Abstract: We report the inducement of a ferromagnetic order by photogenerated carriers in a novel III-V--based magnetic semiconductor heterostructure $p$-(In,Mn)As/GaSb grown by molecular beam epitaxy. At low temperatures $(l35\mathrm{K})$, samples preserve ferromagnetic order even after the light is switched off, whereas they recover their original paramagnetic condition above 35 K. The results are explained in terms of hole transfer from GaSb to InMnAs in the heterostructure, which enhances a ferromagnetic spin exchange among Mn ions in the InMnAs layer.

Abstract: A zero bias anomaly is observed at low temperatures in the current-voltage characteristics of ferromagnetic tunnel junctions; the drop in the junction resistance with increasing bias voltage is greater for antiparallel alignment of the magnetic moments of the magnetic electrodes than for parallel alignment. The resulting decrease in the magnetoresistance of the junction is accounted for by spin excitations localized at the interfaces between the magnetic electrodes and the tunnel barrier.

Abstract: For large paramagnetic molecules in solution, the paramagnetic and diamagnetic contributions to the magnetic susceptibility are comparable and may be determined by NMR (Evans' method) in the same conditions (concentration, temperature, solvent). Theoretical considerations show that the solvent correction similarly affects both measurements and cancels in the combined equations calculating the magnetic susceptibilities and the magnetic moments. These simplified equations have been successfully applied for the determination of the magnetism of self-assembled heterodinuclear 3d-4f supramolecular complexes in acetonitrile.

Abstract: Photosynthesis produces the oxygen necessary for all aerobic life. During this process, the manganese-containing oxygen evolving complex (OEC) in photosystem II (PSII), cycles through five oxidation states, S0−S4. One of these, S2, is known to be paramagnetic and gives rise to electron paramagnetic resonance (EPR) signals used to probe the catalytic structure and function of the OEC. The S0 state has long been thought to be paramagnetic. We report here a Mn EPR signal from the previously EPR invisible S0 state. The new signal oscillates with a period of four, indicating that it originates from fully active PSII centers. Although similar to the S2 state multiline signal, the new signal is wider (2200 gauss compared with 1850 gauss in samples produced by flashing), with different peak intensity and separation (82 gauss compared with 89 gauss). These characteristics are consistent with the S0 state EPR signal arising from a coupled MnII−MnIII intermediate. The new signal is more stable than the S2 state sign...

Abstract: The title compounds (R = La, Pr, Nd, Sm, Eu, Tb, Ho, Er) have been prepared in polycrystalline form by a citrate technique and, excepting the Sm and Eu phases, structurally studied by high-resolution neutron powder diffraction. All the materials are isostructural (space group Pbam, Z = 4) and contain infinite chains of octahedra sharing edges, linked together by and units. The size of the three kinds of coordination polyhedron regularly decreases as R cations become smaller. A bond-valence study allowed us to detect the presence of important tensile and compressive stresses in the crystal structure of , which are progressively released along the series as the rare-earth size decreases. The magnetic properties strongly depend on the nature of R, going from the spin-glass behaviour observed at low temperature in to the field-induced transitions exhibited by . A cusp in the susceptibility curves suggests an antiferromagnetic ordering at low temperatures, which is masked in the compounds containing strongly paramagnetic rare earths (Tb, Ho, Er). At high temperatures the paramagnetic moments are consistent in all cases with the presence of high-spin and cations.

Abstract: “Diffusion-diffraction” experiments on water, yielding “q-space” plots, were conducted on suspensions of oxygenated (diamagnetic) human erythrocytes. (i) These suspensions displayed diffusion-diffraction of water; (ii) the shape of the q-space plots depended on the direction along which the diffusion was measured, thus implying alignment of the cells in the magnetic field of the NMR spectrometer; (iii) the diffusion anisotropy was altered in a predictable way by converting the hemoglobin to a paramagnetic form; (iv) the shapes of the q-space plots were altered in a predictable way by inhibiting water transport; (v) the pseudo-first order rate constant characterizing the covalent inhibition of water transport, by p-chloromercuribenzenesulfonate (p-CMBS), was measured; and (vi) the cell diameter and intercellular spacing were measured from the positions of the interference minima and maxima in the q-space plots. The relevance of these findings to NMR-based histological characterization of tissues, and the implications, for magnetic resonance imaging (MRI), of eryth-rocyte alignment in the small vessels of the brain in particular, are noted.

