Dc Magnetization Measurements Research Articles

Fabrication of cold sintered soft magnetic composites using oxalate coated iron powders.

The advancement of electric vehicles to replace gas-powered cars requires more efficient designs for electric motors. Three-dimensional flux motors, employing high-strength soft magnetic composites made from powdered metals, are considered a promising alternative to current state-of-the-art motors. In this study, we demonstrate that utilizing cold sintering of iron particles coated with hydrated oxalate leads to the creation of a soft magnetic composite with approximately 55 MPa of transverse rupture strength when compacted at 100ºC. Upon subsequent heat treatment up to 700ºC, the strength significantly rose to almost 219 MPa. During the heat treatment process, the oxalate undergoes transformation into iron/copper oxides. We systematically examined this chemical transformation using diffuse reflectance infrared Fourier transform spectroscopy, scanning electron microscopy, transmission electron microscopy, and electron dispersive x-ray spectroscopy. Our findings from AC and DC magnetic measurements of the cold-sintered toroid, in relation to heat treatment temperature, demonstrate an increase in DC permeability with rising heat treatment temperatures. Additionally, our analysis of AC core loss data revealed that hysteresis power losses dominate the performance at lower heat treatment temperatures (< 300°C), beyond which dynamic core losses show significant escalation.

Intertwined crystal structure, magnetic, and charge transport properties in mixed valent A-site ordered manganite NdBaMn2O6

In the present work, we report a correlation between crystal structure, magnetic, and electrical properties in an exotic magnetic compound, NdBaMn2O6 having ∼92% ordering between Nd and Ba, investigated using temperature-dependent synchrotron x-ray diffraction (XRD), dc magnetization and transport measurements. Temperature-dependent XRD data reveals that the compound undergoes various complex crystallographic phase transitions from high-temperature (T > 320 K) P4/mmm phase to intermediate (320 K – 280 K) Cmmm phase to a mixed (Cmmm and P21am) phase (280 K – 220 K) and to low-temperature P21am phase (T < 220 K). It is found that these crystallographic phase compositions play a crucial role in controlling its magnetic and transport properties. Temperature-dependent dc magnetization data show a sharp drop at the onset of mixed phase (Cmmm + P21am) at 280 K followed by a broad hump at ∼ 220 K where mixed phase to P21am transition occurs, thus indicating a correlation between the structural and magnetic properties. The dc magnetization in the mixed phase region is calculated by considering a superposition of the magnetic moments of Cmmm and P21am phases weighted by the fraction of each phase, which exactly follows the experimental magnetization data. Temperature variation of resistivity data shows a jump at ∼260 K, a temperature corresponding to 50–50% phase composition of Cmmm and P21am phases. The compound shows insulating behavior over a whole temperature range as confirmed from the resistivity data. Further, application of magnetic field causes a shift of magnetic and transport transition temperatures which may be due to the magnetic field induced structural transition in the system.

Magnetic and magnetocaloric properties of rare earth intermetallic compound Gd3Co4Ge13

Magnetic and magnetocaloric properties of polycrystalline Gd3Co4Ge13 (Cubic, Yb3Rh4Sn13-type, Space group Pm-3n, No. 223, cP40) have been studied by carrying out dc magnetization measurements in applied magnetic fields up to 140 kOe. The compound Gd3Co4Ge13 orders antiferromagnetically at 9 K (TN). The antiferromagnetism appears to be weak and with increasing applied magnetic fields, ferromagnetic interactions become dominant. This field-induced antiferromagnetic to ferromagnetic state that is marked as a change from inverse to normal magnetocaloric effect in the isothermal magnetic entropy change vs temperature plot around TN. At 2 K, the magnetization shows a tendency toward saturation in applied magnetic field and a magnetic moment of 5.3 µB per Gd3+ is obtained in 140 kOe field.

