Abstract: Effects of intra-state correlation on the variable range hopping are investigated in the absence and presence of a magnetic field. In the absence of a magnetic field, Mott's expression for the resistivity, ρ∝exp [ T 0 / T ] 1/4 , still holds in its temperature dependence. However, the prefactor T 0 now depends on two types of localization lengths brought about by the intra-state correlation. Magnetoresistance is found to be positive due to the intra-state correlation. It shows a linear dependence on a magnetic field in lower magnetic fields and saturates above a certain magnetic field.

Abstract: The magnetic structure of a weak ferromagnetic Mn 3 Sn has been studied by polarized neutron diffraction at room temperature. Large flipping ratios were observed for the 100 and 110 reflections under application of a magnetic field in the c -plane perpendicular to the scattering vector. The spin structure deduced from the h 0 l and h h l reflections has a triangular configuration but the spin plane is not determined. For applied field parallel to [010] the spin-A is parallel to [010], but for applied field parallel to [\bar110] the spin-B is antiparallel to [\bar110]. The magnetic form factor of the Mn atom agrees with the calculated Mn 2+ form factor and the magnetic moment is 1.78 µ B /Mn.

Abstract: The article by Villain [Z. Phys. B — Condensed Matter33, 31 (1979)] is discussed and a modified magnetic phase diagram is suggested for the spinel system (AB2O4) in which theA andB sites are partially (or completely) occupied by magnetic atoms. This diagram takes into account the antiferromagnetic exchange interactionsJAA,JBB andJAB between nearest neighbor cations of various types. Regions of paramagnetic, antiferromagnetic, ferrimagnetic and possible spin glass behaviour are indicated on the diagram.

Abstract: The magnetic properties of microcrystals are discussed on the basis of results obtained by use of M?ssbauer spectroscopy. Spectra of microcrystals with dimensions smaller than about 100 A are influenced by magnetic fluctuation effects such as superparamagnetic relaxation and collective magnetic excitations, and these effects allow a determination of the product of the particle size and the magnetic anisotropy energy constant. Measurements on ferromagnetic and ferrimagnetic particles as a function of applied magnetic fields allow a determination of the particle volume. The anisotropy energy constants of microcrystals of Fe, Co, Ni and Fe3O4 are found to change upon chemisorption. Spectra of small particles at low temperatures also give information on the magnetic properties of the atoms in the surface layer. These studies as well as thin film studies show that no magnetically dead layers are present at the surface of the samples. In the case of metallic iron an enhanced magnetic hyperfine field is found, in agreement with theoretical results.

Abstract: The disclosure is directed to a wheel-type magnetic refrigerator capable of cooling over a large temperature range. Ferromagnetic or paramagnetic porous materials are layered circumferentially according to their Curie temperature. The innermost layer has the lowest Curie temperature and the outermost layer has the highest Curie temperature. The wheel is rotated through a magnetic field perpendicular to the axis of the wheel and parallel to its direction of rotation. A fluid is pumped through portions of the layers using inner and outer manifolds to achieve refrigeration of a thermal load.

Abstract: A model previously used for treating thermodynamic properties is developed further to discuss the wave-vector-dependent susceptibility chi (q) and the associated static correlation functions. A consistent theory is given of the temperature dependence of the uniform susceptibility and of the wave-vector and temperature dependence of paramagnetic diffuse neutron scattering. The theory is applied quantitatively to CeFe2, Fe and MnSi above their magnetic ordering temperatures and to FeSi at high temperatures. In CeFe2 and MnSi the enhancement of the Curie constant and the forward scattering peak in the neutron data are both attributed to long-wavelength 'longitudinal' fluctuations of the magnetic moment superposed on strong transverse spin disorder. The situation is predicted to be similar in BCC Fe and this differs sharply from the strong short-range order picture of Prange and Korenman (1978), Capellmann (1979) and Sokoloff (1975).

