Effective Magnetic Moment Μeff Research Articles

Antiferromagnetism, spin-glass state, H–T phase diagram, and inverse magnetocaloric effect in Co2RuO4

Static and dynamic magnetic properties of normal spinel Co2RuO4 = (Co2+) are reported based on our investigations of the temperature (T), magnetic field (H) and frequency (f) dependence of the ac-magnetic susceptibilities and dc-magnetization (M) covering the temperature range T = 2 K–400 K and H up to 90 kOe. These investigations show that Co2RuO4 exhibits an antiferromagnetic (AFM) transition at TN ∼ 15.2 K, along with a spin-glass state at slightly lower temperature (TSG) near 14.2 K. It is argued that TN is mainly governed by the ordering of the spins of Co2+ ions occupying the A-site, whereas the exchange interaction between the Co2+ ions on the A-site and randomly distributed Ru3+ on the B-site triggers the spin-glass phase, Co3+ ions on the B-site being in the low-spin non-magnetic state. Analysis of measurements of M (H, T) for T < TN are used to construct the H–T phase diagram showing that TSG shifts to lower T varying as H2/3.2 expected for spin-glass state whereas TN is nearly H-independent. For T > TN, analysis of the paramagnetic susceptibility (χ) vs. T data are fit to the modified Curie–Weiss law, χ = χ0 + C/(T + θ), with χ0 = 0.0015 emu mol−1Oe−1 yielding θ = 53 K and C = 2.16 emu-K mol−1Oe−1, the later yielding an effective magnetic moment μeff = 4.16 μB comparable to the expected value of μeff = 4.24 μB per Co2RuO4. Using TN, θ and high temperature series for χ, dominant exchange constant J1/kB ∼ 6 K between the Co2+ on the A-sites is estimated. Analysis of the ac magnetic susceptibilities near TSG yields the dynamical critical exponent zν = 5.2 and microscopic spin relaxation time τ0 ∼ 1.16 × 10−10 sec characteristic of cluster spin-glasses and the observed time-dependence of M(t) is supportive of the spin-glass state. Large M–H loop asymmetry at low temperatures with giant exchange bias effect (HEB ∼ 1.8 kOe) and coercivity (HC ∼ 7 kOe) for a field cooled sample further support the mixed magnetic phase nature of this interesting spinel. The negative magnetocaloric effect observed below TN is interpreted to be due to the AFM and SG ordering. It is argued that the observed change from positive MCE (magnetocaloric effect) for T > TN to inverse MCE for T < TN observed in Co2RuO4 (and reported previously in other systems also) is related to the change in sign of (∂M/∂T) vs. T data.

Successive magnetic transitions and magnetocaloric effects in intermetallic compounds RE7Rh3 (RE = Nd, Ho)

In this work, the structure, cryogenic magnetic transition behaviors and magnetocaloric properties in the intermetallic compounds RE7Rh3 (RE = Nd, Ho) have been investigated. Powder X-ray diffraction confirmed the formation of RE7Rh3 (RE = Nd, Ho) with hexagonal Th7Fe3-type crystal structure (space group P63mc). For the Nd7Rh3 compound, it exhibits two successive magnetic phase transitions with increasing temperature, that is, a first-order ferromagnetic-antiferromagnetic transition at Tt = 11.3 K and a second-order antiferromagnetic-paramagnetic transition at TN = 33 K. The reciprocal magnetic susceptibility of the Nd7Rh3 compound obeys the Curie-Weiss law in the paramagnetic region. According to Curie constant, the values of the effective magnetic moment (μeff) and the corresponding paramagnetic Curie temperature (θP) are determined to be 3.39 μB/Nd3+ and 38.6 K, respectively. While for Ho7Rh3, it undergoes paramagnetic to antiferromagnetic transition at TN = 33.5 K followed by the other two magnetic transitions states at Tt = 23.5 K and TSR = 7.2 K with decreasing temperature. The effective magnetic moment of Ho7Rh3 is evaluated to be 10.2 μB/Ho3+, and the negative value of paramagnetic Curie temperature (−10 K) indicates the dominant antiferromagnetic interaction in the Ho7Rh3 compound. For a magnetic field change of 5 T, the maximum magnetic entropy changes of Nd7Rh3 and Ho7Rh3 are calculated to be 6.40 J/kg K and 3.06 J/kg K with the corresponding refrigerant capacity values of 164 J/kg and 85 J/kg, respectively.