Novel lanthanide complexes with quinoline-2-carboxylic acid: Structural variety and magnetism

By means of the reaction of lanthanide chlorides with quinaldic (quinoline-2-carboxylic, HQA) acid in an aqueous-ethanolic medium in the presence of pyridine, the following complexes were obtained: the known binuclear [Nd2(QA)6(H2O)6]·3H2O (1) one and the novel compounds built of binuclear dicationic and mononuclear anionic moieties [Ln2(QA)4(H2O)4]2+[Ln(QA)4(H2O)]ˉ2·2EtOH·6H2O (Ln = Gd (2), Dy (3), Er (4), Yb (5)), as well as the anionic mononuclear one, [Hpy2]+[Er(QA)4]ˉ·4H2O (6). The complexes 2–5 were characterized by dc and ac magnetic measurements. Complex 3 exhibits the properties of a single-molecule magnet (SMM) in a zero static field with remagnetization barrier (Δeff/kB) of 82 K, while the other complexes display the properties of field-induced SMMs with the Δeff/kB values of 24, 19, and 33 K for the complexes 2, 4, and 5, respectively.

Magnetic and magnetocaloric properties of the multi-component Mn0.5Fe0.5Ni0.95Cr0.05Si0.95Al0.05 intermetallic compound

The first-order phase transition and associated magnetocaloric properties of Mn0.5Fe0.5Ni0.95Cr0.05Si0.95Al0.05 have been studied by x-ray diffraction and dc magnetization measurements. The diffraction data for the sample showed that both the orthorhombic and hexagonal crystalline phases coexisted at room temperature. The temperature dependence of magnetization was measured at a constant field of 0.2 T. The first-order phase transition was observed at 325 K during heating and at 306 K during cooling, showing a thermomagnetic hysteresis of 19 K. For magnetic field change of 5 T, the entropy changes evaluated from the isothermal magnetization data peaked at 322 K during warming and at 313 K during cooling, showing a thermomagnetic hysteresis of 9 K. This difference in the magnitude of the thermomagnetic hysteresis was attributed to the virgin effect due to stress and crack formation during the first cooling from hexagonal to orthorhombic phase. Peak entropy changes of −16 J kg−1 K−1 and −42 J kg−1 K−1 were observed on heating for field changes of 2 and 5 T, respectively. The related refrigeration capacities were 74 J/kg (2 T) and 194 J/kg (5 T).

Intensity and lifetime ratiometric luminescent thermometer based on a Tb(III) coordination polymer.

A three-dimensional terbium(III) coordination polymer of formula [Tb(bttb)0.5(2,5-pzdc)0.5]n (1) [H4bttb = 1,2,4,5-tetrakis(4'-carboxyphenyl)benzene and H2-2,5-pzdc = 2,5-pyrazinedicarboxylic acid] was obtained under hydrothermal conditions. The bttb4- tetraanion in 1 adopts the bridging and chelating-bridging pseudo-oxo coordination modes while the 2,5-pzdc2- dianion exhibits a rather unusual bis-bidentate bridging pseudo-oxo coordination mode, both ligands being responsible for the stiffness of the resulting 3D structure. Solid-state photoluminescent measurements illustrate that 1 exhibits remarkable green luminescence emission, the most intense band occurring in the region of 550 nm (5D4 → 7F5) with lifetimes at the millisecond scale. Thermometric performances of 1 reveal a maximum relative sensitivity (Sm) of 0.76% K-1 at 295 K (δT = 0.05 K), constituting a TbIII ratiometric solid luminescent thermometer over the physiological temperature range. Variable-temperature static (dc) magnetic susceptibility measurements for 1 in the temperature range 2.0-300 K show the expected behavior for the depopulation of the splitted mJ levels of the 7F7 ground state of the magnetically anisotropic terbium(III) ion plus a weak antiferromagnetic interaction through the carboxylate bridges. No significant out-of-phase magnetic susceptibility signals were observed for 1 in the temperature range 2.0-10.0 K, either in the absence or presence of a static dc magnetic field.

Control of the geometry and anisotropy driven by the combination of steric and anion coordination effects in CoII complexes with N6-tripodal ligands: the impact of the size of the ligand on the magnetization relaxation time.

