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Cobalt(II)-Nicotinamide had been synthesized mole ratio in 1 : 2 of metal to the ligand in methanol. The complex was characterized by atomic absorption spectrophotometer (AAS), conductometer, UV-Vis spectrophotometer, MSB (magnetic susceptibility balance) and FT-IR spectrophotometer. The result of AAS showed that cobalt(II) in the complex was 14,40%. The molar conductivity showed that the complex was 2 to 1 electrolyte. UV-Vis spectra appeared a transition peak of third transition 4T1g(F) → 4T1g(P). The momen magnetic showed that the complex was paramagnetic. The infrared spectral indicate that groups of primary N-H and carbonyl were coordinated to the center ion of Co(II). The complex formula was estimated as [Co(Nicotinamide)2(H2O)2]Cl2 and probably octahedral.

Coordination reaction of the stable ground triplet biradical biphenyl-3,5-diyl bis(tert-butyl nitroxide) and [Gd(hfac)3(H2O)2] unexpectedly gave complexes containing a dimerized diamagnetic ligand via a [3+3] cycloaddition of the benzene rings (hfac = 1,1,1,5,5,5-hexafluoropentane-2,4-dionate). To avoid such dimerization, we introduced a bulkier substituent into the ligand; namely, a new ground triplet biradical 5-mesityl-1,3-phenylene bis(tert-butyl nitroxide) was applied to this complexation scheme. However, an unexpected complex was again obtained in a different way, and the magnetic study revealed that the novel ligand involved was diamagnetic. The crystallographic analysis of the product clarified isomerization from the paramagnetic ligand to a diamagnetic N-tert-butylaminoquinone imine N-oxide ligand as a result of disproportionation from two open-shell nitroxide groups to closed-shell groups, an amine and a nitrone. The present paper reports the first structural evidence for a diamagnetic isomer of m-phenylene-bridged bisnitroxde compounds.

Werthamer, Helfand, and Hohenberg (WHH) model is applied to the measured upper critical magnetic fields of Ni-and Co-doped pnictide bulk superconductors. This approach incorporates both orbital and paramagnetic effects in the upper critical field’s temperature dependence. The relative importance of both the orbital and paramagnetic effects in the suppression of the superconductivity is described by the Maki parameter. In most superconductors, the Maki parameter is usually much less than unity suggesting that the influence of the paramagnetic effect is small. However, in materials with heavy electron effective mass, in which the Fermi energy is small, or in layered materials in a magnetic field parallel to the layers, the Maki parameter can be larger than unity. This is the case for our bulk pnictides. By fitting the measured temperature dependence of the upper critical field, we derive the Maki parameter and the spin orbit scattering constant and examine the correlation between the Maki parameter, the spin orbit scattering constant, and the reduced upper critical field for our curve fits vs. temperature. The obtained Maki parameters indicate that the Zeeman pair breaking dominates over the orbital pair breaking and spin-paramagnetic pair-breaking effect is significant. At the same time, our spin orbit scattering constants indicate that spin-orbit scattering needs to be also included in description of the Hc2(T) data in these materials.

New complexes doubly chelated with two paramagnetic ligands, [MII(6bpyNO)2](ClO4)2•xCH3OH [M = Mn (x = 0.53), Ni (x = 1); 6bpyNO = 2,2’-bipyridin-6-yl tert-butyl nitroxide] were prepared. The X-ray crystallographic analysis revealed the isomorphous [M(6bpyNO)2]2+ structure. The magnetic measurements clarified antiferromagnetic 2JMn-rad/kB = –112(2) K and ferromagnetic 2JNi-rad/kB = +384(4) K, based on a symmetrical model H = –2JM-rad(SM•Srad1+SM•Srad2). The coupling mechanism is explained in terms of the 3d5 and 3d8 spin configurations leading to the dπ-pπoverlap in the Mn complex and the dσ-pπ orthogonal arrangement in the Ni complex along the metal-radical bonds.