Cluster glass transition in the ternary Dy2AgIn3 system determined by neutron diffraction and Ac–Dc magnetization measurements

The crystallographic and magnetic properties of the polycrystalline intermetallic compound Dy2AgIn3 are presented. The compound crystallizes in the hexagonal CaIn2- type structure (space groupP63/mmc). The magnetic susceptibility data reveals a Curie–Weiss (CW) law behavior above120K, with a calculated effective magnetic moment μeff=10.63±0.29μB/Dy3+and a Curie paramagnetic temperatureθp=17.5K±0.5K, demonstrating the dominance of ferromagnetic (FM) couplings in the sample. In the temperature range of 60-120Kit exhibits a Griffith’s phase like behavior. The dc field cooled (FC) and zero field cooled (ZFC) susceptibility, show field dependent irreversible phenomena belowTr~43K, and the ZFC plots present a cusp glass like maxima at31K. The irreversibility temperatureTradopts aH2/3, field dependence of de Almeida–Thouless type line which defines the stability limits in the H-T plane withTr(0)=44.5±0.5K. The ac susceptibility data shows a relative shift in freezing temperature δTf~0.048±0.004, while near the freezing temperature it exhibits a Power- Vogel-Fulcher law dependency characterized by the dynamic exponentszν=7.4, single flip time τ0=10-6sandTg=24.5±0.65K. These values suggest the formation of cluster spin-glass states (CSG). At low angles the neutron diffraction (ND) profiles display diffuse scattering of antiferromagnetic (AFM) origin which is triggered by the ~5nm- magnetic spin clusters.

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.

The magnetic properties of the LaCr3(BO3)4 crystal

This article investigates the magnetic susceptibility, χ(T), of the two-phase (R32 + C2/c) crystal LaCr3(BO3)4 in the temperature range 2–300 K for two orientations of an external magnetic field. It has been established that both structural modifications of lanthanum chromium borate are ordered antiferromagnetically, with each of them having its own Néel temperature (6.5 and 8.5 K). It has been shown that at T &amp;gt; 60 K, the magnetic susceptibility is well described by the Curie–Weiss law with an effective magnetic moment of μeff = 3.86 μB/Cr3+ and a Curie–Weiss temperature of θ = –23 K. Within the Heisenberg spin chain model, taking into account the interchain exchange interaction, the authors have obtained the following exchange-interaction constants: an antiferromagnetic intrachain exchange (J/k = 4.8 K) and a ferromagnetic interchain exchange (J'/k = –0.28 K).

Cyclodextrin-Based Organic Radical Contrast Agents for in vivo Imaging of Gliomas.

Cyclodextrins (CDs), a class of cyclic oligosaccharides formed by α-(1,4) linked glucopyranose units, were functionalized with (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) radicals to prepare water soluble supramolecular organic radical contrast agents (ORCAs) for the in vivo detection of glioma tumor in animal models. A first set of molecules (CDn1, n=6,7,8 is the number of both TEMPO and glucopyranose units) was studied by superconducting quantum interference devices (SQUID) magnetometry in order to define the role of the CD macrocycle on the effective magnetic moment (μeff ). The μeff value increased from 3.982 μB (CD61) to 4.522 μB (CD81) but was limited by intramolecular antiferromagnetic (AF) interactions. A set of water-soluble ORCAs (CDn8, n=6,7,8) was prepared by a sequence of thiol-ene and Cu(I)-catalyzed alkyne-azide "click" reactions. Their 1 H water relaxivities r1 of these ORCAs were between 0.739 mM-1 s-1 (CD68) to 1.047 mM-1 s-1 (CD88) in D2 O/H2 O 9 : 1 (v : v) at 300 K. One of them (CD78) was tested on glioma-bearing rats with reduced side effects and good relaxivity in vivo.

