Abstract: Magnetic susceptibilities of single-crystal $\ensuremath{\gamma}\ensuremath{-}{\mathrm{O}}_{2}$ and preferentially oriented polycrystalline samples of $\ensuremath{\beta}\ensuremath{-}{\mathrm{O}}_{2}$ and $\ensuremath{\alpha}\ensuremath{-}{\mathrm{O}}_{2}$ have been measured, employing a mutual-inductance bridge method. The susceptibility of paramagnetic $\ensuremath{\gamma}\ensuremath{-}{\mathrm{O}}_{2}$ is isotropic and exhibits a temperature dependence which is not strictly Curie-Weiss, due to short-range correlations and partially hindered rotation. The susceptibility of $\ensuremath{\beta}\ensuremath{-}{\mathrm{O}}_{2}$ exhibits very little anisotropy, but has an unusual temperature dependence which is probably due to the novel behavior of the lattice constants, modulation of inplane and out-of-plane exchange interactions, and short-range order. The susceptibility of anti-ferromagnetic $\ensuremath{\alpha}\ensuremath{-}{\mathrm{O}}_{2}$ is anisotropic, and data from five differently oriented samples have been analyzed in terms of principal antiferromagnetic susceptibilities. The data are consistent with the assumption that the easy axis is the twofold axis, ${\stackrel{\ensuremath{\rightarrow}}{\mathrm{b}}}_{\ensuremath{\alpha}}$, though the direction ${\stackrel{\ensuremath{\rightarrow}}{\mathrm{a}}}_{\ensuremath{\alpha}}$ cannot be excluded. A comprehensive analysis of the present susceptibility results and other magnetic, spectroscopic, and thermal measurements is made, with special reference to $\ensuremath{\alpha}\ensuremath{-}{\mathrm{O}}_{2}$. The perpendicular susceptibility implies an unreasonably large N\'eel temperature, 211 K, and a correspondingly large intersublattice exchange interaction, $\frac{|{J}_{2}|}{k}=19.8$ K. The effects of anisotropy and zeropoint spin deviations do not reduce this estimate by more than 15%. The temperature dependence of the parallel susceptibility suggests a much smaller value for the effective exchange interaction, $\frac{|J|}{k}=5.3$ K, and appears to be well accounted for assuming a single spin-wave excitation. Antiferromagnetic resonance frequencies are analyzed and shown to yield, on assuming a dominant anisotropy equal to that of the free molecule, $\frac{|{J}_{2}|}{k}=4.3$ K. An approximate separation of lattice and magnetic heat capacities is effected, and a value $\frac{|J|}{k}=3.0$ K deduced. The data appear to require the assumption of two spin-wave modes. Except for the perpendicular susceptibility, experimental results suggest a N\'eel temperature between 30 and 40 K. Meanfield and other theories lead to similar estimates, assuming that $\frac{|J|}{k}$ is between 3 and 4 K. The effect of the anisotropy on ${T}_{N}$ is minor, and no significant spin-shortening effect is predicted. Other experimental results are considered, and a disparate set of estimates for the exchange interaction and zone-boundary spin-wave energies is discussed. Including the effects of intrasublattice exchange interactions within the context of a two-sublattice model does not seem sufficient to remove the various discrepancies. An approximate calculation of relative overlap integrals and exchange interactions between different pairs of molecules in $\ensuremath{\alpha}\ensuremath{-}{\mathrm{O}}_{2}$ is made. It is suggested that a multisublattice model for the magnetic structure, and possibly one involving noncollinear sublattices, may provide an eventual resolution of the various difficulties. A "quasi-two-dimensional" description of $\ensuremath{\alpha}\ensuremath{-}{\mathrm{O}}_{2}$ is also considered, but appears not to offer a satisfactory explanation of the unusual and imperfectly correlated properties of this phase.

Abstract: Neutron diffraction measurements on polycrystalline samples show that UPd2Si2, UPd2Ge2 and URh2Si2 become antiferromagnetic below temperatures of 150K, 140K and 137K respectively. The magnetic moment ordering in UPd2Si2 and UPd2Ge2 is represented by a static longitudinal wave propagating along the c axis of the tetragonal body-centred crystal lattice. The magnetisation wave is polarised in the direction of the c axis: q=(0, 0, 0.662+or-0.010)c* in UPd2Si2 and q=(0, 0, 0.748+or-0.010)c* in UPd2Ge2. At 40K, UPd2Si2 exhibits a magnetic phase transition: a commensurate magnetisation wave with q=(0, 0, 1)c* represents the growth of a simple antiferromagnetic ordering. URh2Si2 is a collinear antiferromagnet with coinciding magnetic and chemical unit cells. The sequence of ferromagnetic sheets piled up along the tetragonal axis is given by +-. The values of the root mean square of the magnetic moment on the U ion at 4.2K are found to be 1.96 mu B, 1.97 mu B and 1.96 mu B for UPd2Si2, UPd2Ge2 and URh2Si2 respectively. The observed magnetic ordering schemes are discussed in terms of the RKKY exchange interaction. Neutron diffraction measurements performed at zero magnetic field show that URh2Ge2 is paramagnetic at 4.2K.