Abstract: SUMMARY The measurement of the temperature variation of magnetic susceptibility can be used for the separation of ferromagnetic and paramagnetic susceptibility components. The method suggested by Hrouda (1994) assumes a hyperbolic dependence of paramagnetic, susceptibility and constant ferromagnetic susceptibility in the temperature interval used for the separation. Our new method works with a paramagnetic hyperbola again, but assumes that the ferromagnetic susceptibility temperature variation is represented by a linear relationship in the resolution interval, as indicated by the investigation of monomineralic ferromagnetic fractions.

Abstract: We present a theory of nuclear-spin relaxation appropriate to the case of a mobile liquid dipolar spin diffusing in a quasi-two-dimensional model porous system in the presence of rare paramagnetic impurities fixed at the surface of the pores. This theory predicts that the ${}^{1}\mathrm{H}$ spin-lattice relaxation rate will be linear in two parts when plotted as a function of the logarithm of the magnetic-field strength and the slopes of these distinct linear regions should be in the ratio 10:3. The theory predicts also a typical pore size dependence for such a rate. The theory is tested at several temperatures using acetone, acetonitrile, dimethylformamide, and dimethylsulfoxide on microporous chromatographic glass beads that have paramagnetic ion impurities at the level of 40 ppm. ${}^{1}\mathrm{H}$ spin-lattice relaxation rates are recorded over magnetic-field strengths corresponding to ${}^{1}\mathrm{H}$ Larmor frequencies between 0.01 and 30 MHz using a field-switched magnetic relaxation dispersion spectrometer. The data support the theory quantitatively. The diffusion constant ${D}_{I\ensuremath{\perp}}$ for the proton-bearing molecule perpendicular to the normal of the pore surface is found to be nearly a factor of 10 smaller than in the bulk solvents. It is characterized by a small activation energy similar to those in the bulk solvent. These results demonstrate that magnetic relaxation dispersion at low magnetic-field strengths in high-surface-area heterogeneous systems may be quantitatively understood in terms of the parameters of the spatial confinement and the local translational dynamics.

Abstract: Magnetic entropy change of La0.75Ca0.25MnO3 with different particle size has been investigated. Magnetic entropy change ∼4.7 J/kg K larger than that of Gd has been observed at 224 K under a magnetic field of 1.5 T in comparatively big particles. This phenomenon of large magnetic entropy change indicates that the perovskite-type manganese oxides have potential applications for magnetic refrigerants in high temperature.

Abstract: The recently reported interesting behavior of the EPR spin intensity as freshly prepared CuZSM-5 is dehydrated has been confirmed, and the interpretation offered in explanation has been tested by extending the data. Magnetic susceptibility and optical diffuse reflection spectroscopy have been used to show that the anomalous EPR data correspond to changes in symmetry rather than disproportionation of [CuOH]+ into Cu+ and Cu2+O- as H2O is removed, as previously suggested. Moreover, the relatively small negative Weiss constants suggest that antiferromagnetic coupling through the supposedly EPR silent conventional bridge species, [Cu2+−O2-−Cu2+]2+, cannot be responsible for the relatively large changes in observed EPR spin intensity on dehydration. EPR measures selectively individual paramagnetic species and ignores those of low symmetry, while magnetic susceptibility integrates over all magnetic species in the sample. The changes in the EPR intensities were much larger than those observed by magnetic suscept...

Abstract: A new approach for designing optically switchable molecular communication devices based on spin-exchange interactions is proposed in the present paper. The device is constituted from two parts, i.e., a paramagnetic block (PMB) and a coupling control block (CCB). As a prototype of this model, nickel nitroprusside, Ni[Fe(CN)5NO]·5.3H2O was synthesized, in which the nickel ion acts as the PMB and the nitroprusside molecule does as the CCB. In this compound, as there is no spin on Fe, the magnetic interaction between the neighboring Ni cations is very weak. No magnetic phase transition can be observed until 1.8 K. Photoirradiation at 475 nm causes a charge transfer from the metal, Fe, to the ligand, NO, which induces two antiferromagnetically coupled spins on Fe and NO. Furthermore, the new spin on Fe interacts ferromagnetically with those on neighboring nickels. As a result, the spins on the Ni ions, which surround the Fe with spin, form a magnetic cluster with S = 5.

Abstract: A nonhomogeneous magnetic field is generated electrochemically in an electrodeposition cell which is also an interferometer. Magnetic field strength near 0.5T produce a detectable by interferometry convective slow rotation in a diamagnetic electrolyte with electroactive (Cu2+) and indifferent (Mn2+) paramagnetic ions present in an otherwise stagnant solution with the cathode over the anode (C/A). Approximate calculation of forces and flows are attempted.