Nickel(II) derivatives based on o-iminobenzoquinone-type ligands: Structural modifications, magnetism and electrochemical peculiarities

New bis-o-iminobenzosemiquinonato derivatives of nickel (imSQC(O)Ph)2Ni (1) and (imSQPh)2Ni (2) that are ligated by functionalized o-aminophenols H2LC(O)Ph and H2LPh, respectively, were synthesized. Complex 1 is distinguished by a square-planar geometry of N2O2 coordination core while the bis-o-iminobenzosemiquinonate 2 demonstrates a slight deviation from planarity. Both complexes 1 and 2 show the strong antiferromagnetic interactions between radical anion ligands as established by variable-temperature magnetic susceptibility measurements. Electrochemical behavior of 1 and 2 is represented by ligand-centered redox transitions: two quasi-reversible one-electron reduction processes and two-electron oxidation one. The salient peculiarity of cyclic voltammogram for 1 is an increase in number of redox waves owing to the quasi-reversible reduction of benzophenone fragments in ligands. Six-coordinated NiII derivative [(imQC(O)Ph)2Ni(H2O)2](OSO2CF3)2 (3) with two o-iminobenzoquinones as well as four-coordinated NiII species [(imSQC(O)Ph)Ni(APC(O)Ph)]CoCp2∙2.1toluene (4∙2.1toluene) including radical-anion and o-amidophenolate forms of redox-active ligand were prepared as products of oxidation and reduction of the initial 1, respectively, in accordance with the CV data. The value of effective magnetic moment (μeff) unambiguously indicates the high-spin state for nodal NiII ion in 3. Low-temperature EPR signal demonstrates rather the ligand-centered nature of unpaired electron in 4 that corresponds to the total doublet ground spin state (S = 1/2) for compound and diamagnetic low-spin (SNi = 0) configuration of the metal center.

Anomalous magnetism in Al doped La2CoMnO6 ceramics

La2CoMn1-xAlxO6 (0 ≤ × ≤ 1.00) samples were synthesized by sol–gel method, and their crystal structure and magnetic properties were investigated. X-ray diffraction reveals a structural transition from monoclinic (space group P21/n) to rhombohedral phase (space group R-3c) with Al content increasing. As envisionedandexpected, the remanent magnetization Mr and ferromagnetic (FM) transition temperature TC dramatically decrease with the increment of Al doping, which is due to the destruction of the long-range Co2+-O-Mn4+ FM super-exchange interaction induced by Al ion doping. However, abnormally increase of coercive field HC and effective magnetic moment μeff appear for × = 0.25. The results of infrared spectrum, Raman spectrum, and X-ray photoelectron spectroscopy illustrate that this anomaly can be attributed to the spin-state transition of Co3+ ions from intermediate spin (IS) to high spin (HS) state with × increasing to 0.25, rather than the valence changes of the magnetic ions. This spin-state transition is probably due to the increase of crystal symmetry with high disorder and the suppression of Jahn-Teller distortion. The suppressing Jahn-Teller distortion favors the stability of the HS state of Co3+ ions.

Shape-controlled microwave hydrothermal synthesis of antiferromagnetic GdVO4 nanowires for magnetocaloric materials

GdVO4 nanowires have been fabricated by a microwave-assisted hydrothermal method with the addition of EDTA (ethylenediaminetetraacetic acid) during synthesis. The GdVO4 nanowires have a lower antiferromagnetic (AFM) ordering temperature (TN) and effective magnetic moment μeff than them of bulk GdVO4. In a field-cooled mode, upward magnetization was found below TN in the magnetization-temperature measurements because of surface effects, where uncompensated surface spins were not ordered as AFM states. With a magnetic field change of 5 T, the maximum value of magnetic entropy change (−ΔSMmax) is 35.77 J kg−1 K−1 at 2.3 K and the relative cooling power is 211.04 J kg−1 with no hysteresis loss. The nanocrystalline GdVO4 nanowires produce a significant reversible magnetocaloric effect (MCE) and can be applied to hydrogen liquefaction as a cryogenic MCE material.

