Search

Mossbauer emission measurements show that the isolated 57 Fe 3+ probe pins a Cu spin-glass cluster in superconducting La 2− x Sr x CuO 4 for x x t ( x t is roughly at the centre of the superconducting x range in the phase diagram), whereas for x > x t the probe is essentially coupled with an induced localized Cu magnetic moment.

When the Zn 2+ level is increased in YBa 2 (Cu 1− x Zn x ) 3 O 7 , we observe that the thermal variation of 1/T 1 for the S ′= 1 2 ground state of Yb 3+ probes progressively crosses over from a dependence showing gap-like features ( x = 0) to one showing gapless features ( x = 0.06 and above).

(1994). Efficacy of ivermectin treatment of Loa loa filariasis patients without microfilaraemias. Annals of Tropical Medicine & Parasitology: Vol. 88, No. 1, pp. 93-94.

Using Mossbauer spectroscopy, we have followed the internal (molecular) field produced by the short-range correlated Cu(2) moments on 170 Yb 3+ probes diluted at the Y 3+ sites in YBa 2 Cu 3 O x as a function of oxygen level and temperature. At intermediate oxygen levels two local situations coexist, attributed respectively to local magnetic (spin-glass like) and local superconducting behaviour. We monitor the oxygen dependence of the relative amounts of the two fractions.

The compound YbNiSn is studied by means of 170 Yb Mossbauer spectroscopy and single crystal magnetisation measurements. The ferromagnetic Yb 3+ magnetic moment is found to lie along the c -axis and its saturated value is 0.85 μ B . The Curie temperature is T c = 5.65 K. The results show that the exchange coupling is anisotropic and that the ferromagnetic moment is reduced by Kondo fluctuations with a Kondo temperature T 0 = 2 K.

Resume Introduction. – Les ruptures spontanees de rate sont des complications rares, potentiellement fatales de nombreuses maladies infectieuses. Le traitement classique reste la splenectomie mais plusieurs travaux recents ont souligne l’interet d’un traitement conservateur. Exegese. – Les auteurs rapportent trois cas de ruptures de rate compliquant respectivement une mononucleose infectieuse, un paludisme a P. vivax et une dengue. Les aspects diagnostiques, les moyens therapeutiques et les indications sont passes en revue, un algorithme decisionnel est propose. Il s’agissait de trois militaires âges respectivement de 23, 24 et 35 ans hospitalises pour des syndromes douloureux de l’hypochondre gauche. La tomodensitometrie abdominale a confirme une rupture partielle (hematome splenique) dans les deux premiers cas et une rupture complete avec hemoperitoine au cours de la dengue. L’abstention chirurgicale a permis la guerison dans les deux formes partielles, la splenectomie ayant ete inevitable dans le cas de dengue. Les ruptures spleniques sont inaugurales ou viennent compliquer l’evolution de l’infection. Elles surviennent spontanement ou au decours d’un traumatisme mineur pouvant etre passer inapercu. La forme typique est aigue imprevisible, mais il existe des formes progressives. Le diagnostic repose sur l’echographie et la tomodensitometrie abdominale. Le dogme de la splenectomie tend a etre remplace par une approche conservatrice medicale ou chirurgicale. Sous reserve de criteres cliniques stricts et de la possibilite d’une surveillance, l’abstention chirurgicale peut s’appliquer a des cas selectionnes. En cas d’indication chirurgicale, les techniques de preservations spleniques sont seduisantes. La splenectomie etant reservee aux formes graves et aux echecs du traitement initial. Conclusions. – Les ruptures spontanees de rate sont rares au cours des infections. Leur prise en charge est idealement medicochirurgicale. Un traitement conservateur est possible chez des patients selectionnes, sous reserve de criteres cliniques stricts et d’un suivi clinique et radiologique prolonge.

A ce jour en Polynesie Francaise et en Nouvelle-Caledonie, les patients presentant une infection ciguaterique recoivent un traitement standard: calcium+polyvitaminotherapie B 6 +C par voie intraveineuse (IV), auquel le medecin ajoute suivant le tableau clinique diverses medications a visee symptomatique. En 1988, une etude menee a Majuro, aux Iles Marshall, a conclu a l'efficacite du mannitol par voie intraveineuse, dans le traitement d'intoxications graves avec suspicion d'oedeme cerebral. Depuis, ce traitement a ete employe avec succes dans plusieurs regions d'endemie

From a study of the Mossbauer absorption of 57 Fe impurities substituted for Cu in superconducting YBa 2 Cu 3 O 7−δ we conclude that there are no static ordered magnetic moments within the Cu sublattices in this compound down to 4.2 K Mise en evidence de l'absence d'ordre magnetique statique au-dessus de 4,2 K