Four mononuclear CoII complexes of formula [Co(L)(SCN)2(CH3OH)0.5(H2O)0.5]·1.5H2O·0.75CH3OH (1), [Co(L1)Cl2]·H2O·2CH3CN (2), [Co(L1)(SCN)2]·1.5H2O·CH3OH (3) and [Co(L1)]ClO4·2CH3OH (4) were prepared from the N6-tripodal Schiff base ligands (S)P[N(Me)NC(H)2-Q]3 (L) and (S)P[N(Me)NC(H)1-ISOQ]3 (L1), where Q and ISOQ represent quinolyl and isoquinolyl moieties, respectively. In 1, the L ligand does not coordinate to the CoII ion in a tripodal manner but using a new N,N,S tridentate mode, which is due to the fact that the N6-tripodal coordination promotes a strong steric hindrance between the quinolyl moieties. However, L1 can coordinate to the CoII ions either in a tripodal manner using CoII salts with poorly coordinating anions to give 4 or in a bisbidentate fashion using CoII salt-containing medium to strongly coordinating anions to afford 2 and 3. In the case of L1, there is no steric hindrance between ISOQ moieties after coordination to the CoII ion. The CoII ion exhibits a distorted octahedral geometry for compounds 1-3, with the anions in cis positions for the former and in trans positions for the two latter compounds. Compound 4 shows an intermediate geometry between an octahedral and trigonal prism but closer to the latter one. DC magnetic properties, HFEPR and FIRMS measurements and ab initio calculations demonstrate that distorted octahedral complexes 1-3 exhibit easy-plane magnetic anisotropy (D > 0), whereas compound 4 shows large easy-axis magnetic anisotropy (D < 0). Comparative analysis of the magneto-structural data underlines the important role that is played not only by the coordination geometry but also the electronic effects in determining the anisotropy of the CoII ions. Compounds 2-3 show a field-induced slow relaxation of magnetization. Despite its large easy-axis magnetic anisotropy, compound 4 does not show significant slow relaxation (SMR) above 2 K under zero applied magnetic fields, but its magnetic dilution with ZnII triggers SMR at zero field. Finally, it is worth remarking that compounds 2-4 show smaller relaxation times than the analogous complexes with the tripodal ligand bearing in its arms pyridine instead of isoquinoline moieties, which is most likely due to the increase of the molecular size in the former one.

Magneto-structural correlation in lanthanide luminescent [2.2]paracyclophane-based single-molecule magnets.

The association of lanthanide ions and paracyclophane derivatives has been very scarcely reported in the literature. In this study, elaboration of five coordination lanthanide complexes involving the 1,4(1,4)-dibenzenacyclohexaphane-12,43-diylbis(diphenylphosphine oxide) ligand (L) was achieved with the determination of single-crystal X-ray diffraction structures of four mononuclear complexes of formula [Ln(hfac)3(L)] (hfac- = 1,1,1,5,5,5-hexafluoroacetylacetonate) (Ln = Dy(III) (1-Dy) and Yb(III) (2-Yb)) and [Ln(tta)3(L)] (tta- = 2-tenoyl-trifluoroacetylacetonate) (Ln = Dy(III) (3-Dy) and Yb(III) (4-Yb)) and one dinuclear complex [Na(Dy2(hfac)6(L)2)](BArF) (BArF- = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) (5-Dy). The compounds were characterized using elemental analysis, IR spectroscopy, DC and AC magnetic measurements and photophysical investigations. L is an efficient organic chromophore for the sensitization of both visible Dy(III) (1-Dy) and near-infrared Yb(III) (2-Yb and 4-Yb) luminescence. The combination of excitation and emission spectra allowed the determination of the crystal field spitting of both the 2F7/2 ground state and 2F5/2 excited state for 2-Yb and 4-Yb. Moreover, 3-Dy and the two Yb(III) derivatives displayed field-induced single-molecule magnet (SMM) behaviour with slow magnetic relaxation occurring through the Raman process only for 2-Yb and 4-Yb, whereas a combination of Orbach and Raman processes was identified for 3-Dy.

New cyanido-bridged iron(II) spin crossover coordination polymers with an unusual ladder-like topology: an alternative to Hofmann clathrates.