A theory of high-energy optical conductivity of La0.7Ca0.3MnO3 has been proposed previously. The proposed theory works to explain the temperature-dependence of the optical conductivity for the photon energy region above ∼0.5 eV for up to ∼22 eV, but fails to capture the correct physics close to the dc limit in which metal-insulator transition occurs. The missing physics at the low energy has been acknowledged as mainly due to not incorporating phonon degree of freedom and electron-phonon interactions. In this study, we aim to complete the above theory by proposing a more complete Hamiltonian incorporating additional terms such as crystal field, two modes of Jahn-Teller vibrations, and coupling between electrons and the two Jahn-Teller vibrational modes. We solve the model by means of dynamical mean-field theory. At this stage, we aim to derive the analytical formulae involved in the calculation, and formulate the algorithmic implementation for the self-consistent calculation process. Our final goal is to ...

In the present work, polycrystalline Sm0.55Sr0.45MnO3 thin films were prepared on LSAT (001) single crystal substrates by ultrasonic nebulized spray pyrolysis technique. The X-ray diffraction θ-2θ scan reveals that these films (i) have very good crystallinity, (ii) are oriented along out-of-plane c-direction, and (iii) are under small tensile strain. The impact of oxygen vacancy results into (i) higher value of paramagnetic insulator (PMI) to ferromagnetic metal (FMM) transition temperature, i.e., TC/TIM, (ii) sharper PMI-FMM transition, (iii) higher value of magnetization and magnetic saturation moment, and (iv) higher value of magnetoresistance (∼99%). We suggest here that oxygen vacancy favors FMM phase while oxygen vacancy annihilation leads to antiferromagnetic-charge ordered insulator (AFM-COI) phase. The observed results have been explained in context of phase separation (PS) caused by different fractions of the competing FMM and AFM-COI phases.

The temperature field developed by the magnetic nanoparticles injected directly within malignant tissues provides precious information about the main parameters which influence their heating mechanisms. This paper analyses the temperature field induced within a tumoral tissue by the Fe - Cr - Nb - B and magnetite systems, when an external time - dependent magnetic field is applied. An analytical temperature model which predicts the temperature in a tumoral tissue was developed. The particles with a lognormal size distribution were considered. The heat generation by Neel and Brown relaxations was modeled using the thermal and magnetic properties of the Fe - Cr - Nb - B particles experimentally determined. Fe - Cr - Nb - B magnetic systems have a particular behavior with the frequency and amplitude of the AC magnetic field. The temperature field can be controlled by tuning of the magnetic field parameters. As a result of their magnetic and thermal properties, these systems can be used for the magnetic hyper...

Here in this paper, we report how the influence of polyethylene glycol (PEG-4000) and silica on crystal structure and magnetic properties of MgFe 2 O 4 nanoparticles synthesized by the co-precipitation method. X-ray Diffraction (XRD) analysis showed that the particle’s size of the MgFe 2 O 4 around 10.5 nm before coating, and became 5.2 nm after PEG-4000 coating and 18.8 nm after silica coating. The new phase appeared after MgFe 2 O 4 was coated by PEG-4000 and silica, ie α-Fe 2 O 3 which is antiferromagnetic, SiO 2 and γ-FeO(OH) which is paramagnetic. The second phase sample is lowered response to the external field. TEM Morphology analysis on PEG 4000 coated nanoparticles showed that the particles become more round, more dispersive, and less aglomerated. The magnetic hysteresis loops investigated with Vibrating Sample Magnetometer (VSM) indicated that coercivity of MgFe 2 O 4 was 120,7 Oe, and then decreased after coating to 40,9 Oe and 34,7 Oe for coating with PEG-4000 and silica, respectively. At 15 kOe, magnetization value decreased from 2.69 emu/g to 0.96 emu/g after PEG-4000 coating and increased 2.82 emu/g after silica coating. Based on the result it can be concluded that coating by PEG-4000 and silica influence the magnetic properties of MgFe 2 O 4 nanoparticles.