In dilute ZnS:$^{57}\mathrm{Fe}$ absorbers the isolated ${\mathrm{Fe}}^{2+}$ ions give a single M\"ossbauer absorption line at all temperatures ($1.4l~Tl~295 \mathrm{K}$), but a relaxation broadening is observed near 8 K. A convenient relaxation line-shape theory has enabled the transition rate ${W}_{{\ensuremath{\Gamma}}_{4}\ensuremath{\rightarrow}{\ensuremath{\Gamma}}_{1}}$ from the first excited spin-orbit triplet ${\ensuremath{\Gamma}}_{4}$ to the ground-state level ${\ensuremath{\Gamma}}_{1}$ to be measured between 6 and 13 K. Two additional ${\mathrm{Fe}}^{2+}$ quadrupole doublets appear for $T\ensuremath{\lesssim}5$ K in the ZnS:$^{57}\mathrm{Co}$ emission spectra. These are due to the slow relaxation contributions of the excited spin-orbit triplets ${\ensuremath{\Gamma}}_{4}$ and ${\ensuremath{\Gamma}}_{5}$ of ${\mathrm{Fe}}^{2+}$ which are then observed out of the thermal equilibrium following the decay of the radioactive parent $^{57}\mathrm{Co}$. The two transition rates ${W}_{{\ensuremath{\Gamma}}_{4}\ensuremath{\rightarrow}{\ensuremath{\Gamma}}_{1}}$ and ${W}_{{\ensuremath{\Gamma}}_{5}\ensuremath{\rightarrow}{\ensuremath{\Gamma}}_{1}}$ were obtained by following the intensities of the ${\ensuremath{\Gamma}}_{4}$ and ${\ensuremath{\Gamma}}_{5}$ lines in the emission spectra below 5 K when these rates are comparable to the inverse nuclear lifetime $\frac{1}{\ensuremath{\tau}}$. Both the absorber and source measurements of ${W}_{{\ensuremath{\Gamma}}_{4}\ensuremath{\rightarrow}{\ensuremath{\Gamma}}_{1}}$ show approximately a ${T}^{5.0}$ mean thermal variation, whereas the source measurements of ${W}_{{\ensuremath{\Gamma}}_{5}\ensuremath{\rightarrow}{\ensuremath{\Gamma}}_{1}}$ present a ${T}^{4.0}$ mean variation. These relaxation rates are attributed to Raman processes, which have been shown to follow the thermal dependence ${W}_{e\ensuremath{\rightarrow}g}\ensuremath{\propto}{(\ensuremath{\hbar}{\ensuremath{\omega}}_{0})}^{7}[6!{(\frac{{k}_{B}T}{\ensuremath{\hbar}{\ensuremath{\omega}}_{0}})}^{7}+(3)(5!){(\frac{{k}_{B}T}{\ensuremath{\hbar}{\ensuremath{\omega}}_{0}})}^{6}+(3)(4!){(\frac{{k}_{B}T}{\ensuremath{\hbar}{\ensuremath{\omega}}_{0}})}^{5}+3!{(\frac{{k}_{B}T}{\ensuremath{\hbar}{\ensuremath{\omega}}_{0}})}^{4}]$ instead of the usual ${T}^{7}$ dependence, when the temperature is smaller than the energy separation ${E}_{e}\ensuremath{-}{E}_{g}=\ensuremath{\hbar}{\ensuremath{\omega}}_{0}$ between the excited level and the ground-state level.

A detailed Mossbauer study of 170Yb diluted in CaF2 has been performed on CaF 2 (170Yb) absorbers as well as on CaF 2 (170Tm) sources. Various informations have been obtained about valency states of Ytterbium, relative proportions of the different sites, hyperfine parameters, relaxation of Yb3+, concentration and after decay effects etc— The isomer shift of Yb3+ and Yb2+ in cubic sites in CaF2 differ only by 0.29±0.10 mm s ; an accurate determination of the nuclear factor, g ( 170 Yb , 84 keV ) = 0.334±0.002 , has been derived from the slow relaxation Hf splitting of cubic Yb3+.

170Yb Mossbauer measurements show that the heavy electron compound YbAs undergoes a first order paramagnetic-antiferromagnetic transition centered at TN=0.58K. The saturated 4f-shell magnetic moments are reduced by 47% relative to the value predicted by a crystal field model. A study of the line shapes below TN in the presence of an external field shows that the RKKY exchange energy is about 20 times bigger than kB TN. These results show that YbAs presents a magnetic order frustrated by the Kondo effect.