Abstract: EPR and electrical conductivity measurements under controlled thermal cycles demonstrate that a phase transition is occurring at about 22 K in (TMTSF)2ClO4. Slow cooling (12 K/h) yields a stable ground state exhibiting Pauli paramagnetism above and superconductivity below 1.2 K. In contrast, fast cooling (30 K/min.) yields a metastable magnetic (SDW) state below 4 K as indicated by increasing resistivity and disappearance of the EPR signal with decreasing temperature.

Abstract: We have subjected thermally grown films of SiO2 on Si substrates to Co60 gamma irradiation. Using electron spin resonance we observe three radiation-induced paramagnetic defect centers in the structures at room temperature. One resonance appears to be unambiguously associated with trivalent silicon bonded to three other silicons at the Si/SiO2 interface. Two other resonances are very much like resonances observed earlier in irradiated high purity bulk SiO2; those bulk SiO2 resonances have been associated with trivalent silicons bonded to three oxygens and unpaired electrons in nonbonding oxygen 2p orbitals.

Abstract: A powder neutron diffraction study and subsequent line-profile analysis of the magnetic structure of iron(III) molybdate at 2 K indicate that it is a four-sublattice antiferromagnet containing four crystallographically distinct iron atoms in the space group P2/sub 1//a (b unique). An analysis of covalency in iron(III) molybdate reveals a higher degree of covalency (A/sub sigma//sup 2/ + 2A/sub ..pi..//sup 2/ + A/sub s//sup 2/ = 9.15%) in the iron(III) to oxygen bonds than is found in the structurally related iron(III) sulfate (6.1%). A Moessbauer-effect study indicates that, at 11.8 K and above, iron(III) molybdate is paramagnetic with parameters typical of an octahedral high-spin iron(III) compound. Between 11.72 and 11.59 K both ordered and paramagnetic phases coexist. Below 11.72 K the Moessbauer spectrum shows the presence of spontaneous magnetic ordering with four inequivalent magnetic hyperfine fields. On three of the iron sites, the hyperfine fields are rather similar while the fourth site exhibits a significantly greater hyperfine field. The differences between various combinations of the four hyperfine fields show maxima at about 10 K. At 1.14 K the field values are 540, 529, 519, and 509 kOe. The isomer shifts for each site are similar at ca. 0.52 mm/s, and themore » quadrupole shifts are small at ca. +- 0.01 mm/s. Magnetic susceptibility studies confirm that the material is paramagnetic above ca. 20 K, with an effective magnetic moment of 5.92 ..mu../sub B/ and a Curie-Weiss temperature of -55.6 K. The magnetic susceptibility shows a peak of ca. 10 K, the magnitude of which increases with decreasing applied field between 45.81 and 9.95 kG. 8 figures, 2 tables.« less

Abstract: The pattern of the electron currents, induced in the benzene molecule by uniform magnetic fields, has been visualized by plotting modulus and direction of the quantum mechanical current density vector evaluated within the coupled Hartree–Fock approximation assuming a basis set of 198 CGTOs. The electron motion is characterized by axial and toroidal vortices and the paramagnetic σ circulation overcomes the diamagnetic π ring current. Intense localized circulations occur about carbon nuclei and carbon–carbon bonds, which give rise to important deshielding effects upon protons. The delocalized currents are most intense in the environment of carbons; delocalized currents are also present, and no actual ’’superconductivity’’ of π electrons can be accounted for. The reported results document that London’s ring current is a rough oversimplification, affected by some unnecessary and unphysical hypotheses.

Abstract: We report measurements of the ac magnetic susceptibility and dc resistive superconducting transitions in the organic superconductor (TMTSF)2C104. Inductive measurements show complete diamagnetic shielding below a broad transition and initial flux penetration at very low fields [Hc1(0) < 1 Oe]. The resistive transition is also broad, but occurs at a significantly higher temperature than the inductive transition, Tc = 1.0 K and 0.65 K respectively. Resistance measurements also show evidence of a phase transition in the vicinity of 24 K. Magnetic field induced transitions, measured both inductively and resistively, show marked anistropy both in magnitude and in breadth of the transition. Results suggest that (TMTSF)2C104 is a quasi ID or 2D superconductor at high temperatures and high magnetic fields and an anisotropic bulk superconductor at low temperatures and fields. Associated thermoelectric power measurements suggest that spin density waves coexist with the superconducting state.

