STRUCTURAL AND MAGNETIC STUDY OF PEROVSKITE MANGANITES OXIDES Pr 1-x x MnO 3

Abstract Structural and magnetic properties in a self doped Pr 1-x x MnO 3 system are investigated. X-ray diffraction patterns show that samples with composition range 0.0-0.3 crystallize in orthorhombic perovskite structure with Pbnm space group. Our samples exhibit an antiferromagnetic behavior at low temperature. The temperature ordering as a function of the vacancy content remains constant, however the magnetization magnitude at low temperature (T = 10 K) increases with increasing deficiency content

Synthesis and structure of new pyrochlore-type oxides Ln2ScNbO7 (Ln = Pr, Nd, Eu, Gd, Dy)

We report the synthesis and structural study of mixed oxides in the Ln2ScNbO7 series. New phases with Ln = Pr, Eu, Gd and Dy are obtained. All crystallize in the cubic pyrochlore structure type, space group F-d3m, with no Sc-Nb ordering on the B-site. The structures are determined by Rietveld refinement. The evolution of cell parameters, interatomic distances and angles as a function of lanthanide cation size is discussed. Magnetic measurements show the absence of ordering down to 2 K, in agreement with the presence of strong geometric frustration in the lanthanide sublattice. The europium phase shows a peculiar magnetic behaviour; its magnetic susceptibility becomes constant below ca 50 K. This feature confirms the behaviour observed previously on Eu2Ti2O7 and is ascribed to crystal field effects

Ferromagnetism in lacunar perovskite manganites Pr

Deficiency effects in the A site upon the structural, magnetic and electrical properties in the lacunar perovskite manganite oxides Pr0.7Sr$_{0.3-x}$ xMnO3 ($0\leq x \leq 0.3$) and Pr$_{0.7-x}$ xSr0.3MnO3 ($0\leq x \leq 0.23$) have been investigated. This study focuses on the different parameters which govern the magnetic and electrical properties in such samples. The powder X-ray diffraction patterns for all samples could be indexed either with a rhombohedral perovskite structure and R$\bar{3}$c space group for $x\leq 0.2$ in strontium deficient samples and for $x\leq 0.1$ for praseodymium deficient ones. For other values of x the samples could be indexed in the orthorhombic structure with Pbnm space group. Magnetic and electrical investigations show that praseodymium and strontium vacancies do not have similar effects on the lacunar compounds. Magnetization measurements versus temperature show that all our samples exhibit a magnetic transition when the temperature decreases. All the praseodymium deficient samples exhibit a paramagnetic-ferromagnetic transition when the temperature decreases while the strontium deficient ones exhibit this transition only for low x values. The magnetic transition temperature shifts to lower values as the strontium deficiency increases (from 265 K for x = 0 to 90 K for x = 0.3) and to higher values with the praseodymium deficiency increase (from 265 K for x = 0 to 315 for x = 0.23). Resistivity measurements as a function of temperature show a semiconducting-metallic transition for all x values in the praseodymium lacunar samples and only for low x values ($0\leq x \leq 0.1$) in the strontium lacunar ones when the temperature decreases

Effect of Monovalent Doping on the Structural, Magnetic and Magnetocaloric Properties in La0.7M0.2M ′ 0.1MnO3 Manganese Oxides (M=Sr, Ba and M ′ =Na, Ag, K)

AbstractStructural, magnetic and magnetocaloric effects of powder perovskite manganites La0.7M0.2M′0.1MnO3 (M=Sr, Ba and M′=Na, Ag and K) have been investigated. Our samples have been elaborated using the conventional solid state reaction at high temperature. X-Ray diffraction characterizations showed that all our synthesized samples crystallize in the distorted rhombohedral system with R3̄c space group. Magnetization measurements versus temperature in a magnetic applied field of 50 mT showed that all our samples are ferromagnetic above room temperature. From the measured magnetization data of our synthesized samples as a function of magnetic applied field, the associated magnetic entropy change close to their respective Curie temperature TC and the relative cooling power RCP have been determined. A maximum magnetic entropy change, |ΔSMMax|, of 4.07 Jkg−1 K around 345 K was obtained in La0.7Sr0.2Na0.1MnO3 sample upon a magnetic field change of 5 T. The |ΔSMMax| values of La0.7Ba0.2M′0.1MnO3 are smaller in magnitude compared to La0.7Sr0.2M′0.1MnO3 samples and occur at lower temperatures

Electron spin resonance in heavily doped TMMC : Cu

We report ESR measurements in the one-dimensional Heisenberg paramagnet (CH3)4NMn1-xCuxCl3 for x ranging between 0 and 0.5. The room temperature results show a maximum of the linewidth for a concentration x ~ 0.25, in agreement with the altered diffusion model, with the notable exception of the magic angle orientation. A lineshift towards low fields is observed in strongly doped samples. At lower températures, ESR is also modified by the impurities, in accordance with the réduction of the short time effects and the enhancement of the diffusive contribution.Nous donnons les résultats de mesures de RPE dans le paramagnétique de Heisenberg unidimensionnel (CH3)4NMn1 -xCuxCl 3, x étant compris entre 0 et 0,5. A température ambiante la largeur de raie est maximum pour une concentration x ~ 0,25 en accord avec le modèle de la diffusion freinée. On note cependant une exception pour l'orientation correspondant à l'angle magique. On observe un déplacement de la raie vers les bas champs dans les échantillons les plus dopés. La RPE est aussi modifiée par les impuretés aux basses températures. Les mesures sont en accord avec une réduction de la contribution gaussienne et une augmentation de la contribution diffusive