Low-temperature Magnetic Measurements Research Articles

Effect of magnetic entropy in the thermoelectric properties of Fe-doped Fe2VAl full-Heusler alloy

The effect of spin entropy on the transport of heat/charge carriers in the Fe-doped full-Heusler alloy Fe2+xVAl1-x with x = 0–0.1 has been studied through low-temperature magnetic and thermoelectric measurements. Magnetization (M) measurements confirm itinerant-electron weak-ferromagnetic behavior. A systematic increase of the magnetic transition temperature TC (from 40 K to 223 K) and of the saturation magnetization (from 0.13 to 0.41μB/Fe) with increasing Fe doping (from x = 0 to 0.1) is observed. Applying a magnetic field causes significant suppression of the Seebeck coefficient (S) and the entropy term (S/T) with a negative magnetoresistance near TC for all weak-ferromagnetic samples, demonstrating a clear effect of spin fluctuations. Analyzing M(T) and S(T), we rule out sizeable magnon drag contributions. A large spin fluctuations-induced enhancement in the thermoelectric power factor PF of about 18 % is achieved for x = 0.1 near TC when compared to measurements in a magnetic field of 7 T. The actual improvement in PF is even much higher, as the S shows a significant enhancement (about 34 %) compared to the estimated diffusion term of S(T) at TC. The number of point defects also increases with Fe doping, causing a significant reduction of the lattice thermal conductivity. This study demonstrates the role of spin fluctuations in enhancing the thermopower/thermoelectric performance of Fe-doped Fe2VAl and opens a vista for the strategy's applicability for various thermoelectric materials.

(Invited) Magnetism of Tb3N@C80 Endofullerenes

Tb3N@C80 was one of the first trimetallic endofullerenes to be studied in view of its magnetization where the microscopic picture of 3 Tb magnetic moments non-collinearly aligned by the ligand field of the central nitrogen ion was proposed [1]. The triangular geometry results in a net molecular magnetization of two Tb3+ ions or 18 μB. Today, this is confirmed with 23 possible pseudospin arrangements of the 3 Tb magnetic moments, resulting in a frustrated magnetic ground state with fluctuating pseudospins [2]. This picture does not include coherent tunneling of the magnetization, which is predicted within an 8-dimensional Hamiltonian and can be tested with low temperature magnetization measurements. Experimentally, we find a low temperature hysteresis that identifies Tb3N@C80 as a single molecule magnet. More surprisingly, we observe room temperature ferromagnetism in cubic single crystallites of the molecules using SQUID magnetometry. Since the magnetic interaction between adjacent carbon cages is expected to be dipolar it is neglected in the explanation of magnetic order above 3 K [3] and it is challenging to explain this finding with endofullerene magnetism. We present a series of analytical chamistry results of samples with and without room temperature ferromagnetism.[1] M. Wolf et al. Angew. Chem. Int. Ed. 44, 3306 (2005).[2] R. Westerström et al. Phys. Rev. B, 89, 060406(R) (2014).[3] A. Kostanyan et al. Phys. Rev. B, 101, 134429 (2020).

Inducing a tunable skyrmion-antiskyrmion system through ion beam modification of FeGe films

Skyrmions and antiskyrmions are nanoscale swirling textures of magnetic moments formed by chiral interactions between atomic spins in magnetic noncentrosymmetric materials and multilayer films with broken inversion symmetry. These quasiparticles are of interest for use as information carriers in next-generation, low-energy spintronic applications. To develop skyrmion-based memory and logic, we must understand skyrmion-defect interactions with two main goals—determining how skyrmions navigate intrinsic material defects and determining how to engineer disorder for optimal device operation. Here, we introduce a tunable means of creating a skyrmion-antiskyrmion system by engineering the disorder landscape in FeGe using ion irradiation. Specifically, we irradiate epitaxial B20-phase FeGe films with 2.8 MeV Au4+ ions at varying fluences, inducing amorphous regions within the crystalline matrix. Using low-temperature electrical transport and magnetization measurements, we observe a strong topological Hall effect with a double-peak feature that serves as a signature of skyrmions and antiskyrmions. These results are a step towards the development of information storage devices that use skyrmions and antiskyrmions as storage bits, and our system may serve as a testbed for theoretically predicted phenomena in skyrmion-antiskyrmion crystals.