Two new cyanido-bridged {FeIIMII} double chains were obtained by reacting cyanido anions [M(CN)4]2- with complex cations [FeII(tptz)]2+ (preformed in situ by mixing a hydrated tetrafluoroborate salt of iron(II) and a tptz ligand, tptz = 2,4,6-tri(2-pyridyl)-1,3,5-triazine) having the general formula [FeII(tptz)MII(CN)4]·2H2O·CH3CN, where M = Pd (1) or Pt (2). Additionally, two molecular complexes formulated as [FeII(tptz)2][MII(CN)4]·4.25H2O, where M = Pd (3) or Pt (4), were subsequently obtained from the same reaction, as secondary products. Single crystal X-ray analysis revealed that 1 and 2 are isostructural and crystallize in the P-1 triclinic space group. Their structure consists of a double-chain with a ladder-like topology, in which cyanido-based [M(CN)4]2- metalloligands coordinate, through three CN- ligands and three [FeII(tptz)]2+ complex cations. Compounds 3 and 4 are also isostructural and crystallize in the P1̄ triclinic space group, and the X-ray structural data show the formation of [FeII(tptz)2]2+ and [MII(CN)4]2- ionic units interconnected through H-bonds and π⋯π stacking supramolecular interactions. The static DC magnetic measurements recorded in the temperature range of 2-300 K showed that 1 and 2 exhibit incomplete spin transition on cooling, which is also confirmed by single crystal XRD analysis and Mössbauer spectroscopy. Compounds 3 and 4 are diamagnetic, most likely due to the encapsulation of Fe(II) in a tight pocket formed by two tptz ligands that preserve the low-spin state in the temperature range of 2-400 K.

Exploring superconductivity in Ba3Ir4Ge16: Experimental and theoretical insights

We explore both experimental and theoretical aspects of the superconducting properties in the layered caged compound, Ba3Ir4Ge16. Our approach integrates muon spin rotation and relaxation (μSR) measurements with magnetization and heat capacity experiments, accompanied by first-principle calculations. The compound’s bulk superconductivity is unequivocally established through DC magnetization measurements, revealing a critical temperature (TC) of 5.7 K. A noteworthy characteristic observed in the low-temperature superfluid density is its saturating behavior, aligning with the features typical of conventional Bardeen-Cooper-Schrieffer (BCS) superconductors. The assessment of moderate electron-phonon coupling superconductivity is conducted through transverse field μSR measurements, yielding a superconducting gap to TC ratio (2Δ(0)∕kBTC) of 4.04, a value corroborated by heat capacity measurements. Crucially, zero field μSR measurements dismiss the possibility of any spontaneous magnetic field emergence below TC, highlighting the preservation of time-reversal symmetry. Our experimental results are reinforced by first-principles density functional calculations, underscoring the intricate interplay between crystal structure and superconducting order parameter symmetry in caged compounds. This comprehensive investigation enhances our understanding of the relationship between crystal structure and superconductivity in such unique compounds.

Spin-phonon coupling driven magnetodielectric effect in low-dimensional complex magnetic BaGdFeO4 system

In this report, we have investigated the detailed magnetodielectric properties associated with spin-phonon coupling in the BaGdFeO4 polycrystalline compound, X-ray diffraction study confirms the orthorhombic crystal structure with a space group of Pnma. The DC magnetization measurements indicate the complex magnetic behavior with multiple magnetic transitions at TN1 = 62 K and TN2 = 31 K. In the field-dependent magnetization study, field-induced metamagnetic transitions and their temperature dependence have been attributed to the competing magnetic interactions of two magnetic sub-lattices with rare-earth (Gd3+) and Fe3+ magnetic spins. Dielectric measurements have revealed the correlation of observed dielectric anomalies with the magnetic transitions. The frequency-independent and magnetic field-dependent dielectric anomalies, along with the corresponding magnetic transitions, thus corroborate the subtle magnetodielectric coupling studied by temperature-dependent magnetodielectric measurements. We discuss possible origins for the magnetodielectric behavior in terms of weak spin-phonon interactions, as confirmed by the temperature-dependent Raman spectra measurements.

