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Abstract: The influence of CuFe2O4 nanoparticle doping on superconducting properties of Fe-sheated MgB2 wires has been studied. The wires containing 0, 3 and 7.5wt.% of monodisperse superparamagnetic nanoparticles (∼7nm) were sintered at 650°C or 750°C for 1 hour in the pure argon atmosphere. X-ray diffraction patterns of doped samples showed very small maxima corresponding to iron boride and an increase in the fraction of MgO phase indicating some interaction of nanoparticles with Mg and B. Both magnetic and transport measurements (performed in the temperature range 2–42K and magnetic field up to 16 T) showed strong deterioration of the superconducting properties upon doping with CuFe2O4. The transition temperatures, Tc, of doped samples decreased for about 1.4K per wt.% of CuFe2O4. Also, the irreversibility fields Birr(T) decreased progressively with increasing doping. Accordingly, also the suppression of Jc with magnetic field became stronger. The observed strong deterioration of superconducting properties of MgB2 wires is at variance with reported enhancement of critical currents at higher temperatures (determined from magnetization) in bulk MgB2 samples doped with Fe3O4 nanoparticles. The probable reason for this discrepancy is briefly discussed [Copyright &y& Elsevier]

Abstract: Ferrihydrite (FH) nanoparticles were synthesised and subjected to γ-irradiation in the form of FH-ethanol suspension. The dose rate of γ-radiation was ∼16kGy/h and the samples were irradiated to doses of up to 2590kGy. γ-irradiation of FH-ethanol suspensions did not cause the transformation of FH to any of the other iron oxide phases. Likewise, neither the Mössbauer and FT-IR spectroscopy nor the quantitative analysis using Energy Dispersive X-ray Spectroscopy gave any evidence of structural changes of FH upon γ-irradiation. C, H analysis showed that the C concentration in FH gradually increased with dose and was higher in γ-irradiated FH samples than in non-irradiated FH sample. This finding suggested that carbon in FH originated from ethanol degradation. The H concentration in FH gradually increased to the dose of up to 340kGy and then slightly decreased. Magnetic measurements showed a progressive decrease in magnetisation with an increase in γ-irradiation. The results of magnetic measurements and C, H analysis suggested the carbonisation of FH surface. It was supposed that γ-irradiation of FH-ethanol suspension reductively decomposed ethanol thus generating unsaturated hydrocarbons and acetylides, which in turn formed a conjugate iron complex, thus carbonating the FH surface. The carbonisation of the FH surface prevented FH transformation to other iron oxide phases. [Copyright &y& Elsevier]

The scope of this article is to report very detailed results of the measurements of magnetic relaxation phenomena in the new Cu0.5Fe2.5O4 nanoparticles and known CuFe2O4 nanoparticles. The size of synthesized particles is (6.5±1.5) nm. Both samples show the superparamagnetic behaviour, with the well-defined phenomena of the blocking of magnetic moment. This includes the splitting of zero-field-cooled and field-cooled magnetic moment curves, dynamical hysteresis, slow quasi-logarithmic relaxation of magnetic moment below blocking temperature. The scaling of the magnetic moment relaxation data at different temperatures confirms the applicability of the simple thermal relaxation model. The two copper-ferrites with similar structures show significantly different magnetic anisotropy density and other magnetic properties. Investigated systems exhibit the consistency of all obtained results. [Copyright &y& Elsevier]

Abstract: The effect of the incorporation of Ir3+ ions on the properties of α-Fe2O3 formed by dehydroxylation of α-FeOOH was investigated using X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), 57Fe Mössbauer, UV–Vis–NIR and FT-IR spectroscopies, SQUID magnetometer, field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray spectroscopy (EDS). Pure and Ir-doped hematite samples were obtained by heating of pure and Ir-doped goethites (α-FeOOH) formed by precipitation from mixed Fe(III)–Ir(III) chloride solutions in a highly alkaline medium. The incorporation of Ir3+ ions into the α-Fe2O3 structure led to changes in unit-cell dimensions, crystallinity, particle size and shape, as well as changes in the magnetic, infrared and UV–Vis properties. An increase in the temperature of the Morin transition with an increase in Ir-doping was observed by Mössbauer spectroscopy and magnetic measurements. [Copyright &y& Elsevier]