Abstract: 2014 A review is given of electron paramagnetic resonance (EPR) research of substitutional defects in ABO3 double oxides crystallizing in the perovskite structure. In section 2, the valency and lattice sites are considered. In section 3, the existence of transition metal-oxygen vacancy pairs, Me-Vo, is reviewed, and in 4, their atomic structure is analysed. In section 5, the determination of the local position of Fe3+ at B sites in crystals undergoing ferroelectric phase transitions is presented, and its anomalously low cubic splitting EPR parameter discussed in 6. J. Physique 42 (1981) 551-557 AVRIL 1981,

Abstract: A self-consistent linear-combination-of-Gaussian-orbitals band-structure calculation for paramagnetic chromium employing a local exchange approximation has been performed. The density of states, Fermi surface, and x-ray form factors have been obtained and compared with available experimental data. New interpretations of some of the neutron scattering data are made, with good agreement in general for all the data. The Compton profiles and the optical conductivity have also been obtained using the full matrix element $\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}}$ dependence in Brillouin-zone integrations. Comparison with experiment is made for both, and correlation with experiment is good if appropriate angular averages or lifetime effects are included.

Abstract: Neutron scattering measurements on pure chromium metal have been performed under various conditions of experimental resolution, energy transfer, temperature, and magnetic field. The temperature and energy dependence of the commensurate-diffuse scattering surrounding the (0,0,1) point in reciprocal space has been followed from the spin-flip temperature (${T}_{\mathrm{sf}}$=122 K) to temperatures as high as 700 K, well above the N\'eel point (${T}_{N}$=312 K). Magnetic correlations extending over 11 bcc unit cells persist to these high temperatures. The spectral width of the magnetic scattering is found to increase rapidly with temperature above ${T}_{N}$. The importance of the commensurate-diffuse modes of excitation in the disappearance of the long-range-ordered spin-density-wave (SDW) state at ${T}_{N}$ is discussed. The magnetic field dependence of the excitations in the transversely polarized SDW phase has been investigated and found to be absent. Evidence is also presented for the absence of a spin-wave energy gap greater than 50 \ensuremath{\mu}eV. We have placed the scattering in the paramagnetic phase on an absolute scale by normalizing to the integrated intensities of selected phonons, and have estimated an effective magnetic moment per atom.

Abstract: 2014 A method has been developed for determining the structure of the water/surfactant interface and the configuration of the surfactant molecules in micelles. In this method, NMR is used to measure the magnetic dipolar interactions between the nuclei of the surfactant molecules and paramagnetic counterions adsorbed on the surface of the micelles. The experiment compares the relaxation rates of nuclei belonging to different chemical groups in the surfactant molecules; in some simple cases these relaxation rates only depend on the distances between the nuclei and the ions. Then the measured relaxation rates can be related to the populations of the nuclei in layers located at various depths from the paramagnetic surface. According to the data, the structure of these successive layers in a spherical micelle can be discussed in the following terms : (i) outermost layers containing the hydrated charges (how smooth or regular are they ?) ; (ii) layers of water/hydrocarbon contact (how deep does water penetrate in the micelle ?) ; (iii) layers of the hydrocarbon core (how disorganized is the packing of the surfactant chains ?). J. Physique 42 (1981) 847-859 JUIN 1981,

Abstract: The hydrides of ZrMn/sub 2+x/, with x = 0.6, 0.8, and 1.8, have been prepared and studied. Hydrogen vapor pressure rises rapidly as x increases, increasing more than 50-fold for ZrMn/sub 3/ /sub 8/-H compared to the ZrMn/sub 2/-H system. Capacity of the systems for hydrogen is large; the hydrogen densities relative to that of liquid hydrogen range from 0.95 to 1.48. Kinetics of exchange of hydrogen between the hydride and gaseous hydrogen is very rapid; uptake of hydrogen is 90% complete within 1 min. This appears to be a consequence of the thinness of the oxide coating and the high concentration of Mn in the surface, as determined by Auger spectroscopy. Magnetic measurements show that hydrogenation transforms the paramagnetic host metal into a ferromagnetic material. The ordered moments range from 0.04 to 0.18 ..mu beta.. er formula unit of (Zr, Mn)Mn/sub 2/-H, increasing wth increase in the stoichiometric excess of Mn. The ordered moments are ascribed to this excess Mn and are approx. 0.5 ..mu beta../(Mn atom). The system seems to consist of regions in which ferromagnetic interactions prevail interspersed with those in which antiferromagnetic interactions predominate. ..delta..H and ..delta..S for the evolution of hydrogen are unusually small formore » systems of this nature. This is presumably a consequence of the strong influence of hydrogen on the magnetic nature of the system. The low values of ..delta..H are very significant in regard to practical applications of these materials for hydrogen storage.« less

Abstract: The magnetic properties of the (001) surface of chromium at finite temperature are investigated by means of spin-fluctuation theory. It is found that, in contrast with the behavior in the bulk, large localized magnetic moments form at the surface. Interactions between these moments and their coupling to bulk spin fluctuations are included in the calculations. The results show that magnetic ordering at the surface persists well above the bulk N\'eel temperature. Comparison is made with available experimental results.