High-Pressure Induced Continuous Structural Evolution of Kagome Antiferromagnet MgMn3(OH)6Cl2: A Structural Analogue to Quantum Spin Liquid Herbertsmithite.

MgMn3(OH)6Cl2 serves readily as the classical Heisenberg kagome antiferromagnet lattice spin frustration material, due to its similarity to herbertsmithite in composition and crystal structure. In this work, nanosheets of MgMn3(OH)6Cl2 are synthesized through a solid-phase reaction. Low-temperature magnetic measurements revealed two antiferromagnetic transitions, occurring at ∼8 and 55 K, respectively. Utilizing high-pressure synchrotron radiation X-ray diffraction techniques, the topological structural evolution of MgMn3(OH)6Cl2 under pressures up to 24.8 GPa was investigated. The sample undergoes a second-order structural phase transition from the rhombohedral phase to the monoclinic phase at pressures exceeding 7.8 GPa. Accompanying the disappearance of the Fano-like line shape in the high-pressure Raman spectra were the emergence of new Raman active modes and discontinuities in the variations of Raman shifts in the high-frequency region. The phase transition to a structure with lower symmetry was attributed to the pressure-induced enhancement of cooperative Jahn-Teller distortion, which is caused by the mutual substitution of Mn2+ ions from the kagome layer and Mg2+ ions from the triangular interlayer. High-pressure ultraviolet-visible absorption measurements support the structural evolution. This research provides a robust experimental approach and physical insights for further exploration of classical geometrical frustration materials with kagome lattice.

Multiple magnetic transition and magnetocaloric properties in the mixed valence Eu8CuNi2.5Si42.5 type I clathrate compound

We investigated the magnetocaloric and electrical transport properties of the Eu8CuNi2.5Si42.5 clathrate compound, synthesized by an arc melting and annealing method. X-ray photoemission spectroscopy revealed a mixed valence state of Eu2+ and Eu3+. The low-field and low-temperature magnetic measurements indicated a multiple magnetic transition, from ferromagnetic near 35 K to antiferromagnetic at 25 K. Increasing the magnetic field led to the broadening of antiferromagnetic peaks and a final ferromagnetic state under high magnetic fields, indicative of spin reorientation. The transition from a ferromagnetic to an antiferromagnetic state was further corroborated by specific heat measurements. We noted spontaneous magnetization at low temperatures via magnetic hysteresis and Arrott plot analysis. The coexistence of an antiferromagnetic ground state (attributed to the Eu2+ ions) and ferromagnetic clusters (associated with the Ni2+ ions) was supported by spontaneous magnetization at low temperatures in the antiferromagnetic state. The magnetocaloric analyses revealed a high spin entropy change over a broad temperature range for Eu8CuNi2.5Si42.5, which implies its potential as a robust low-temperature magnetocaloric material, distinguished by its high refrigerant capacity.

Thermal evolution of low-temperature magnetic texture modulation in fept thin films by direct visualization

Patterns of ferroic domains and domain walls are being intensively studied to implement new logic schemes. Any technological application of such objects depends on a detailed understanding of them. Using low-temperature magnetic force measurements (10–300 K), the evolution of ferromagnetic stripes on equiatomic FePt thin films is thoroughly analyzed. Since FePt is known to develop a transition from in-plane homogeneous magnetization to stripe domains upon varying its thickness, multiple samples are studied demonstrating the well-established reduction upon thickness decrease and a non-trivial dependence on temperature. Moreover, the room-temperature uniform distribution of the pattern evolves into a distorted one upon temperature cycling. Finally, dissimilar stripe patterns are obtained upon reducing and increasing temperature indicating the states are dependent on the history of applied stimuli rather than the parametric conditions.