Graphical abstract Highlights • Effect of the reaction temperature on structural and magnetic properties. • Prevailing antiferromagnetic interactions leading to the non-magnetic ground state. • Magneto-structural correlations in dicubane Ni(II) complexes. Abstract The two red centrosymmetric Ni(II) tetrameric complexes with defective double-cubane core, [Ni 2 L 2 (H 2 O)] 2 ·0.75 CH 3 OH (1) and [Ni 2 L 2 (CH 3 CN)] 2 (2) (H 2 L = N -(2-hydroxy-5-methylphenyl)-salicylideneimine), have been isolated and magnetically characterized, emphasizing the effect of the reaction temperature on structural and magnetic properties of isolated complexes. Prevailing antiferromagnetic interactions in the complexes are observed leading to the non-magnetic ground state. Comparation with the known magneto-structural correlations in nickel cubane and dicubane complexes is discussed. [ABSTRACT FROM AUTHOR]

Pure and Er-doped hematite (α-Fe 2 O 3) nanorods were prepared by a two-step method involving hydrothermal synthesis and calcination of pure and Er-doped goethite (α-FeOOH) nanorods. Substitution of Fe3+ by Er3+ in the crystal structure of hematite caused morpho-structural changes such as expansion of the unit cell and gradual shortening and rounding of hematite nanorods towards formation of nanoellipsoids. These changes induced modification of magnetic and optical properties suggesting the possibility of a systematic control of physical properties via rare earth substitution. A decrease in the hyperfine magnetic field, coercive field and Morin transition temperature, as well as an increase of the magnetic susceptibility and a narrowing of the optical band gap were observed by substitution. Intimate mechanisms related to the formation of more and more defect-like hematite phases with decreased temperatures for the transition to the low temperature antiferromagnetic phase at increased doping level were evidenced via temperature dependent Mössbauer spectroscopy. • Fairly uniform Er-doped hematite nanorods and nanoelipsoids were prepared. • The particle shape depended on the molar fraction of erbium. • Temperature of the Morin transition decreased by Er doping. • Magnetic susceptibility increased by Er doping due to uncompensated spins. • The optical band gap slightly narrowed by Er doping. [ABSTRACT FROM AUTHOR]

The results indicating magnetic flux pinning in MgB 2 wires doped with three types of magnetic nanoparticles (MNP) are reported. The magnetic state of MNPs, both as-prepared and inside the MgB 2 core, was determined with magnetization and ac susceptibility measurements. The competition between detrimental influence of doping (reduced connectivity, pair breaking) and enhanced flux pinning leads to deterioration of electromagnetic properties of doped wires at high MNP content, whereas light doping causes an enhancement of critical current density, J c , and/or irreversibility field, B irr , for all our MNPs. For Ni and dextrin coated NiFe 2 O 4 MNPs the enhancement of J c was comparable to that achieved with the best nonmagnetic dopands. Detailed analysis indicates the contribution of magnetic flux pinning including the matching effects in flux pinning on MNPs. [ABSTRACT FROM AUTHOR]

Abstract: Magnetic properties of single crystals of the heterometallic complex [Cu(bpy)3]2[Cr(C2O4)3]NO3·9H2O (bpy=2,2′-bipyridine) have been investigated. From the recorded EPR spectra, the spin-Hamiltonian parameters have been determined. The magnetization measurements have shown magnetic anisotropy at low temperatures, which has been analysed as a result of the zero-field splitting of the CrIII ion. By fitting the exactly derived magnetization expression to the measured magnetization data, the axial zero-field splitting parameter, D, has been calculated. Comparing to the EPR measurements, it has been confirmed that D can be determined from the measurements of the macroscopic magnetization on the single crystals. [Copyright &y& Elsevier]

