Physical properties of the giant magnetoresistive perovskite system La-Er-Ca-Mn-O

Abstract. The effect of minor changes in lattice parameters and Mn 3+ /Mn 4+ ratios on the magnetoresistive and related properties of the La-Er-Ca-Mn-O perovskite system have been investigated. The latter is found to be the more important factor in determining the magnetotransport properties of these materials. One composition has been prepared by both the standard ceramic method as well as a sol-gel technique. Although the general features of the magnetotransport properties of these two samples were very similar, the magnetic properties showed significant differences. Experimental results are explained on the basis of a spindependent mechanism which is related to lattice distortion

Allergies alimentaires chez l'enfant (le choc anaphylactique : une urgence médicale)

MONTPELLIER-BU Pharmacie (341722105) / SudocSudocFranceF

Magnetic and Mössbauer studies of quasicrystalline Al70−xPd15T15Mx (T = Mn, Fe; M = Si, Ge; 0 ≤ x ≤8)

Our magnetisation and Mössbauer effect investigations of magnetic icosahedral quasicrystals (Al, Ge)70Pd15Mn15 and (Al, Si)70Pd15Fe15 have shown that the magnetic atoms Mn and Fe occupy two types of sites, one of which is magnetic and one which is non-magnetic. In certain cases the magnetic atoms couple ferromagnetically© Elsevie

Magnetoresistance studies of La0.6M0.07Ca0.33MnO3 (M=Er, Yb, Bi) perovskites

Magnetotransport and magnetic properties of the system La0.6M0.07Ca0.33MnO3(M=Er, Yb, Bi) have been investigated. The behavior of the three samples varies much more than might be expected on the basis of the similarity in ionic radii of M3+ ions and a small quantity of the substitution. A strong correlation is found between magnetization data, FMR and transport behavior. These results are discussed in terms of minor variations in lattice properties and differences in chemical properties, such as ionic radii and electronegativity, which influence the exchange mechanisms. The Bi containing compound is particularly interesting from an applications stand point, as it shows a sharp transition at around 265 K. (C) 1997 Elsevier Science S.A

Magnetic and electronic properties of the magnetoresistive perovskites La0.67−xBixCa0.33MnO3

Magnetotransport, magnetic susceptibility and ferromagnetic resonance (FMR) studies of La0.67−xBixCa0.33MnO3 perovskites with x=0.03 to 0.16 are reported. The magnetoresistivity ratio shows a peak in all samples corresponding to the Curie transition. In samples with xgreater-or-equal, slanted0.13 a second peak at lower temperature is seen in the magnetoresistivity. Magnetic susceptibility measurements show Curie like behavior for all samples. Samples with low Bi content show a difference between field cooled and zero-field cooled measurements at low temperature. This difference diminishes with increasing x. FMR spectra show a single resonance above Tc. Samples with small Bi content show two resonances just below Tc but these resonances cannot be clearly resolved at lower temperatures due to line broadening. These two resonances also become less resolved with increasing x. No anomalous behavior corresponding to the low-temperature peak in the magnetoresistivity is seen in the magnetic susceptibility or FMR measurements. Results are interpreted in terms of the effects of Bi on the structure of grain boundaries.© Elsevie

Nature and entropy content of the ordering transitions in RCo2

Differential scanning calorimetry experiments have been performed under magnetic field in R Co 2 Laves phases compounds ( R = Pr , Nd, Tb, Dy, Ho, and Er). The thermodynamical nature of the ferromagnetic transitions in Pr Co 2 and Nd Co 2 is clarified, after the controversy present in the literature about the character of their ordering transitions. The magnetocaloric effect in the compounds showing a first-order magnetostructural transition ( R = Dy , Ho, and Er) is characterized. The latent heat, L , and the entropy change at the transition, Δ S , have been studied by inducing the transition sweeping the temperature at a constant field and sweeping the field at a constant temperature. Results from calorimetric data show that L is essentially temperature independent, suggesting that the first order transitions in R Co 2 are dominated by the structural effects. The magnetocaloric effect has been also characterized from magnetization data and the results are in excellent agreement with those from calorimetric data. However, the corresponding values of Δ S for isothermal and isofield experiments differ significantly. We interpret the differences in terms of the broadness of the transitions and prove that the various Δ S values reported in literature for first-order transitions are not always directly comparable