Abstract: The magnetizations and Curie temperatures of amorphous particles produced by spark erosion are found to be greatly reduced from the values for amorphous ribbons of the same compositions. The differences increase as particle size decreases. This behavior is interpreted as a decrease of chemical short-range order in the particles as a result of their faster quenching rate. Anomalous low-field behavior in the critical region also supports this conclusion.

Abstract: Several kinds of Fe-base amorphous alloys with transition metals were prepared by means of a co-sputtering technique. The reduction of the magnetic moment of Fe-Ta and Fe-Nb amorphous alloys is much more pronounced than that of Fe-Hf and Fe-Zr amorphous alloys. Fe-Mo, Fe-V and Fe-W amorphous alloys are paramagnetic. The concentration dependence of the Curie temperature also exhibits a similar tendency. Such behavior can be explained by a d-band filling model. The magnetic-carrier ratio is larger than unity, indicating itinerant magnetic behavior. The reduced magnetization curves of the present alloys are flatter than those of crystalline Ni and Fe, and Co-base amorphous alloys.

Abstract: The nematic-isotropic transition temperature was measured by means of an optical technique as a function of applied magnetic field for the material octyl-cyanobiphenyl. The results represent the first unambiguous demonstration of the magnetic field term in the thermodynamic equation for a liquid-crystal phase transition.

Abstract: Magnetic properties of the implanted layer in thin garnet films can be obtained from ferromagnetic resonance experiments. Approximate profiles of implantation induced anisotropy can be obtained using perpendicular resonance alone. For maximum information and accuracy, both perpendicular and parallel resonance spectra are needed, and measurements should be made on a number of samples from which varying amounts of the implanted layer have been removed by ion milling. For narrow linewidth materials it is possible to deduce profiles of H k , 4πM, and A and to determine the value of g in the implanted layer. Methods are presented for the accurate calculation of parallel ferromagnetic resonance (FMR) spectra with depth varying magnetic parameters. This method of analysis has been successfully applied to a yttrium iron garnet (YIG) film substituted with Gd, Tm, Ga, and implanted with He ions at 140 keV with a density of 3 × 1015cm-2.

Abstract: Research on the phosphorescent states of organic molecules has experienced a very active and rapid growth since World War II. The growth was undoubtedly initiated in 1944 by the identification of phosphorescence in organic molecules with the triplet state by Lewis and Kasha [1]. Since then, a great number of experimental and theoretical studies on the triplet state have been accumulated [2], probably because of the recognition of the key role of the triplet state in photochemistry, photophysics, and photobiology. The paramagnetism due to two parallel spins characteristic of the triplet state has also attracted many researchers in the field of magnetic resonance.

Abstract: Below 230 K CeFe2 orders with a saturation magnetic moment of 1.15 μB/Fe at 4.2 K. The paramagnetic effective moment deduced from the Curie‐Weiss law is 3.7 μB. Reported here are the results of neutron paramagnetic scattering measurements obtained between 300 K and 870 K on CeFe2. The technique of polarization analysis has been used to obtain a unique measurement of the magnetic cross‐section. The Fe moment determined in this way is about 1 μB, close to that observed in the ferromagnetic state. However, strong ferromagnetic correlations are found to persist up to the highest temperature used in this study, i.e., 870 K. The results are in complete agreement with recent theories which tend to reconcile 3d band magnetism with the persistence of a moment in the paramagnetic state. In conclusion, effective moments derived from susceptibility measurements do not allow an understanding of the 3d magnetism in the paramagnetic state.

Abstract: The effect of structure on the magnetic properties of amorphous alloys is discussed, with emphasis on the effect of fluctuations in the local atomic structure. It is pointed out that the structural fluctuations are best described by the internal stresses of long, medium or atomic range, and some of the magnetic properties are discussed in terms of these stresses. The properties discussed include the Curie temperature, saturation magnetization, magnetostriction, spin wave stiffness, paramagnetic susceptibility, changes in the Curie temperature, induced anisotropy and magnetic after-effect. The role of the structural defects on the last three is also discussed.

Abstract: The electrical conductivity of Li-Ni ferrites was studied as a function of composition and of temperature. X-ray analysis and Seebeck coefficient studies were also carried out so that the conductivity of these mixed ferrites could be discussed. The dependence of the electrical conductivity of Li-Ni ferrites on composition is explained on the basis of the cation distribution. All the ferrites exhibit a transition near the Curie temperature with a change in slope of the conductivity (log(σT)) versus temperature (103T) curve. It is found that the activation energy in the paramagnetic region is higher than that in the ferrimagnetic region for all the ferrites.