Abstract: Two novel compounds of the formulae [{Cu(phen)2}2(μ-C2O4)][Cu(phen)2(μ-C2O4)NbO(C2O4)2]2 ·8H2O (1) and [{Cu(bpy)2}2(μ-C2O4)][Cu(bpy)2(μ-C2O4)NbO(C2O4)2]2 ·0.5bpy·7H2O (2) (phen=1,10-phenanthroline, bpy=2,2′-bipyridine) have been prepared and characterized by single crystal X-ray diffraction, IR spectroscopy and magnetic susceptibility measurements. The molecular structure of both 1 and 2 consists of a discrete CuIICuII oxalate-bridged dinuclear [{Cu(L)2}2(μ-C2O4)]2+ cation (A unit) and two CuIINbV oxalate-bridged dinuclear [Cu(L)2(μ-C2O4)NbO(C2O4)2]− anions (B units) (L=phen, bpy). In 1 a crystallographic inversion centre is located in the middle of the oxalate bridge of the A unit, whereas in 2 an analogous inversion centre is missing. In the A units the copper(II) atoms adopt a tetragonally elongated octahedral coordination with the equatorial planes being perpendicular to the mean planes of the oxalate bridge and parallel to each other. In both structures, similar one-dimensional motifs are generated through the ligand stacking interactions, with a difference that one free bipyridine molecule, present in 2, intercalates into one of the motifs. It is shown that the phenanthroline ligand, due to its ability of stacking through the central aromatic ring, causes longer intermolecular Cu⋯Cu distances than the bipyridine ligand. The magnetic susceptibility measurements (1.8–290K) show the ferromagnetic exchange interaction between the copper(II) atoms in the A units of both compounds, with J =+5.9cm−1 and +7.9cm−1 for 1 and 2, respectively (J – the exchange parameter in the isotropic spin Hamiltonian H INT =−J S 1 · S 2). [Copyright &y& Elsevier]

Iron(III) chloride deaerated alkaline aqueous colloidal solutions in the presence of 2-propanol and DEAE-dextran (diethylaminoethyl-dextran hydrochloride) were γ-irradiated with doses of 36 and 130 kGy. The dose rates were ~7 and ~31 kGy h−1. The extremely stable aqueous suspension of substoichiometric Fe 2.83 O 4 magnetite nanoparticles ~4.7 nm in size were formed at a dose rate of ~7 kGy h−1 and at a dose of 36 kGy. At a dose of 130 kGy the anisotropic δ-FeOOH magnetic discs with a diameter of ~256 nm and thickness of ~40 nm were formed. Each disc has a substructure consisting of approximately eighteen laterally stacked thin nanodiscs of about 2.2 nm in thickness. At a higher dose rate of ~31 kGy h−1and at a dose of 36 kGy, XRD revealed the presence of highly substoichiometric Fe 2.75 O 4 magnetite, whereas TEM analysis revealed the presence of ~4.3 nm magnetite nanoparticles along with rod-shaped γ-Fe 2 O 3 nanoparticles. The values of isomer shift in Mössbauer spectra of about 0.33 mm s−1 showed that all Fe(II) in substoichiometric magnetites oxidized to Fe(III) one month after synthesis. At high dose and dose rate, the rolled rod-like δ-FeOOH magnetic nanoparticles were formed having the diffraction patterns with streaks, which are characteristic of tubular structures. The magnetic measurements showed exceptional intrinsic room-temperature magnetic properties of both δ-FeOOH nanostructures with the Curie temperature above 300 K. In order to ascertain the formation of Fe(II) intermediate products prior to their oxidation, γ-irradiated samples were isolated by admixing glycerol. The amounts of Fe(II) in glycerol-isolated solid samples were determined using Mössbauer spectroscopy. Carbonate Green Rust I [GR(CO 3 2−)] and Fe(OH) 2 intermediate phases were confirmed by XRD and Mössbauer spectroscopy. The amounts of Fe2+ in the acidified solutions containing dissolved γ-irradiation ferrous products were determined using the potassium permanganate titration. The amounts of Fe2+ were 68.9% and 96.1% at doses of 36 and 130 kGy, respectively. Thus, at a dose of 130 kGy the radiolytically generated Fe(OH) 2 , after coming in contact with oxygen and CO 2 from the air, topotactically oxidized to GR(CO 3 2−) and further to δ-FeOOH without any structural changes. The lower dose rate (~7 kGy h−1) favored the δ-FeOOH nanodisc morphology, whereas the higher dose rate (~31 kGy h−1) favored the formation of tubular rod-like δ-FeOOH nanoparticles. Unlabelled Image • γ-Irradiation can reduce Fe(III) up to Fe(OH) 2 in the presence of DEAE-dextran. • The intermediate phases Fe(OH) 2 and GR(CO 3 2−) were captured by admixing glycerol. • Magnetite NPs 4.7 nm in size formed at dose rate of 7 kGy h−1 and at a dose of 36 kGy. • At a dose of 130 kGy the δ-FeOOH nanodiscs or δ-FeOOH tubular rod-like NPs formed. • Synthesized δ-FeOOH has unique magnetic properties with Curie temperature above 300 K. [ABSTRACT FROM AUTHOR]