Fabrication and properties of nano-CeO<sub>2</sub> doped Y-Ba-Cu-O bulk superconductors

Single-domain Y-Ba-Cu-O (YBCO) bulk superconductors can be widely used in the superconducting maglev, cryomagnets, motors/generators fields. In order to improve the performance of the YBCO bulk superconductors further, in this work, nano-CeO<sub>2</sub> doped YBCO bulk superconductors are fabricated by two infiltration growth techniques (011-IG and 211-IG) respectively, in which two solid pellets of compositions Y<sub>2</sub>O<sub>3</sub>+1.15BaCuO<sub>2</sub>+0.1CuO+1wt.% nano-CeO<sub>2</sub> and Y<sub>2</sub>BaCuO<sub>5</sub> (Y-211)+1 wt.% nano-CeO<sub>2</sub> are employed. And a novel pit-type seeding mode is used to prevent the film seed from moving in the heat treatment process, then the growth morphologies, microstructures and superconducting properties of the samples are investigated. The results show that at a low doping level (1 wt.%), the normal growth of the YBCO crystal is not affected, and fully-grown single-domain YBCO bulk superconductors can be successfully prepared by the two techniques. Furthermore, the positions of the seeds do not move at all, which proves the effectiveness of the new seeding mode. The perpendicular growth sector boundaries on the top surfaces of the samples and clear (00<i>l</i>) series X-ray diffraction (XRD) peaks both prove the high <i>c</i>-axis orientations and high growth quality of the samples. The scanning electron microscopy (SEM) results indicate that the nano-CeO<sub>2</sub> doping can effectively refine the sizes of the Y-211 micro-particles in the bulk superconductors, and this method is applicable to both techniques. Low-temperature magnetization measurement shows that the nano-CeO<sub>2</sub> doped sample prepared by the 011-IG method shows obviously better <i>J</i><sub>c</sub> property than the undoped sample at low fields, indicating that the refined Y-211 particles can effectively enhance the δ<i>l</i>-type pinning. In addition, compared with the 211-IG-processed sample, the 011-IG-processed sample performs better in terms of levitation force, microstructure and <i>J</i><sub>c</sub> property, thus the 011-IG method is a more promising preparation process. The results of this study are important in improving the performance of the YBCO bulk superconductors and optimizing the fabrication technique further.

Pressure-induced structural evolution to a nearly perfect kagome lattice in β-Mn2(OH)3Cl nanosheets

The frustrated magnets exhibiting kagome geometries and the investigation of their structure-property relationships have garnered substantial attention as potential candidates for quantum spin liquid (QSL). In this study, β-Mn2(OH)3Cl nanosheets with distorted kagome geometries were synthesized via a solid-state reaction, and low-temperature magnetic measurements revealed a spin-glass-like magnetic phase transition around 40 K in the frustrated β-Mn2(OH)3Cl. A pressure-induced structural phase transition was further realized by employing in situ synchrotron X-ray diffraction, leading to a hexagonal crystal structure with a nearly perfect kagome lattice of magnetic Mn2+ ions. High-pressure Raman and UV–vis absorption measurements indicates that the topological evolution can be attributed to the synergistic effects of pressure driven internal hydrogen bonds and the intrinsic Jahn-Teller effects. This study provides a strategy for synthesizing candidate compounds of QSL and sheds light on the mechanism underlying the topological evolution of kagome lattices under high pressure.

Porous Silicon and Silicon Nanotubes with Embedded FePt Nanoparticles Investigated by High Temperature Magnetic Measurements

Porous silicon (PSi) and silicon nanotubes (SiNTs) are presented as a platform for filling with FePt nanostructures. The difference of the magnetic characteristics between the two systems is figured out. Furthermore, the FePt filled templates are compared with the same template materials filled with Ni/Co by electrodeposition.The porous silicon is produced by anodization of a highly doped n-type silicon wafer in a 10 wt% HF solution. The produced morphology offers separated pores of about 50 nm and a mean distance between the pores of 50 nm. The SiNTs are fabricated in using an array of ZO wires as template, subsequent silicon deposition and finally etching off the ZO. The inner diameter of the tubes and also the wall thickness can be tuned by the fabrication process. In this work SiNTs with comparable inner diameter to the PSi structure and a wall of about 10 nm are used (1). FePt nanoparticles (NPs) are deposited electroless inside the pores and the tubes, respectively whereat the molar ratio of Fe is varied. For this purpose a 3 component solution consisting of H2PtCl6, Fe(NO3)3 and citric acid is used, whereas the ratio of the components is modified.The varying magnetic response of the different composite systems, porous silicon and silicon nanotubes is investigated. PSi/FePt shows a higher coercivity and remanence than SiNTs/FePt and thus a higher hard magnetic performance. The variation of the coercivities between SiNTs/FePt and PSi/FePt is about 57%.Considering the FePt deposits with different molar ratio of Fe the coercivities vary in a range of 5% in the case of both template types. Comparing FePt loaded samples with Co loaded samples in all cases an increase of the coercivity and of the remanence is observed for FePt, whereat in the case of PSi as template material the increase is significantly stronger than in the case of SiNTs samples. Figure 1 shows the comparison of the hysteresis of PSi and SiNTs filled with FePt NPs.The influence of high temperatures on the nanocomposite samples is of interest, as well as the high temperature magnetic behavior. Therefore, beside low temperature and room temperature magnetic measurements, the magnetic behavior of the samples is investigated at high temperatures up to 1273 K.(1) K. Rumpf, et.al, ECS Transactions 98 (2020) 37