Fe2+ impurities in ZnS blende exhibit low temperature Mossbauer spectra which are remarkably different in source and in absorber experiments. In source experiments below 5K we observed a complex quadrupole structure, which is partially due to the slow relaxation contribution of the first excited triplet Λ4 of Fe2+, whose population appears to be out of thermal equilibrium. The corresponding reduction factor q due to the dynamic Jahn—Teller coupling has been estimated to be about 0.91.

In YbPd, $^{170}\mathrm{Yb}$ M\"ossbauer measurements show that two different Yb charge states, one magnetic and one nonmagnetic, are present in essentially equal proportions. For the magnetic fraction the saturated spontaneous magnetic moment is $1.15{\ensuremath{\mu}}_{\mathrm{B}}$, which is lower than that in any of the ${\mathrm{Yb}}^{3+}$ cubic crystal-field levels, and there is no evidence of any anisotropy in the $4f$-shell charge distribution. These results suggest the presence of $4f$-conduction-band hybridization. Both above and below the ordering temperature of the magnetic fraction, the remaining Yb possess a negligibly small magnetic susceptibility and an isomer-shift value characteristic of a charge state close to ${\mathrm{Yb}}^{2+}$.

The analysis of Mossbauer absorption spectra of 170Yb in YbBe13 in the temperature range from 0.05 to 75K leads to the following conclusions: (i) Yb is trivalent in the magnetically ordered (TN=1.28K) as well as in the paramagnetic regions and its ground crystal-field state is the Gamma 7 doublet; (ii) the fast Yb3+ paramagnetic fluctuations are mainly due to the exchange RKKY interaction; (iii) the observed thermal variation of the relaxation rate implies that conduction electron scattering by the Yb ion is also present, and suggests that in YbBe13 the Yb ion has a Kondo behaviour.

The57Fe isomer shift observed in FeSb2S4 indicates a rather ionic behaviour typical for high-spin Fe2+ ions. The Neel transition occurs at 50±1 K. The analysis of the complex Mossbauer spectrum at 4.2 K supports the helicoidal magnetic structure with the magnetic moments in the (a, b) plane and with a non-commensurate propagation vector along thec axis. A sizeable anisotropy of the hyperfine field distribution is observed. The quadrupolar and magnetic hyperfine data are accounted for in the frame of a tetragonal crystal field approximation, which gives useful information on the single ion Fe2+ properties.

170Yb Mossbauer experiments in the heavy-electron compound YbSi are presented in the temperature range 0.045-100 K. Magnetic ordering of the Yb moments below 1.6 K is confirmed and a strong moment reduction in the magnetic phase is demonstrated. The crystal-field excitation is estimated to be 2.5 K. YbSi is thus a heavy-electron material where Kondo-frustrated magnetic ordering occurs due to the competition between RKKY exchange and Kondo coupling.

169 Tm Mossbauer measurements are reported for the distorted perovskite compounds TmAlO 3 , TmFeO 3 , TmCrO 3 and TmVO 3 and have been analyzed to provide information concerning the crystal field and magnetic properties of the Tm 3+ ion. Tm 3+ has no magnetic moment in TmAlO 3 and low temperature saturated moments of 0.09, 0.8 and 2.1μ B in TmFeO 3 , TmCrO 3 and TmVO 3 , respectively. In TmFeO 3 and TmCrO 3 the magnitudes and directions of the Tm 3+ moments are examined in terms of previously proposed magnetic structural models. In TmVO 3 , the crystal field properties are very different to those in the ferrite and chromite and a reorientation of the Tm 3+ magnetic moments, accompanied by a sharp increase in their size, is observed near 10 to 15 K.

We compare Mossbauer absorption and emission line shapes in the presence of electronic transitions. We show that under certain conditions, which are actually fulfilled in most cases, the emission line shape can be obtained from the absorption line shape in a straightforward manner. We emphasize that „interference terms” are present in both types of line shapes.

We describe a velocity drive for Mössbauer spectroscopy, which uses a velocity transducer with a moving magnet core positioned between two symmetrically arranged drive coils. Among other advantages this device improves the feedback performance by suppressing the fundamental resonance frequency in the moving rod.

Resume Les resistivites electriques, les susceptibilites magnetiques et les deplacements isomeriques du spectre Mossbauer de quelques composes intermetalliques cubiques de l'ytterbium et d'elements diamagnetiques (YbIn 3 , YbSn 3 , YbPb 3 et YbAl 2 ) ont ete etudies et compares. L'etude thermomagnetique a ete effectuee entre 10 et 300 K. Les valeurs des susceptibilites sont tres faibles a temperature ambiante et YbSn 3 en particulier, est diamagnetique. Les resistivites electriques ont ete mesurees entre 4 et 300 K. Les valeurs a temperature ambiante sont voisines de celle de l'ytterbium. Le deplacement isomerique de la raie de resonance de 170 Yb relatif a l'ytterbium metal, a 4.2 K, est tres voisin de celui des composes YbIn 3 , YbSn 3 , YbPb 3 , et nettement plus negatif que celui concernant YbAl 2 .