A biradical oxo-molybdenum complex containing semiquinone ando-aminophenol benzoxazole-based ligands

We report a new mononuclear molybdenum(iv) complex, MoOLBISLSQ, in which LSQ (2,4-di-tert-butyl o-semibenzoquinone ligand) has been prepared from the reaction of the o-iminosemibenzoquinone form of a tridentate non-innocent benzoxazole ligand, LBIS, and MoO2(acac)2. The complex was characterized by X-ray crystallography, elemental analysis, IR and UV-vis spectroscopy and magnetic susceptibility measurements. The crystal structure of MoOLBISLSQ revealed a distorted octahedral geometry around the metal centre, surrounded by one O and two N atoms of LBIS and two O atoms of LSQ. The effective magnetic moment (μeff) of MoOLBISLSQ decreased from 2.36 to 0.2 μB in the temperature range of 290 to 2 K, indicating a singlet ground state caused by antiferromagnetic coupling between the metal and ligand centred unpaired electrons. Also, the latter led to the EPR silence of the complex. Cyclic voltammetry (CV) studies indicate both ligand and metal-centered redox processes. MoOLBISLSQ was applied as a catalyst for the oxidative cleavage of cyclohexene to adipic acid and selective oxidation of sulfides to sulfones with aqueous hydrogen peroxide.

Long-range and short-range ordering in 2D honeycomb-lattice magnet Na2Ni2TeO6

The magnetic structure of quasi-two-dimensional (2D) honeycomb lattice Na2Ni2TeO6 has been determined by low-temperature neutron diffraction and the crystal structure fine details at room temperature have been established by a combination of synchrotron and neutron powder diffraction. The atomic structure is described by the P63/mcm space group, but the strong presence of stacking faults defects in layered ordering is found for the first time. Both magnetization and specific heat data indicates an establishment of a long-range antiferromagnetic order with TN = 25 ± 1 K, preceded by a short-range order on 2D honeycomb lattice at about 34 K. Determined effective magnetic moment μeff = 4.35 μB is in excellent agreement with numerical estimation using effective g-factor g = 2.19 directly measured by electron spin resonance. The ground magnetic state at T = 1.5 K is represented by the commensurate zigzag-type magnetic order. Magnetic moments of Ni are almost perpendicular to the honeycomb layers, which antiferromagnetically coupled along the c-direction. Besides, the coherent magnetic scattering area has a disk shape that is homogeneous over the ab plane and compressed along the c-axis that indicates 2D nature of magnetic correlations in the compound. The magnetic diffuse neutron scattering related to the presence of strong short-range spin-spin correlations above TN was observed. Based on our experimental measurements we propose magnetic phase diagram for Na2Ni2TeO6.

Electrical resistivity, magnetic properties and thermoelectric power factor of the polycrystalline compound CeCu4In: Effect of La dilution

In this study we mainly report on the magnetic and thermoelectric power properties of the Ce1-xLaxCu4In compounds. XRD results confirm the orthorhombic-CeCu4: 38In1: 62 type structure for all compositions, as well as Vegard’s rule. Resistivity ρ(T) results show an evolution from coherent Kondo scattering to incoherent single-ion Kondo scattering, with increased La content x. The magnetic susceptibility, χ(T) data indicate paramagnetic behaviour and follow the Curie–Weiss law with effective magnetic moment μeff values across the series close to the value of 2.54μB expected for the free Ce3+-ion. No evidence of metamagnetic transition was observed from the magnetization results, M(μ0H). For selected representatives of the studied series, thermoelectric power S(T) exhibits a positive maximum, which reaches up to 64.5 µV.K−1 for the parent CeCu4In. This maximum of S(T) decreases from 64.5 µV.K−1 to 44.1 µV.K−1 upon 40% La concentration. Similarly, the thermoelectric power factor PF(T) reached a maximum of 32.6 µW.cm.K−1 for the parent CeCu4In and decreases with increase in La content x.