Magnetic properties of gadolinium and/or dysprosium substituted Sm–Co nanocomposite ribbons

The present study reported the influence of heavy rare-earth elements (Gd and/or Dy) on Sm-Co-based melt-spun ribbons. Microstructure and magnetic properties of Sm-Co-based (Sm1–xRExCo5) ternary and quaternary systems were investigated. The X-ray diffraction, Auger spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses reveal the presence of the 1:5H and 2:17R phases in the as-spun ribbons. A high-temperature magnetic measurement reports a Curie temperature (TC) at ∼825 and ∼869 K in Sm0.6Gd0.4Co5 (ribbon A) and Sm0.6Gd0.3Dy0.1Co5 (ribbon B), respectively. A low-temperature magnetic measurement on Sm0.6Gd0.3Dy0.1Co5 ribbons exhibits a type-2 SR (spin reorientation) behaviour at ∼72 K, which arises due to the presence of the DyCo5 phase. Room temperature magnetic measurements reveal that overall magnetic measurement (OMP) is about 24 and 29.9 for ribbons A and B, respectively. Consequently, the comparative investigations profess that ribbon B shows better magnetic performance due to Dy addition with reduced grain size. This observation indicates that the Gd and Dy substituted Sm–Co magnet can be a potential magnet for high-temperature applications.

Ce substituted NiCo[formula omitted] microspheres and nanoflakes: Comparison on magnetic features

NiCo2−xCexO4 (0.0 ≤ x ≤ 0.08) microspheres (MCs) and nanoflakes (NFs) were synthesized hydrothermally. X-ray diffraction analysis confirmed the cubic microstructure of all the samples. The microsphere and nanoflake morphologies of the samples have been confirmed by SEM, along with EDX, TEM and HR-TEM. The magnetic properties of the NiCo2−xCexO4 (0.0 ≤ x ≤ 0.08) MCs and NFs were investigated via magnetization measurements using a vibrating sample magnetometer. Room-temperature magnetization measurements revealed weak ferromagnetic behavior for both MC and NF samples. Low temperature magnetization measurements showed strong ferromagnetic behavior for the different samples. The magnetic parameters for both samples were found to differ substantially at a given temperature, which is accredited to the differences in the morphology of the MC-like and NF-like samples. Room-temperature magnetization measurements revealed antiferromagnetic or paramagnetic behavior for MC samples and weak ferromagnetic character for NF samples. It was also found that the magnetization magnitude decreased with increasing cerium dopant level, when compared to the host product. The changes in magnetization are linked to the effect of introduced cerium ions and their magnetic states, which could generate structural/morphological changes, changes in the size and surface lattice, redistribution of cations among the crystal lattices, changes in magnetic moment, etc.

Study of low-temperature magnetic properties of the antiferromagnetic topological insulator Sm-doped MnBi2Te4

MnBi2Te4 is the first discovered intrinsic magnetic topological insulator. It has great research significance and is related to new phenomena such as topological magneto-electric effect and quantum anomalous Hall effect (QAHE). We report first doping of rare-earth elements in MnBi2Te4 crystals. MnBi2Te4 crystalline samples with different Sm doping ratios were synthesized, and Sm atoms may enter the lattice and replace Mn atoms. Low-temperature magnetization measurements show that, in addition to the antiferromagnetic (AFM) transition of MnBi2Te4, some doped samples undergo small-scale ferromagnetic transitions at around 15 K. Doping furthermore reduces the magnetic field required for the transition to the canted AFM (CAFM) state and slightly increases the Néel temperature of the crystal. Our results suggest that doping rare-earth elements may be a feasible method for tuning the magnetism of MnBi2Te4 and for future applications of magnetic topological insulators.