Abstract: For 3d metals the atomic moments derived from Curie‐Weiss susceptibility are often significantly larger than the value obtained in the ferromagnetic state from the saturation magnetization Indeed the Heisenberg model is known to be inappropriate for metallic systems which in general are better described by band theory The ground state properties of metallic magnets, particularly the occurrence of nonintegral moments, are well accounted for using the Stoner theory, but the model is less satisfactory at elevated temperatures The persistence of spin waves above TC and the observation of paramagnetic moments indicate that the 3d band remains split in the paramagnetic phase in contradiction with mean field theory A direct way of establishing the existence of paramagnetic moments is by the paramagnetic scattering of neutrons The technique is particularly enhanced if polarization analysis is employed to obtain a unique estimate of the magnetic cross section In the present paper, we report the results of re

Abstract: Alloys of II–VI semiconductors with magnetic semiconductors like MnS, MnSe, MnTe—the diluted magnetic semiconductors—occur in a homogeneous phase with the zinc blende or wurzite structure, over a large composition range. Thanks to the presence of the substitutional Mn++ and in turn, a strong Mn++–Mn++ and Mn++–band electron exchange interaction, these alloys exhibit striking magnetic properties. Raman scattering is a powerful technique for their investigation. This is illustrated with results on Cd1−xMnxTe which exhibits (1) Raman lines associated with ΔmS=±1 as well as ΔmS=±2 paramagnetic transitions within the Zeeman multiplet of the S=5/2 ground state of Mn++ (2) the paramagnetic transitions in combination with LO‐phonons (3) spin‐flip transition of a bound electron (4) evolution of the paramagnetic line of Mn++ into the high frequency component of the magnon line split into a doublet by the magnetic field. The magnon line has been studied as a function of temperature, composition, and magnetic field.

Abstract: The magnetic behaviour of a basalt glass and glass-ceramic was studied by magnetization measurements between 4 and 800 K as a function of a wide range of magnetic fields (H) between 0 and 60 kG. For the as-annealed glass it was found that nearly all the iron ions behaved as paramagnetic ions. In the samples heat-treated at 700 and 900°C, the magnetization (M) values showed three magnetic components: paramagnetic Fe2+ ions, magnetite in a superparamagnetic and in a ferrimagnetic state. This confirmed our previous Mossbauer results. The superparamagnetic behaviour of the fine particles of magnetite was interpreted by Langevin's theory. From the M (H) and M(T) values we evaluated the percentage of each component as a function of temperature, the magnetization values in the saturated states, the mean particle diameter and the particle size distributions.

Abstract: The magnetic behavior of hcp‐Fe (epsilon iron) has been investigated by the Mossbauer Effect over a wide range of temperature T, pressure P, and applied magnetic field H0. The internal field Hi of the induced moment is given by Hi=0.20±0.01 H0 and is independent of T and P. Enhanced paramagnetism is suggested as the most likely origin for a contribution of this magnitude to Hi.

Abstract: Mossbauer spectroscopy of nitrided and carbonitrided iron powders and plates with total interstitial atom contents of between 24 and 33 at% has allowed the variation with composition of the hyperfine magnetic fields of metal atoms with 2 or 3 close interstitial atoms to be determined. Fe atoms with three non-metal nearest neighbours and paramagnetic behaviour have also been detected. Only when the content of non-metal atoms goes beyond 30 at%, do Fe atoms in e-carbonitrides display higher magnetic fields than in the corresponding e-nitrides. The lower number of electrons contributed to the iron 3d-orbitals by C atoms than by N atoms is considered the cause of the above phenomenon. The variation of other hyperfine parameters with composition is also discussed.