Fabrication and characterization of novel p-Phenylamine-N(4-chloro salicylaldenemine) ligand and its metal complexes and evaluation their anti-corrosion and chemical resistance properties in epoxy/SiO2 nanocomposite for steel surface coating

Schiff base metal complex/epoxy nanocomposite coating engineering is considered a vital corrosion protection model for steel surface applications. To support this concept, several metal (Cr(III), Co(II), Ni(II), Cu(II) and Zr(IV)) complexes of Schiff base ligand named p-Phenylamine-N(4-chloro salicylaldenemine) (HL) were synthesized. The HL was chelated with metal ions as a bidentate manner through NO donor atoms with 1:2 (metal:HL) molar ratio and it was detected by microanalytical procedure. The resulting metal chelates of HL were fully characterized using the conductivity and magnetic moment measurements, UV–Vis, FT-IR, 1H NMR, XRD and TG-DTG analysis. Transmission electron microscope (TEM) and X-ray diffraction (XRD) techniques were accomplished for the silica nanoparticles characterization. Different surface-modified epoxy/SiO2 nanocomposite coating formulations with HL and its metal complexes were prepared without any compatibility problems. The anti-corrosion behavior of the epoxy nanocomposite coated films versus unmodified conventional epoxy was clarified by salt spray accelerated corrosion test. The obtained results demonstrated a considerable improvement in the rust grade, size and frequency of blistering, and adhesion strength of surface modified Ni(II) and Cr(III) complexes nanocomposite coated steel films at the same loading level. To confirm the previous concept, SEM morphology survey and FT-IR chemical structure characterizations for the employed cured coated films after the direct exposure to salt spray aggressive fog were investigated. Chemical immersion strategy was performed to check the acids and alkali resistances of nanocomposite coated films against conventional epoxy. The perfect protective behavior of the Ni(II) and Cr(III) complexes may be attributed to their highly effective magnetic moment (μeff) which leads to enhancing the cross-linking density through the coating layer, thereby enhancing the adhesion between the steel substrate and epoxy matrix.

Synthesis, crystal structures, magnetic properties and antimicrobial screening of octahedral nickel(II) complexes with substituted quinolin-8-olates and pyridine ligands

New nickel(II) compounds, viz. trans-[Ni(LHAQ)2(Py)2]·C6H6 (1), cis-[Ni(LHAQ)2(3-MePy)2] (2), cis-[Ni(L2−MeAQ)2(3-MePy)2] (3), trans-[Ni(L4−MeAQ)2(Py)2]·C6H6 (4), trans-[Ni(L4−OMeAQ)2(Py)2]·C6H6 (5), trans-[Ni(L4−OEtAQ)2(Py)2]·C6H6 (6), trans-[Ni(L4−BrAQ)2(Py)2]·C6H6 (7) and trans-[Ni(L4−ClAQ)2(3-MePy)2]·2(3-MePy) (8) (primary ligands: LXAQ = substituted 5-[(E)-2-(aryl)-1-diazenyl]quinolin-8-olate; secondary ligands: Py = pyridine or 3-MePy = 3-methylpyridine) have been synthesized and characterized by elemental analysis, IR, UV–vis spectroscopy. The magnetic susceptibilities of the compounds were also measured. Single-crystal X-ray diffraction analysis of the compounds revealed octahedral geometries with trans configurations for 1, 4–8 and cis configurations for 2 and 3. The occurrence of intramolecular Ni⋅⋅⋅Hpyridine interactions in 2 and in 3, may account for additional stabilization of their assemblies at least in the solid state. The effective magnetic moment (μeff) in the range 3.02–3.40 BM agree with the expected values for octahedral Ni(II) cations with two unpaired electrons. Ni(II) compounds were also screened for their antimicrobial activity.