Abstract: The possibility of using the relaxation properties of nuclei for solution structure determination of paramagnetic metalloproteins is critically evaluated. First of all, it is theoretically and experimentally demonstrated that magnetization recovery in non-selective inversion recovery experiments can be approximated to an exponential in both diamagnetic and paramagnetic systems. This permits the estimate of the contribution of paramagnetic relaxation when dominant or sizable. Then, it is shown that the averaging of paramagnetic relaxation rates due to cross relaxation is often tolerably small with respect to the use of paramagnetic relaxation rates as constraints for structural determination. Finally, a protocol is proposed to use such paramagnetic relaxation rates, which depend on the sixth power of the metal to resonating nucleus distance, as constraints for solution structure determination of proteins. As an example, the available solution structure of the oxidized ferredoxin from Clostridium pasteurianum has been significantly improved in resolution especially in the proximity of the metal ions by using 69 new constraints based on paramagnetic relaxation. Proteins 29:348–358, 1997. © 1997 Wiley-Liss, Inc.

Abstract: Molecular charge-transfer salts that consist of alternating layers of organic donor molecules and inorganic anions offer the opportunity of bringing together in the same crystal lattice conduction electrons localised on the donor sublattice and magnetic moments localised on the inorganic anions. A wide range of such compounds is formed by the donor molecule BEDT-TTF [bis(ethylenedithio)tetrathiafulvalene]. Some are semiconductors, others are metals while one is a superconductor, the first containing paramagnetic 3d moments. The structures, magnetic and conductivity properties of examples from each category are reviewed.

Abstract: In solution, the degree of molecular alignment with the static magnetic field is proportional to the product of the anisotropy of the molecular magnetic susceptibility and the square of the magnetic field strength. As a result, the observed chemical shifts vary with the strength of the magnetic field and depend on the orientation of the chemical shift tensors relative to the molecule's magnetic susceptibility tensor. For protein backbone amide 15N nuclei in the complex between the zinc-finger DNA-binding domain of GATA-1 and a 16-bp synthetic DNA fragment, the observed field dependence of the 15N shifts correlates well with the dipolar couplings previously reported for this complex. This comparison indicates that, in the approximation of an axially symmetric 15N shift tensor, the unique axis of the 15N CSA tensor makes an angle of 13 ± 5° with the N−H bond vector, and has a magnitude of 168 ± 20 ppm. Magnetic field dependent 15N chemical shifts correlate well with the structure of the protein−DNA complex ...

Abstract: The isothermal change of the magnetic entropy of a magnetically ordered material upon application of external magnetic field can be calculated from the temperature and field dependence of the magnetization or of the specific heat. The adiabatic temperature change, i.e., the magnetocaloric effect (MCE) can be measured directly or can be calculated via different methods using the field-dependent specific heat values, or a combination of data obtained via magnetization and thermal measurements. In the present study, magnetic and thermal measurements were carried out on Gd75Y25(TC=232 K) and Gd48Y52(TC=161 K) samples, for applied fields ranging between 0 and 7 T. From both datasets, the magnetic entropy change and MCE values were calculated and compared, in order to assess the mutual reliability of the methods applied. The magnetically or thermally deduced specific heat discontinuities show a reasonable agreement within experimental error. Similar comparison of the calculated magnetic entropy changes reveals ...

Abstract: We have measured under pressure Mossbauer spectra of FeS and 3c-type up to 16 GPa and x-ray diffraction patterns of up to 11 GPa at room temperature. It is found for that the compressibilities of the lattice parameters exhibit definite anomalies at around 4.5 GPa and that there is no change in the crystal structure up to 11 GPa. Magnetically ordered Mossbauer spectra are observed below 6.5 GPa for FeS and 4.5 GPa for , whereas the spectra above these pressures are typical of a paramagnetic ordering with a quadrupole splitting. A large reduction in the centre shift is observed at these pressures. It is found that there is a distinct steplike feature of the magnetic hyperfine field at 3.5 GPa for FeS. The electronic states of FeS and are deduced from the volume dependences of the centre shift and the magnetic hyperfine field. Below 3.5 GPa for FeS, the electronic state has an insulating character and the electrons on the iron are well localized and thus contribute to the magnetic moment. In the intermediate-pressure range, from 3.5 to 6.5 GPa for FeS and below 4.5 GPa for , the electronic state is like a semimetallic one. Above 6.5 GPa for FeS and 4.5 GPa for , the electronic bandwidth is large enough to cause the state to become metallic and produces a collapse of the iron magnetic moment.