Observation of c -axis magnetization at low temperatures in the weak ferromagnet FeBO3 reveals a spin-reorientation transition

The weak ferromagnet $\mathrm{Fe}{\mathrm{BO}}_{3}$ is well known for being a unique system for modeling and testing magnetic dynamics primarily due to relatively simple and localized magnetic structure and its interesting spin wave dynamics. At room temperature, it has slightly canted iron moments lying in the $a\text{\ensuremath{-}}b$ plane that result in a strong antiferromagnetic moment and a weak ferromagnetic moment, which results in pronounced ferromagnetic and antiferromagnetic spin modes. However, some previous studies have shown unusual low-temperature behavior that suggests a phase transition. By performing low-temperature magnetization measurements, both in bulk and on the mesoscale, we have observed a low-temperature magnetic texture in this material in which a large $c$-axis magnetization occurs. Magnetic fields along the $c$ axis as high as 1300 Oe were observed close to the sample's surface. This presents evidence for the onset of a Morin transition or another type of spin-reorientation phase transition wherein the ${\mathrm{Fe}}^{3+}$ moments would acquire a $c$-axis component to their canting below a critical temperature. The observation of this $c$-axis magnetization suggests that there is a different ground state in this material than has been previously expected and could be due to as yet unexplored intricacies of the Dzyaloshinskii-Moriya interaction.

Magnetic phase diagram in the three-dimensional triangular-lattice antiferromagnet Sr3CoTa2O9 with small easy-axis anisotropy

We report the results of low-temperature magnetization and specific heat measurements of ${\mathrm{Sr}}_{3}{\mathrm{CoTa}}_{2}{\mathrm{O}}_{9}$ powder, in which ${\mathrm{Co}}^{2+}$ ions with effective spin-1/2 form a uniform triangular lattice in the $ab$ plane. It was found that ${\mathrm{Sr}}_{3}{\mathrm{CoTa}}_{2}{\mathrm{O}}_{9}$ undergoes successive antiferromagnetic transitions at ${T}_{\mathrm{N}1}=0.97\phantom{\rule{4pt}{0ex}}\mathrm{K}$ and ${T}_{\mathrm{N}2}=0.79\phantom{\rule{4pt}{0ex}}\mathrm{K}$ at zero magnetic field. As the magnetic field increases, both ${T}_{\mathrm{N}1}$ and ${T}_{\mathrm{N}2}$ decrease monotonically. The obtained magnetic field vs temperature phase diagram together with a sharp magnetization anomaly at a saturation field of ${\ensuremath{\mu}}_{0}{H}_{\mathrm{s}}=2.3$ T indicates that ${\mathrm{Sr}}_{3}{\mathrm{CoTa}}_{2}{\mathrm{O}}_{9}$ is described as a spin-1/2 three-dimensional triangular-lattice antiferromagnet with a weak easy-axis anisotropy. We discuss the characteristics of the magnetic phase diagram, which approximates the phase diagram for the magnetic field perpendicular to the $c$ axis.

Studies on the effect of In3+ ion on magnetic and magneto caloric properties of polycrystalline TbMnO3

Polycrystalline Tb1−xInxMnO3 (x ​= ​0.0, 0.05, and 0.075) compounds, have been prepared using conventional solid state reaction method. Their structural, magnetic, and magnetocaloric properties are studied using the Powder X-ray diffraction, RT-Raman spectroscopy, low temperature magnetization measurements. The X-ray powder diffraction analysis reveals that these compounds crystallized in orthorhombic structure with space group (Pbnm). The structural analysis showed that the two lattice parameters (a, b) in the basal plane slightly decrease while the axial lattice parameter (c) remains unchanged with increase of In doping. Overall reduction in the cell volume indicates the substitution of In ions for Tb ions. A weak AFM ordering has been observed in the magnetic measurements for all the three compounds due to the ordering of Tb3+ moments. External magnetic field induced meta-magnetic transition for all the compounds. The maximum isothermal entropy change - ΔSMmax for the field value of 7 ​T was observed to be 8.72 ​J/Kkg,7.46 ​J/K kg and 7.07 ​J/K kg for x ​= ​0.0, 0.05, and 0.075 respectively.