Synthesis, structural and DFT interpretation of a Schiff base assisted Mn(III) derivative

A mononuclear MnIII derivative, [Mn(L)(SCN)(H2O)] (1) [where H2L = N,N′-bis(salicyaldehydene)-1,3-diaminopropan-2-ol] has been synthesized and systematically characterized. In 1, the central MnIII ion is linked to the NNOO donor atoms of the potentially binucleating precursor L2− and additionally coordinates one water molecule and the pseudohalide SCN−, thus yielding a distorted octahedral geometry. The UV–Vis spectra of 1 shows an intense band corresponding to a 5T2g − 5Eg transition at 545 nm; thus presuming the octahedral geometry around the Mn ion. The solid and solution EPR spectra of 1 have been simulated with an HP 53150A microwave frequency counter which has confirmed the +3 oxidation state of the metal ion. We have also conducted a DFT computational study which has confirmed that compound 1 self assembles into a two-dimensional network via O‒H⋯O, π–π, and unconventional C‒H … π(SCN) interactions involving the π-system of the thiocyanate. The room temperature magnetic susceptibility of compound 1 has yielded an effective magnetic moment (μeff) value of 4.96 B.M.

Spin transition characteristics of molecular solvates of CuII complexes with nitroxides: sensitivity to the packing type

A method for the synthesis of solvates of dinuclear heterospin complexes of bis(hexafluoroacetylacetonato)copper(ii) with 2-(4-methylpyridin-3-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (LMe) and 2-(4-ethylpyridin-3-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (LEt) of the composition [Cu(hfac)2LR]2 · Solv (Solv = benzene, bromobenzene, toluene, o-xylene, p-xylene) was developed. It was found that a decrease in temperature induces structural transformations of the solid phases of the complexes followed by significant changes in the distances between the paramagnetic centers in the intramolecular exchange clusters {Cu2+-O·-} from 2.321 to 1.974 A. As a result, the temperature dependences of the effective magnetic moment μeff(T) exhibit magnetic features similar to spin transitions. An analysis of the shape of the μeff(T) curves suggested that the magnetic properties of the compounds under study depend primarily on the molecular packing. A comparison of the magneto-structural correlations typical of the [Cu(hfac)2LR]2 · Solv complexes studied in this work with the data obtained earlier for analogous solvates of heterospin polymer chain complexes showed that the spin transition characteristics of the [Cu(hfac)2LR]2 · Solv systems are much less sensitive to the change of the solvent than the corresponding characteristics of the heterospin polymers containing solvate molecules in the interchain space. The magnetic characteristics of the heterospin dimer molecules depend primarily on which cavity between the dimers is filled with solvate molecules. For solvates with monoclinic symmetry, changes in the solvent molecules occupying same-type cavities have almost no effect on the spin transition characteristics in the heterospin exchange cluster.

Magnetic properties and large magnetocaloric effect in Ho3Pd2 compound

Abstract Magnetic transitional behaviors and magnetocaloric effect of the intermetallic compound Ho3Pd2 have been studied. It exhibits a second order magnetic transition from ferromagnetic (FM) to paramagnetic (PM) states at a Curie temperature (TC) of 9.6 K. In the PM region, the magnetic susceptibility of the Ho3Pd2 compound follows the Curie-Weiss law. The paramagnetic Curie temperature (θp) was evaluated to be 5.3 K, and the effective magnetic moment (μeff) to be 10.5 μB/Ho. The positive value of θp indicates the ferromagnetic interactions in the ordering state of Ho3Pd2 and the effective magnetic moment is close to the theoretical value 10.6 μB for the Ho3+ ion, which suggests that the Pd ions in Ho3Pd2 are non-magnetic. Under the magnetic field change of 0–5 T, the maximum magnetic entropy change (−ΔSM) and the refrigerant capacity (RC) for this compound are evaluated to be 18.3 J kg−1 K−1 and 301.5 J kg−1, respectively, with no thermal and field hysteresis loss.

