W. Boujelben

Electrical Properties in Solid Solution Pr1—xSrxMnO3 (0 ≤ x ≤ 0.5)

We present the electrical properties of polycrystalline samples Pr 1-x Sr x MnO 3 (0 ≤ x ≤ 0.5). These properties are correlated to the ratio of the Mn 3+ /Mn 4+ cations. The transport properties of the Pr 1-x Sr x MnO 3 samples could be explained on the basis of double exchange mechanism between pairs of Mn 3+ and Mn 4+ cations, with conductivity occurring by electron hopping between manganese ions along Mn-O-Mn bonds. A semiconductor-to-metal transition is observed as a function of temperature for the mixed valence samples Pr 1-x Sr x MnO 3 (0.25 ≤ x ≤ 0.4) with a metallic-like behaviour above a critical temperature T Q. A semiconductor-like one is observed for all the range of temperature (50 to 300 K) for (0 ≤ x ≤ 0.2 and x = 0.5). Below the Curie temperature T c , for the ferromagnetic regimes, the spin disorder scattering process has been observed to play an important role in resistivity behaviour. The evolution of activated energies with the carrier concentration has been investigated.

Effect of quenching on magnetic properties of polycrystalline Pr0.5Sr0.5MnO3 perovskite manganite

Abstract The effect of quenching on the magnetic properties of polycrystalline Pr0.5Sr0.5MnO3 has been investigated. Quenching samples from 1400°C to room temperature in water (sample I) or in air (sample II) allows them to crystallize in two different systems and to exhibit different magnetic behavior at low temperature. Powder X-ray diffraction patterns for samples I and II could be indexed, respectively, in the rhombohedral perovskite structure with R 3 c space group and an orthorhombic one with Imma space group. Magnetization measurements show that both samples exhibit a paramagnetic–ferromagnetic transition at 280 K (sample I) and 265 K (sample II). At low temperature, sample I presents a ferromagnetic canted spin state or a mixture of ferromagnetic and canted phases, while sample II behaves as an antiferromagnet below 160 K.

Strontium vacancy effects upon the physical properties in lacunar Pr0.7Sr0.3-x□xMnO3 perovskite system

We studied the structural, magnetic and electrical properties of lacunar perovskite-type manganese oxides Pr 0.7 Sr 0.3-x □ x MnO 3 , where 0 0.15. The resistivity of the samples increases with x. The sample Pr 0.7 Sr 0.2 □ 0.1 MnO 3 shows a ferromagnetic insulator behaviour below a spin-canted ferromagnetic temperature (T FC ).

Deficiency effects on the physical properties of praseodymium–strontium manganite oxides

Abstract We investigate magnetic and magneto-transport properties in the defect Pr 0.7 Sr 0.3− x □ x MnO 3 (0≤ x ≤0.3) and Pr 0.7− x □ x Sr 0.3 MnO 3 (0≤ x ≤0.23) perovskite manganite oxides. Our study is to obtain more information on the different parameters that govern the magnetic and electrical properties in such samples. Powder X-ray diffraction patterns could be indexed in a rhombohedral perovskite structure with R3c space group for low x values and an orthorhombic one with Pbnm space group for high x values. Lacunar compounds exhibit different behavior which depends strongly on the vacancy type. 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). A semiconducting–metallic transition is observed for all x values in the praseodymium-deficient samples and only for low x values (0≤ x ≤0.1) in the strontium-deficient ones when the temperature decreases. At a magnetic applied field of 2 T, Pr 0.7 Sr 0.2 □ 0.1 MnO 3 exhibits a magnetoresistance effect of about 65% at 150 K while for Pr 06 □ 0.1 Sr 0.3 MnO 3 , the magnetoresistance remains constant below 250 K, equal to about 20–25%.

Effect of the Cation Size on the Physical Properties in Perovskite Manganite Oxides

We studied the structural, magnetic and electrical properties as a function of the average size of the A cation site, (r A ), in the perovskite manganite (Pr 1-y M y ) 0.7 Sr 0.3 MnO 3 oxides with y = 0, 0.1 and M = Sm, Bi. X-ray diffraction investigations show that our synthesized samples crystallize in the orthorhombic symmetry with Pnma space group. Magnetic measurements versus temperature in an applied magnetic field of 500 Oe show that all our samples exhibit a paramagnetic to ferromagnetic transition when temperature decreases. The Curie temperature T C decreases from 265 to 215 K when (r A ) varies from 1.2183 to 1.2150 A. Electrical measurements show that all samples exhibit a semiconducting to metallic transition with decreasing temperature. The electrical transition temperature decreases with decreasing (r A ).

Rietveld refinement X-ray powder data of Pr 0.7 Ba 0.3 MnO 3

Powder X-ray diffraction ~XRD! data were collected for Pr0.7Ba0.3MnO3 . This sample was prepared using the conventional solid state reaction by mixing Pr6O11 , Mn2O3 , and BaCO3 up to 99.9% purity at 1400 °C in air for 60 h. XRD analysis using the Rietveld method was carried out and it was found that this manganite sample has orthorhombic symmetry with Pnma space group. The lattice parameters are found to be a55.4900 A, b57.7578 A, and c55.5227 A.