Effect of Barium doping on structural and magnetic properties of Nickel Ferrite

The present study explores the impact of Barium (Ba) substitution on the structural, morphological, and magnetic properties of ultrafine Ni1-xBaxFe2O4 (0 ≤ x ≤ 1) nanoparticles synthesized by the cost-effective auto-combustion approach. Structural analysis of synthesized nanoparticles by X-ray diffraction pattern declares the transformation of Fd-3m symmetry to orthorhombic Bb21 m crystal structure. The increasing trend in volume due to the lattice expansion with the addition of Ba in NiFe2O4 is observed. In addition, the crystallite size is reduced from 35.07 to 30.69 nm due to the increase in Ba substitution. The morphology of nanoparticles confirmed by scanning electron microscopy (SEM) determines an increasing trend of grain size from 29 to 36 nm as a function of Ba doping. The room temperature hysteresis loops measured by a vibrating sample magnetometer (VSM) indicate that the magnetic coercivity increases as a function of Ba substitution and provides a maximum value of 3.5 kOe for BaFe2O4. However, saturation magnetization is maximum (∼40.7 emu/g) for NiFe2O4 and declines to a minimum value of ∼26.65 emu/g for BaFe2O4. Moreover, low-temperature magnetic measurements were estimated for BaFe2O4 through physical property measurement system (PPMS), where an increasing trend in coercivity (∼3.2–4.5 kOe), saturation magnetization (∼21–50 emu/g), and effective anisotropic magnetic constant (∼7.06 × 104–2.3 × 105 erg/g) was confirmed as the temperature decreases from 400 to 5 K.

London Dispersion Favors Sterically Hindered Diarylthiourea Conformers in Solution.

We present an experimental and computational study on the conformers of N,N′‐diphenylthiourea substituted with different dispersion energy donor (DED) groups. While the unfolded anti–anti conformer is the most relevant for thiourea catalysis, intramolecular noncovalent interactions counterintuitively favor the folded syn–syn conformer, as evident from a combination of low‐temperature nuclear magnetic resonance measurements and computations. In order to quantify the noncovalent interactions, we utilized local energy decomposition analysis and symmetry‐adapted perturbation theory at the DLPNO‐CCSD(T)/def2‐TZVPP and sSAPT0/6‐311G(d,p) levels of theory. Additionally, we applied a double‐mutant cycle to experimentally study the effects of bulky substituents on the equilibria. We determined London dispersion as the key interaction that shifts the equilibria towards the syn–syn conformers. This preference is likely a factor why such thiourea derivatives can be poor catalysts.

Mono- and binuclear copper(II) complexes with different structural motifs and geometries: Synthesis, spectral characterization, DFT calculations and superoxide dismutase enzymatic activity

Several new copper(II) mono- and binuclear complexes, [Cu(HL)(ClO4)(H2O)]CH3OH (1), [Cu(HL)(DMF)](ClO4)CH3OH (2), [Cu2(HL)2(pyrazine)](ClO4)2(3) and [Cu2(HL)2(4,4-bipy)(ClO4)2]2H2O (4) (HL = 4-bromo-2-(pyridine-2-ylhydrazonomethyl)-phenol, 4,4-bipy = 4,4-bipyridyl) have been synthesized and characterized by elemental analysis, FTIR, UV–vis and electron paramagnetic resonance (Epr) spectroscopy. Molecular structures of all complexes have been obtained using single crystal X-ray analysis. The geometry of copper(II) in 1 is distorted square pyramidal and distorted square planar in 2. In binuclear complexes each copper(II) centre has distorted square planar and distorted square pyramidal geometry in 3 and 4, respectively. The complexes 1–4 possess the self-assembled supramolecular structures via different molecular interactions (hydrogen bondings, CH ⋯π and π⋯π stacking interactions). The possible intermolecular interactions were explored using 3D Hirshfeld surface and related 2D fingerprint plots, spectroscopic properties were studied using UV–visible and electron paramagnetic resonance techniques. Optimized geometry, frontier molecular orbital (FMO) and natural bond order (NBO) analysis were performed using density functional theory (DFT) calculations. To predict the chemical reactivity of complexes some global reactivity descriptors (chemical potential μ, electronegativity χ, hardness η and electrophilicity index ω) have been evaluated using DFT. The low temperature magnetic susceptibility measurements of binuclear complexes have been obtained predicts the magnetic exchange coupling value (J) by variable temperature measurements. The magnetic exchange coupling value (J) obtained are −8.1 and −2.4 cm−1 for 3 and 4, respectively. The superoxide dismutases (SOD) of all complexes were measured using NBT assay method. The complexes show moderate superoxide dismutase (SOD) mimetic activity.