We have proposed tert-butyl 2-pyridyl nitroxide radicals as a promising paramagnetic chelating ligand, where the direct radical-metal bond leads to strong magnetic interaction. We successfully synthesized and isolated PyBN derivatives (pyridine-2,6-diyl bis(tert-butyl nitroxides)). The molecular and crystal structures of the target biradicals, MesPyBN, AntPyBN and tBuOPyBN were determined from the X-ray crystal structure analysis, which possess mesityl, 9-anthryl and tert-butoxy groups at the 5-position of the pyridine ring, respectively. The ground triplet state was characterized by means of SQUID susceptometry for each compound. On heating, the χmT values of all the PyBN derivatives increased and reached a plateau at ca. 1.0 cm3 K mol−1 at 300 K. It implies that biradicals behaved as triplet molecules even at room temperature, or 2J/kB >> 300 K. From the decay monitored in solution electron-spin resonance spectroscopy, MesPyBN was the most persistent, while tBuOPyBN was the most reactive, of the three.

In this work, Nd0.7Ba0.3MnO3 was synthesized via cryo-milling method to investigate the effect of calcination temperature on the structure, microstructure, magnetic and electrical properties. XRD analysis revealed all samples can be indexed to orthorhombic structure systems with Imma space group accompany with some minor phases of Mn2O4 and BaMnO3. FESEM analysis confirmed that a slight increase in the grain size from 117.4 nm (600°C), 119.5 nm (700°C), 121.0 nm (800°C), 123.1 nm (900°C) to 138.4 nm (1000°C) was observed when different calcination temperature was applied. Four Point Probe measurements showed that all samples are in paramagnetic insulating region and TMIT is lower than 20K. Resistivity increase when grain size reduces due to increase of effective grain boundary that weakens the electron hopping process via double exchange mechanism. Beside, a drastic increase of resistivity also observed due to present of minor secondary phase (BaMnO3) in sample C9.

The incorporation of magnetic field sensors into eddy current probes can result in novel probe designs with unique performance characteristics. One such example is a recently developed electromagnetic probe consisting of a two-channel magnetoresistive sensor with an embedded single-strand eddy current inducer. Magnetic flux leakage maps of ferrous materials are generated from the DC sensor response while high-resolution eddy current imaging is simultaneously performed at frequencies up to 5 megahertz. In this work the design and optimization of this probe will be presented, along with an application toward analysis of sensory materials with embedded ferromagnetic shape-memory alloy (FSMA) particles. The sensory material is designed to produce a paramagnetic to ferromagnetic transition in the FSMA particles under strain. Mapping of the stray magnetic field and eddy current response of the sample with the hybrid probe can thereby image locations in the structure which have experienced an overstrain condition. Numerical modeling of the probe response is performed with good agreement with experimental results.

Detailed 57Fe M\"ossbauer spectroscopy measurements on superconducting NaFeAs powder crystals have been performed. The 57Fe spectra recorded in the paramagnetic temperature range (T > TN \approx 46 +/- 2 K) were discussed supposing Fe2+ ions are located in distorted tetrahedral (FeAs4) polyhedra. Our results reveal that the structural transition (TS \approx 55 K) has a weak effect on the electronic structure of iron atoms while the development of the antiferromagnetic order (T =< TN) induces a redistribution of the charge at 57Fe nuclei. In the low-temperature range, the spectra show a diffuse resonance absorption structure which evidences for the existence of a continuous distribution of hyperfine fields HFe at 57Fe nuclei. The shape of these spectra can be related to the formation of a microdomain structure or phase separation. Analysis of the resulting distributions p(HFe) has shown that the M\"ossbauer spectra give consistent and physically reasonable 57Fe hyperfine parameters over the whole temperature range., Comment: This paper has been withdrawn by the author due to conflict of interests

Magnetic nanoparticles have been of continuous interest, in part, because of the surface effects on the magnetic properties and, in particular, because of their possible use in future magnetic storage devices. In this contribution we discuss the results of ab initio calculations for tiny magnetic transition metal clusters up to ∼103 atoms and show the variation of the magnetic moments and magnetic anisotropy as a function of the cluster size, morphology and kind of transition metal atoms. Since the ab initio calculations show that the magnetic moments of the clusters have rather localized character, we have also considered quantum Heisenberg models of spin‐1/2 and spin‐1 clusters. The exact diagonalization of these models provide some supplementary informations to the first‐principles calculations regarding correlation functions and thermodynamic properties.