Two long-lived excited level contributions are evidenced in the emission spectra of substitutional57Fe2+ ions in CaF2. One originates from the Γ4 triplet of the5E state, whose relaxation properties are analysed by absorption spectroscopy and the other is probably emitted by the lowest Γ5 triplet of the5T2 state. Other after-effects, including a Fe+ state, are observed.

A detailed Mossbauer study of 170Yb diluted in CaF2 has been performed on CaF 2 (170Yb) absorbers as well as on CaF 2 (170Tm) sources. Various informations have been obtained about valency states of Ytterbium, relative proportions of the different sites, hyperfine parameters, relaxation of Yb3+, concentration and after decay effects etc— The isomer shift of Yb3+ and Yb2+ in cubic sites in CaF2 differ only by 0.29±0.10 mm s ; an accurate determination of the nuclear factor, g ( 170 Yb , 84 keV ) = 0.334±0.002 , has been derived from the slow relaxation Hf splitting of cubic Yb3+.

Resistivity, Hall voltage, magnetic susceptibility and Mossbauer parameters of Fe0·25NbS2 and Fe0·33NbS2 have been measured on powders and on single crystals as a function of the temperature, from ...

Analyse de la relaxation paramagnetique de Yb 3+ et interpretation en termes de comportement du Kondo de Yb 3+ . On observe une transition supraconductrice vers T c ∼0,27 K. La vitesse de relaxation de Yb 3+ au-dessous de Tc est fortement reduite par l'appariement de Cooper des electrons de conduction

The hf parameters and the relaxation rate of Yb 3+ in YbES are deduced from the 170 Yb Mossbauer spectra between 1·3 and 30 K. The shielding factors R ≅ 0·24 and σ 2 ≅ 0·61 are derived from the experiments. The thermal variation of the relaxation rate observed between 8 and 25 K shows an additional exponential term to the previously observed Orbach and Raman processes, which is attributed to an optical mode of phonons.

A series of dives was carried out to depths of 600 and 800 m seawater (msw) using baboons (Papio papio). Experiments were designed to study the effects of compression and the use of a He-N2–O2 gas mixture on high-pressure nervous syndrome (HPNS). When N2 was added to the He-O2 mixture at the beginning of a linear compression (200 msw/h), the symptoms associated with HPNS were still seen; in addition, the electroencephalogram (EEG) changes were more severe than those seen without N2. By use of an identical mixture, a 2-h exponential compression to 600 msw produced less severe signs of HPNS than the nonexponential profile. By use of a 2-h exponential compression to 600 msw and with addition of N2 at the end of compression, the HPNS that had been started under the He-O2 mixture decreased. Progressive addition of N2 during compression reduced the behavioral signs of HPNS without further EEG changes. These results show that the action of N2 is more complex than can be explained by a simple narcotic pressure antagonism and that the HPNS differed according to the gas mixture used.

Mössbauer studies show an antiferromagnetic order in sternbergite, and confirm the existence of a magnetic coupling in cubanite. According to the Mössbauer spectra, in each of these compounds all the iron atoms are in the same crystallographic site and in the same valency state, but the local symmetry seems to be different in the two compounds., L'étude par effet Mössbauer a mis en évidence un ordre antiferromagnétique dans la sternbergite, et confirmé l'existence d'un couplage dans la cubanite. A l'intérieur d'un même composé l'effet Mössbauer n'a décelé qu'un seul type de site et d'état de valence pour les atomes de fer, mais la symétrie locale du site paraît différente d'un composé à l'autre., Imbert P., Wintenberger Micheline. Étude des propriétés magnétiques et des spectres d'absorption par effet Mössbauer de la cubanite et de la sternbergite. In: Bulletin de la Société française de Minéralogie et de Cristallographie, volume 90, 3, 1967. pp. 299-303.

Mossbauer effect studies of divalent iron impurities substituting the metal ion at tetrahedral sites in cubic ZnS and hexagonal ZnS and CdS were performed. No indication of a static Jahn-Teller distortion for the isolated Fe 2+ ions was found. For the case when one next metal neighbor is also replaced by Fe 2+ or by another impurity a strong quadrupole splitting was visible already at room temperature.