Crystal structure and physical properties of the new AcNi6Si6 compounds (Ac: Th, U)

The crystal structure of the new ternary ThNi6Si6 and UNi6Si6 intermetallic compounds has been investigated by means of both single crystal and powder X-ray diffraction followed by Rietveld refinement. Both compounds adopt the tetragonal CeNi6Si6-type structure, crystallizing in the space group P4/nbm (No. 125) (Pearson’s symbol tP52). This prototype is a ternary defect-derivative of the binary NaZn13-type. A group-theoretical analysis carried out in this work illustrates the structural relationship occurring among the aristotype NaZn13-type, the partially disordered CeNi6Si6 and the fully ordered YNi6Si6 hettotype crystal structures.Zero-field low-temperature electrical resistivity data show a metallic behaviour for both materials. DC magnetic measurements from room temperature down to 2 K reveal diamagnetic behaviour for ThNi6Si6, indicating that Ni atoms do not carry any magnetic moment. On the other hand, the effective magnetic moment per formula unit for UNi6Ni6 is found to be µeff = 3.07(1) µB, suggesting a trivalent (U3+) or tetravalent (U4+) state for U atoms with partial delocalization of 5 f electrons. No magnetic ordering down to 2 K is seen in UNi6Si6. No superconducting transition was detected, neither in UNi6Si6 nor in ThNi6Si6 in the available temperature interval (2 K ≤ T ≤ 300 K).

Probing Evolution of the Flux-Pinning Landscape in REBCO Coated Conductors Caused by Gamma Irradiation Using DC and AC Magnetometry: A Novel Approach to Tokamak Magnet Material Development

Optimisation of REBCO coated conductor tapes specifically for use in nuclear fusion will help improve the magnet component lifetimes in future tokamak reactor power plants. The focus of this work was exploration of a novel approach to irradiation studies on REBCO tapes, utilising multiple magnetic measurements to probe evolution of the REBCO flux-pinning landscape more deeply than reported in other studies, for the purpose of identifying primary limiting factors affecting performance. Gamma irradiation experiments were conducted, and pre-/post-irradiation results from DC and AC magnetic measurements using a Physical Property Measurement System (PPMS) are discussed. Magnetisation critical current density (Jc) decreased in all samples with increasing dose, except for the silver overlayer-only samples which did not contain artificial pinning centres (APCs), where Jc increased with dose. Removal of the copper stabiliser coupled with the presence of APCs allowed gamma irradiation to induce pinning force maximum peak shifts, from above 14 T before irradiation to below 9 T afterwards. Flux creep rate varied with the evolving pinning landscape, and the degree of Jc degradation directly correlated with creep rate fluctuations post-irradiation. Changes in critical temperature and diamagnetic saturation also corresponded with changes in Jc and flux creep rate. The major conclusion from this study was that minimisation of flux creep rate is the key to maintenance of performance under fusion-relevant operating conditions. Flux creep manifests as problematic AC losses in all high-temperature superconducting machines; therefore, future work will focus on reduction/prevention of the phenomenon to enhance longevity of performance in any application.

Influence of Ge-doping on the collinear and non-collinear antiferromagnetic phases of Mn[formula omitted]Si[formula omitted] alloy

Effect of Ge-doping at the non-magnetic site (Si-site) of the Mn-based binary alloy Mn5Si3 has been explored through temperature-dependent x-ray diffraction, dc-magnetic, and electrical transport measurements. All the doped alloys show D88 type hexagonal structure with space group P63/mcm at room temperature and undergoes two structural distortions, hexagonal (P63/mcm) → orthorhombic (Ccmm) → orthorhombic (Cc2m), on cooling. The magnetic characters of these orthorhombic (Cc2m), orthorhombic (Ccmm), and hexagonal (P63/mcm) phases are non-collinear antiferromagnetic (AFM1), collinear antiferromagnetic (AFM2), and paramagnetic (PM), respectively. Doping of Ge results in a significant increase in the AFM1 to AFM2 transition temperature (TN1). However, the AFM2 to PM transition point remains unchanged. In addition, a reasonable increase in the critical field values of the AFM1 to AFM2 transition via another non-collinear antiferromagnetic phase (AFM1′) with increasing Ge concentration has been observed, indicating the strengthening of AFM1 and AFM1′ phases over the AFM2 phase. Such behaviors make the observation of unusual magnetic properties of undoped Mn5Si3 alloys, like inverted hysteresis loop (IHL) and thermomagnetic irreversibility (TI), more evident for these Ge-doped alloys. Further, this study unfolds the presence of conventional and inverse magnetocaloric effect and they found to decrease with Ge doping. An interesting interplay for positive and negative magnetoresistance has also been observed in all the studied alloys.