Individual InAs/GaAs quantum dots (QDs) are studied with micro‐photoluminescence in the presence of an applied external magnetic field. Attention is focused on the redistribution between the spectral lines of a single QD observed at increased external magnetic field when the magnetic field is applied parallel to the growth direction (Faraday geometry). The effect is shown to be transport related as the electron drift velocity in the QD‐plane is decreased by the applied magnetic field and this affects the probability for electron capture into the QD.

Structural and magnetic properties of manganese (Mn)‐doped silicon carbide (SiC) are investigated. Two Mn‐doping methods of ‘thermal diffusion’ and ‘ion implantation’ are employed using 4H (hexagonal)‐ and 3C (cubic)‐SiC homoepitaxial wafer as the host material. In the case of 4H‐SiC doped using the thermal diffusion method, the extended X‐ray absorption fine structure (EXAFS) analysis suggests that most Mn atoms are incorporated on the interstitial site in the 4H‐SiC lattice, and a paramagnetic behavior is observed in the magnetization measurement. For the Mn‐implanted 3C‐SiC, on the other hand, we detect ferromagnetic behaviors and a Curie temperature is found to reach to 245 K.

The triplet superconductivity in $UGe_2$ and $URhGe$ coexists with itinerant ferromagnetism such that in the pressure-temperature phase diagram the whole region occupied by the superconducting state is situated inside a more vast ferromagnetic region. In the same family metal UCoGe the pressure dependent critical lines T_{Curie}(P) and T_{sc}(P) of the ferromagnet and the superconducting phase transitions intersect each other. The two-band multidomain superconducting ferromagnet state arises at temperatures below both of these lines. Here I describe the symmetry and the order parameters of the paramagnet as well of the multidomain ferromagnet superconducting states. The Josephson coupling between two adjacent ferromagnet superconducting domains is discussed., 6 pages, 1 figure, published in the Proceedings of L.D.Landau 100 years Memorial Conference

International audience; Adding an extra nucleon having a definite K-value to an axially symmetrical even-even core generates a breaking of the time-reversal symmetry. Within the Skyrme-Hartree-Fock approach the effects of the time-odd mean-field terms resulting from the presence of non-vanishing current and spin-vector densities are investigated. In this preliminary study, pairing correlations are not taken into account. The associated removal of the Kramers degeneracy is interpreted in terms of diamagnetic/paramagnetic types of polarization of the even-even core in the field of an odd particle. This general approach is illustrated here by calculations in the region of light fragments of heavy (e.g. actinide) nuclei.

Transport, magnetic and thermal properties at high magnetic fields (H) and low temperatures (T) of the heavy fermion compound CeAuSb2are reported. At H=0 this layered system exhibits antiferromagnetic order below TN= 6K. Applying B along the inter-plane direction, leads to a continuous suppression of TNand a quantum critical point at Hc≅ 5.4 T. Although it exhibits Fermi liquid behavior within the Neel phase, in the paramagnetic state the fluctuations associated with Hcgive rise to unconventional behavior in the resistivity (sub-linear in T) and to a TlnT dependence in the magnetic contribution to the specific heat. For H > Hc, and low T the electrical resistivity exhibits an unusualT3-dependence. © 2006 American Institute of Physics.

The optical absorption spectrum of EuTe epitaxial layers grown by molecular beam epitaxy was studied at low temperatures and high magnetic fields, using circularly polarized light. At high magnetic fields a narrow line (width 41 meV) emerges at the low energy side of the absorption threshold. The line shows a huge displacement with magnetic field and is attributed to a magnetic exciton. The emergence of this line has a strong effect on the Faraday rotation, which becomes strongly non‐linear.