Preparation and Characterization of Nanosized Substituted Perovskite Compounds with Orthorhombic Structure

In this work, five substituted perovskite such as (Gd0.9Sr0.1) Mn0.8Co0.2O3, Tb0.8Sr0.2FeO3, Gd0.6Sr0.4RuO3, SrCe0.95Y0.05O3, and Mn0.6Co0.4SnO3 were synthesized by tartrate and hydroxide precursor method. The resulting samples were characterized by inductively coupled plasma spectroscopy, energy dispersive X-ray analysis, infrared spectroscopy, thermal analysis, X-ray powder diffraction, transmission electron microscope (TEM), selected field of electron diffraction (SAED), d.c. electrical conductivity, Hall effect, dielectric measurements, and low-temperature magnetization measurements. The X-ray diffraction pattern for all compounds was indicated the formation of single-phase perovskite with orthorhombic structure except Tb0.8Sr0.2FeO3 and Mn0.6Co0.4SnO3 perovskite. These compounds showed a cubic and rhombohedral structure, respectively. The lattice parameter and the unit cell volume slightly decreased as ionic radii decrease in agreement with the lanthanide contraction. The average size of cation ˂ RA ˃, mismatch factor (σ2), and tolerance factor (t) gives the combined effects of disorder and inhomogeneity in these compounds. The average particle size determined from TEM was in the range of 22 to 77 nm for all compounds. The temperature dependence of electrical conductivity for all compounds showed a definite break in 500 K to 610 K. except the Gd0.6Sr0.4RuO3 compound, which corresponds to semiconducting behavior. While the Gd0.6Sr0.4RuO3 sample shows a metallic-like semiconductor. The thermoelectric power and Hall effect measurements for all compounds were n-type semiconductivity except the SrCe0.95Y0.05O3 compound. It showed p-type semiconductivity. The frequency dependence of the dielectric constant and dielectric loss in these substituted perovskites were discussed using the Maxwell-Wagner model. Magnetic studies showed that the thermo-magnetic irreversibility for all compounds.

Slow Magnetic Relaxation in {[CoCxAPy)] 2.15 H2O}n MOF Built from Ladder-Structured 2D Layers with Dimeric SMM Rungs.

We present the magnetic properties of the metal-organic framework {[CoCxAPy]·2.15 H2O}n (Cx = bis(carboxypropyl)tetramethyldisiloxane; APy = 4,4′-azopyridine) (1) that builds up from the stacking of 2D coordination polymers. The 2D-coordination polymer in the bc plane is formed by the adjacent bonding of [CoCxAPy] 1D two-leg ladders with Co dimer rungs, running parallel to the c-axis. The crystal packing of 2D layers shows the presence of infinite channels running along the c crystallographic axis, which accommodate the disordered solvate molecules. The Co(II) is six-coordinated in a distorted octahedral geometry, where the equatorial plane is occupied by four carboxylate oxygen atoms. Two nitrogen atoms from APy ligands are coordinated in apical positions. The single-ion magnetic anisotropy has been determined by low temperature EPR and magnetization measurements on an isostructural compound {[Zn0.8Co0.2CxAPy]·1.5 CH3OH}n (2). The results show that the Co(II) ion has orthorhombic anisotropy with the hard-axis direction in the C2V main axis, lying the easy axis in the distorted octahedron equatorial plane, as predicted by the ab initio calculations of the g-tensor. Magnetic and heat capacity properties at very low temperatures are rationalized within a S* = 1/2 magnetic dimer model with anisotropic antiferromagnetic interaction. The magnetic dimer exhibits slow relaxation of the magnetization (SMM) below 6 K in applied field, with a τlf ≈ 2 s direct process at low frequencies, and an Orbach process at higher frequencies with U/kB = 6.7 ± 0.5 K. This compound represents a singular SMM MOF built-up of Co-dimers with an anisotropic exchange interaction.