Honey-like Odor Meets Single-Ion Magnet: Synthesis, Crystal Structure, and Magnetism of Cobalt(II) Complex with Aromatic Trans-Cinnamic Acid

The hexacoordinate Co(II) complex [Co(neo)2(cin)][BPh4]·½Me2CO (1·½Me2CO) containing trans-cinnamic acid (Hcin) and neocuproine (neo) was prepared. The compound 1·½Me2CO was characterized via single-crystal X-ray analysis, FT-IR spectroscopy, and magnetic measurements. The coordination polyhedron of the complex cation adopts a deformed octahedron shape, and cinnamate exhibits a bidentate mode of coordination, which is unusual for mononuclear Co(II) cinnamate complexes. The analysis of DC magnetic measurements with zero-field splitting (ZFS) spin Hamiltonian revealed large magnetic anisotropy defined by the axial ZFS parameter D = +53.2 cm−1. AC susceptibility measurements revealed the slow relaxation of magnetization under the applied field; thus, 1·½Me2CO behaves as a field-induced single-molecule magnet. The analysis of magnetic properties was also supported by CASSCF/NEVPT2 calculations.

Exploring magnetocaloric and heat capacity behavior in Fe doped Mn5Ge3 alloy

Magnetocaloric properties of hexagonally structured Mn5−xFexGe3 (x=0.15, 0.3, and 0.5) alloys have been investigated using DC magnetization and heat capacity measurements. The maxima of entropy change, −ΔSmmax∼5.04(5.57) J/kg K, along with an adiabatic temperature change of ΔTadmax∼5.05(7.25) K was observed for x=0.15(0.5) at an applied magnetic field H=5 T. With the scaling analysis of −ΔSm, the rescaled curves collapse onto a single universal curve anticipated by the mean-field theory, revealing a second-order type of magnetic transition. Furthermore, −ΔSmmax follows a power law of Hn with n=0.597(3), 0.591(3), and 0.586(3) for Mn5−xFexGe3 (x=0.15, 0.3, and 0.5) alloys, respectively. The refrigerant capacity (RC) is increased from 400 J/kg (for x=0.15) to 420 J/kg (for x=0.5) with Fe doping in Mn5Ge3. Moreover, the coefficient of refrigerant performance (CRP) enhances with Fe doping from 0.06 (for x=0.15) to 0.1 (for x=0.5). Thus, high RC and reasonable CRP values for earth-abundant Mn-based Mn–Fe–Ge alloys promise the potential to replace the high-cost rare-earth (Gd) and heavy metal-based metallic magnetocaloric systems for use in environment-friendly magnetic refrigeration technology.

The Depairing Current Density of a Fe(Se,Te) Crystal Evaluated in Presence of Demagnetizing Factors

The effect of the demagnetizing factor, regarding the determination of the de-pairing current density Jdep, has been studied in the case of a Fe(Se,Te) crystal, using DC magnetic measurements as a function of a magnetic field (H) at different temperatures (T). First, the lower critical field Hc1(T) values were obtained, and the demagnetization effects acting on them were investigated after calculating the demagnetizing factor. The temperature behaviors of both the original Hc1 values and the ones obtained after considering the demagnetization effects (Hc1demag) were analyzed, and the temperature dependence of the London penetration depth λL(T) was obtained in both cases. In particular, the λL(T) curves were fitted with a power law dependence, indicating the presence of low-energy quasiparticle excitations. Furthermore, by plotting λL−2 as a function of T, we found that our sample behaves as a multigap superconductor, which is similar to other Fe-11 family iron-based compounds. After that, the coherence length ξ values were extracted, starting with the Hc2(T) curve. The knowledge of λL and ξ allowed us to determine the Jdep values and to observe how they are influenced by the demagnetizing factor.