Composite hadronic states exhibit interesting properties in the presence of very intense magnetic fields, such as those conjectured to exist in the vicinity of certain astrophysical objects. We discuss three scenarios. (i) The presence of vector particles with anomalous magnetic moment couplings to scalar particles, induces an instability of the vacuum. (ii) A delicate interplay between the anomalous magnetic moments of the proton and neutron makes, in magnetic fields $B\ge 2\times 10^{14}$ T, the neutron stable and for fields $B\ge 5\times 10^{14}$ T the proton becomes unstable to a decay into a neutron via $\beta$ emission. (iii) In the unbroken chiral $\sigma$ model magnetic fields would be screened out as in a superconductor. It is the explicit breaking of chiral invariance that restores standard electrodynamics. Astrophysical consequences of all these phenomena are discussed., Comment: Submitted to the 26th International Conference on High Energy Physics (using macropackage REVTEX II), 10 pages

We have extended the Ramirez‐Falicov model of the α‐γ phase transition of cerium, allowing for a field‐induced or spontaneous splitting of the bands and of the six‐fold degenerate 4f level. To this end, we had to introduce two new parameters in the theory to take account of conduction electron‐f electron and conduction electron‐conduction electron exchange. The value of the latter can be estimated from the low‐temperture susceptibility of α cerium, for the former an upper limit can be found on the basis of the phase diagram. We find the effect of presently available magnetic fields on the α‐γ transition temperature in cerium to be negligible according to this theory. With higher values (not appropriate to cerium) for the conduction electron‐f electron exchange parameter, the model shows first and second order transitions to a ferromagnetic γ phase. The relative stability of this phase with respect to the α phase is higher than that of the paramagnetic γ phase; under certain circumstances there is no direct paramagnetic γ→α transition.

Neutron powder diffraction analysis and singel‐crystal studies of TbB4 indicate that this compound is isostructural with ErB4 and DyB4 but has a different magnetic structure. The magnetic moments of the Tb atoms appear to lie in mixed antiferromagnetic domains of approximately [301] and [031] orientation.

Europium telluride crystallizes in the NaCl structure and is antiferromagnetic with a Neel temperature TN of 9.6 K. We have used the 35.5 keV Mo/ssbauer transition in Te‐125 to examine the nature of the spontaneous magnetic moment which has been observed in conducting samples below TN. At 80 K the Mossbauer resonance spectrum consisted of a single absorption line comparable in width with the spectrum of nonmagnetic cubic ZnTe, indicating the absence of a significant quadrupole splitting at this temperature. At 4.2 K the line‐width increased by a factor of 1.5, which is equivalent to a single magnetic hyperfine field at the Te sites of about 73 kOe. The line showed gradual broadening with increasing external longitudinal magnetic field up to 70 kOe at 4.2 K. These observations are consistent with the magnetization measurements as well as with recent spin‐echo NMR experiments showing resonances which may be attributed to Te‐125. We conclude from the shape of the Mossbauer line that the broadening observed at 4.2 K is most likely due to a single magnetic hyperfine field of magnitude 73 kOe acting at the Te sites. An applied magnetic field H

The dependence of the elastic constants c11 and c33 on temperature and applied magnetic field has been measured for single‐crystal dysprosium in its paramagnetic phase, in an effort to determine certain magnetoelastic coupling constants. This work was motivated by a theoretical treatment of magnetoelastic phenomena of Southern and Goodings. Similar measurements for the case of terbium have been reported by Salama et al, but the present work includes magnetostrictive corrections neglected by these authors. The values obtained for the magnetoelastic coupling constants of dysprosium, following the theory of Southern and Goodings, are considerably larger than expected; those estimated from the static magnetostriction results of Clark et al are smaller by a factor of about 20. A possible reason for this large difference between the statically and dynamically determined values for the magnetoelastic coupling constants may lie in the assumption by Southern and Goodings that the principal magnetoelastic contribut...

The NaCl‐structured compound DySb, which in zero field transforms abruptly at TN?9.5 K to a Type‐II antiferromagnetic (A) state with a nearly tetragonal lattice distortion, was previously found to exhibit rapid field‐induced changes in magnetization at 1.5 K. The field‐induced transitions in a DySb crystal have been studied by neutron diffraction and magnetization measurements in fields up to ∠60 kOe applied parallel to each of the principal axes. In the 〈100〉 case, the transition from the A toan intermediate ferrimagnetic (Q) state is first‐order at 4.2 K (critical field Hc?21 kOe) but is continuous from ∠6 K up to TN, as Hc→O. The Q‐to‐paramagnetic (P) transition is rapid but continuous at 4.2 K (Hc?40 kOe) and becomes broad as TN is approached. In the 〈110〉 case the A‐to‐Q transition remains essentially first‐order from 4.2 K (Hc?15 kOe) up to TN; above TN rapid P‐to‐Q transitions occur at very high fields. The magnetic structure of the Q state is found to be that of HoP.