Magnetic and Electrochemical Properties of Lantern-Type Dinuclear Ru(II,III) Complexes with Axial Chloride Ions or Water Molecules

By using [Ru2(O2CC3H7)4Cl]n (1) as a starting material, nBu4N[Ru2(O2CC3H7)4Cl2] (nBu4N+ = tetra(n-butyl)ammonium cation) (2) and [Ru2(O2CC3H7)4(H2O)2]BF4 (3) were prepared. The lantern-type dinuclear structures with axial chloride ions or water molecules were confirmed for 2 and 3 by X-ray crystal structure analyses. The crystal structures of 2 and 3 were compared with that of 1. In the crystal of 2, there were three crystallographically different dinuclear units; the Ru–Ru distances of each unit were 2.3094(3), 2.3046(4), and 2.3034(4) Å, respectively, which were longer than those of 1 (2.281(4) Å) and 3 (2.2584 (7) Å). Temperature dependent magnetic susceptibility measurements were performed for 1 and 2 as well as 3. The effective magnetic moments (µeff) at 300 K were 3.97 (for 1), 4.00 (for 2), and 3.97 µB (for 3), respectively. The decreases in the µeff value were confirmed for all of the complexes due to the large zero-field splitting (D): D = 68 cm−1 for 1, 78 cm−1 for 2, and 60 cm−1 for 3. Cyclic voltammograms measured in CH2Cl2 with a electrolyte of nBu4N(BF4) showed the Ru25+/Ru24+ process at −0.2–−0.4 V (vs. SCE) and the Ru26+/Ru25+ one at 1.3–1.4 V (vs. SCE), of which potentials were confirmed by the DFT calculation for nBu4N[Ru2(O2CC3H7)4Cl2].

An Unusual Valence State: Trivalent Europium in Intermetallic Eu2 Ir3 Al9.

Eu2 Ir3 Al9 , synthesized from the elements in tantalum tubes, is one of the rare examples for trivalent europium in the field of intermetallic compounds. The compound crystallizes in the Y2 Co3 Ga9 -type structure (space group Cmcm), with lattice parameters fitting in between the isostructural samarium and gadolinium compounds. In the crystal structure, the Eu atoms form Al3 -triangle-centered honeycomb layers and exhibit a coordination number of 17 in the shape of a fivefold-capped hexagonal prism (Eu@Ir6 Al6 +Al5 ). Magnetic measurements indicate an overall low susceptibility, in line with van Vleck paramagnetism caused by the Eu3+ cations. Fits of the susceptibility yield a coupling constant of λ=290(10) K and an effective magnetic moment of μeff =4.56(1) μB , in line with a slight hybridization of the 7 F0 and 7 F1 state. 151 Eu Mössbauer spectroscopic investigations unambiguously prove the presence of solely Eu3+ in the bulk material.

Fascinating Physical Properties of 2D Hybrid Perovskite [(NH3)(CH2)7(NH3)]CuClxBr4−x, x = 0, 2 and 4

The 2-D organic–inorganic hybrid perovskites of the formula [(NH3)(CH2)7(NH3)]CuClxBr4−x, x = 0, 2 and 4 were prepared by slow evaporation from ethanolic solution in stoichiometric ratio 1:1 (organic/inorganic). Microchemical analysis and x-ray diffraction (XRD) were used to confirm the formation of the presently investigated hybrids. Differential scanning calorimetry (DSC) indicated order–disorder transitions at T1 = 357 K, T2 = 388 K, and T3 = 398 K for x = 0, 2 and 4 of the three heptain diammonium Cu hybrid perovskites, respectively. These transitions are in good agreement with the electrical permittivity results at different frequencies and temperatures. Optical properties and estimated band gap energy reveal that the band gap energy decreases sharply with replacement of Cl ion by Br ion where the band gap energy of [(NH3)(CH2)7(NH3)]CuBr4, x = 0 (denoted 2C7CuBr) is 1.6 eV (brown color) and for [(NH3)(CH2)7(NH3)]CuCl4, x = 4 (denoted 2C7CuCl) is 2.6 eV (yellow color). The differential magnetic susceptibility of 2C7CuBr in the temperature range 80–300 K indicates the effective magnetic moment μeff = 2.05 BM.