Unraveling the magnetic properties and nature of exchange interactions of Mn5−x Fe x Ge3 (0.15 ≤ x ≤ 0.5) alloys

We report the structural and magnetic properties of arc-melted Fe-doped Mn5Ge3 alloys. In this study, Mn5−x Fe x Ge3 (x = 0.15, 0.3, and 0.5) alloys were subjected to DC magnetic measurements in order to examine the nature of magnetic interaction via critical exponents study in the asymptotic critical region. The critical exponents β, γ and δ are obtained independently from different methods. For Mn4.85Fe0.15Ge3, β = 0.338, γ = 1.146 and δ = 4.39; for Mn4.7Fe0.3Ge3, β = 0.337, γ = 1.244 and δ = 4.69 and for Mn4.5Fe0.5Ge3, β = 0.328, γ = 1.195 and δ = 4.64. The values of critical exponents obtained are found to be close to the 3D Ising universality class (β = 0.325, γ = 1.241, and δ = 4.82). Analyses based on the Renormalization group theory predictions reveal that the spin interactions are short-range extended types beyond the nearest neighbors due to the presence of a different set of Mn–Mn interactions with an unequal magnitude of exchange strengths in the Mn5−x Fe x Ge3 alloys.

Enantiomeric Complexes Based on Ruthenium(III) and 2,2'-Biimidazole: X-ray Structure and Magnetic Properties.

We have prepared and characterized two Ru(III) compounds based on the 2,2'-biimidazole (H2biim) ligand, namely, a single complex of formula cis-[RuCl2(H2biim)2]Cl·4H2O (1) and a racemic mixture of formula {cis-[RuCl2(H2biim)2]Cl}2·4H2O (2), which contains 50% of Ru(III) complex 1. Both compounds crystallize in the monoclinic system with space groups C2 and P21 for 1 and 2, respectively. These complexes exhibit the metal ion bonded to four nitrogen atoms from two H2biim molecules and two chloride ions, which balance part of the positive charges in a distorted octahedral geometry. Significant differences are observed in their crystal packing, which leads to the observation of differences in their respective magnetic behaviors. Despite having imidazole rings in both compounds, π-π stacking interactions occur only in the crystal structure of 2, and the shortest intermolecular Ru···Ru separation in 2 is consequently shorter than that in 1. Variable-temperature dc magnetic susceptibility measurements performed on polycrystalline samples of 1 and 2 reveal different magnetic behaviors at low temperatures: while 1 behaves pretty much as a magnetically isolated mononuclear Ru(III) complex with S = 1/2, 2 exhibits the behavior of an antiferromagnetically coupled system with S = 0 and a maximum in the magnetic susceptibility curve at approximately 3.0 K.

Order–disorder phase transition and elastic-to-plastic vortex creep crossover in a triclinic iron pnictide superconductor (Ca_{0.85}La_{0.15})_{10}(Pt_3As_8)(Fe_2As_2)_5

Vortex matter in layered high-T_c superconductors, including iron-pnictides, undergo several thermodynamic phase transitions due to the complex interplay of pinning energy, thermal energy and elastic energy. Moreover, the presence of anisotropy makes their vortex physics even more intriguing. Here, we report a detailed vortex dynamics study, using dc magnetization measurements, in a triclinic iron-pnictide superconductor (Ca_{0.85}La_{0.15})_{10}(Pt_3As_8)(Fe_2As_2)_5, with a superconducting transition temperature, T_csim 31 K. A second magnetization peak (SMP) feature is observed for magnetic field perpendicular (Hparallelc) and parallel (Hparallelab) to the crystal plane. However, its fundamental origin is quite different in both directions. For Hparallelc, the SMP can be well explained using an elastic-to-plastic vortex creep crossover, using collective creep theory. In addition, a possible rhombic-to-square vortex lattice phase transition is also observed for fields in between the onset-field and peak-field related to the SMP. On the other hand, for Hparallelab, a clear signature of an order-disorder vortex phase transition is observed in the isothermal M(H) measurements at Tge 6 K. The disordered phase exhibits the characteristics of entangled pinned vortex-liquid. We construct a comprehensive vortex phase diagram by displaying characteristic temperatures and magnetic fields for both crystal geometries in this unique superconducting compound. Our study sheds light on the intricate vortex dynamics and pinning in an iron-pnictide superconductor with triclinic symmetry.