The magnetic excitation spectrum in a paramagnetic singlet‐doublet system is calculated using a diagrammatic high density expansion technique. The lowest order diagrams, which correspond to the random phase approximation (RPA), give a detailed description of the wavevector and temperature dependence of the four exciton modes in Praseodymium in terms of a Hamiltonian including isotropic Heisenberg exchange interactions and anisotropic, dipolar‐like interactions. The leading contributions to the linewidths of the excitations are obtained by extending the 1/Z expansion of the generalized susceptibility propagators one order beyond the random phase approximation. This damping corresponds to spin wave scattering on single‐site fluctuations. The theoretical spectral functions are in detailed agreement with experiment.

This paper summarizes recent investigations of the magnetic excitations of the spin density wave (SDW) in pure Cr in both the low temperature longitudinally polarized phase (T < 122K) and in the higher temperature transversely polarized phase (122K < T < 312K). In both phases spin wave modes of very high velocity are observed originating from the incommensurate Bragg points. In the transversely polarized SDW phase new additional excitations are observed, centered in reciprocal space at the (1,0,0) commensurate point. These excitations are not affected by a magnetic field. Inelastic scattering in the paramagnetic phase above the Neel point (312K) is observed in a reasonably well localized region of reciprocal space near (1,0,0) indicating that there are spin-spin correlations extending over many bcc unit cells and persisting to temperatures at least as high as 1.7 T/sub N/.

Achieving suitable magnetic properties in ceramic ferrites through thermomechanical treatments rather than through varying the processing and fabrication parameters alone are investigated. The high temperature phase transformation in lithium ferrite (LiFe5O8) spinel and the defects in LiFe5O8 and NiFe2O4 are studied using high voltage transmission electron microscopy in an effort to characterize the microstructures. Results show that a dispersion of paramagnetic LiFeO2 particles in LiFe5O8 matrix gives rise to increased squareness of the hysteresis curve and increased coercivity. Annealing treatments of sintered ferrites remove undesirable intra‐granular {100}1/4〈110〉 cation stacking faults and improve hysteresis loop parameters.

For Fe3−xSnxO4 at 300 K and x≳0.1, a paramagnetic quadrupole doublet pattern, in addition to the usual two magnetic patterns, is observed in the 57Fe NGR spectra. This doublet is due to A site Fe2+ whose concentration for 0.1?x?0.5 is such that approximately equal amounts of Fe2+ and Fe3+ are on the B site. The 200 kG field at the Sn4+ site at 300 K is smaller than that in NiFe2O4. At 80 K a paramagnetic quadrupole doublet is observed in the 119Sn NGR spectrum and is due to Sn2+.

A detailed electron paramagnetic resonance investigation of hexagonal, polycrystalline Mg‐Mn alloys with Mn concentrations of 0.49, 0.11, and 0.02 atomic per cent has been made at 9.4 and 23.5 GHz and at temperatures as low as 2.1 K. The results are similar to those obtained in cubic Cu‐Mn alloys. In the paramagnetic state the data are well explained by the relaxation bottleneck theory of Hasegawa. The spin‐orbit induced spin‐flip relaxation rate of the conduction electrons via the Mn ion cores is 17 ± 4 × 1010 sec−1 (at. % Mn)−1; and the smallest value of ∣Jsd∣ consistent with the observed relaxation bottleneck is 0.12 eV. A transition to antiferromagnetic resonance was observed at 9 ± 1, 5 ± 1, and 2 3/4 ± 1/2 K for Mn concentrations of 0.49, 0.11, and 0.02 at. %, respectively. In the AFM state the resonance shifted rapidly downfield and the linewidths increased slightly as the temperature was lowered, but the observed dependence of the shift on frequency was less than the expected inverse dependence.