namely [Gd4(C7H7N2O4)6(H2O)12]·Cl6·9H2O (1) was solvothermally synthesized by using 1,3-bis (carboxymethyl) imidazolium cation as a ligand. Single crystal X-ray analysis reveals that 3D positive charged framework was formed by Gd–O coordination bonds,and Gd3+ ions have two kinds of coordination environments. The free counter Cl− ions and lattice H2O locate in cavities of 1 through extensive H-bonds and electrostatic attractions between the Cl−/H2O and the positive framework. The thermogravimetric analysis (TGA) shows the organic framework decomposed at temperature above 345 °C, giving the final products Gd2O3. The temperature dependent magnetic susceptibility displays antiferromagnetic interaction at temperature below 15.2 K, once above 15.2 K, compound 1 converts into paramagnetic interaction.

Magnetic properties of ErFe2Al10 and ErRu2Al10 single crystals

We investigated the field dependences of magnetization M(H), the temperature dependences of magnetic susceptibility χ(T), and specific heat C(T) of orthorhombic ErFe2Al10 and ErRu2Al10 single crystals in a temperature range of 0.46–300 K. For ErFe2Al10, an antiferromagnetic phase transition was observed at the Néel temperature TN 1.7 K, and M(H) of the b-axis at 0.47 K indicated a metamagnetic transition at 0.07 T. The easy axis in M(H) and χ(T) curves is the b-axis and the hard axis is the c-axis. A large anisotropy was seen in M(H) and χ(T) curves in the three crystal axes. In the case of ErRu2Al10, magnetic successive phase transitions were observed at 1.3 and 1.0 K. Spin-flops were observed in M(H) curves at 0.25 T on the a- and b-axes in 0.46 K. The easy axis in M(H) curves is the a-axis and the hard axis is the c-axis. We proposed a magnetic structure from the result of χ(T) curves, whereby the magnetic moment of Er was perpendicular to the c-axis and closely aligned to the [110] direction below TN. The C(T) curve showed sharp peaks at corresponding temperatures. For both compounds, hump structures were observed in the temperature dependences of magnetic specific heat above TN. These structures were Schottky anomalies that came from excited doublets.

Frequency Dependent Charge Transport and Spin State Switching Characteristics of Fe(phen)₂(NCS)₂ in Polymer.

We report on the bistability in spin states of spin crossover (SCO) compound Fe(phen)₂(NCS)₂ in polymer (polypyrrole) by frequency (1-100 kHz) and temperature dependent (305-457 K) electrical conductivity measurements. The structure and growth of SCO compounds in conducting polymer are obtained by scanning electron microscopy, X-ray diffraction and optical absorption measurements. The thermal dependence of ac conductivity σ(ω) shows the clear formation of a hysteresis loop in its cooling and heating cycle due to the difference in conductivity in high spin and low spin state. The size, shape and width of the hysteresis loops are found to be critically dependent on the applied frequency and/or the ratio between SCO and polymer. The ac conductivity is found to exhibit a dispersive behavior following Jonscher's law: σ(ω) ∝ ωn below a critical frequency ωc, above which it is found to monotonically decrease with increasing frequency. The thermal dependence of the exponent n and ωc is also explored. The charge transport phenomena are explained in the framework of hopping of charge carriers. The data reveals that addition of polymer can play an important role to tune the conductivity of SCO compounds and its spin state dependence characteristics which may be quite helpful for fabricating future spin-based devices. Temperature dependent magnetic susceptibility measurement also confirms the spin transition behavior of the SCO/ppy composite samples. These SCO/ppy composite samples can be taken as the reliable nanomaterials fabricated with the concept of future spin based nanoarchitectonics.