Effect of the A Cation Size on the Structural, Magnetic, and Electrical Properties of Perovskites (La 1x Nd x ) 0.7 Sr 0.3 MnO 3 (original) (raw)
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Journal of Solid State Chemistry, 2002
An intense e4ort has recently been devoted to studying the interplay between structure, magnetism, and transport in manganese perovskite Ln 1؊x A x MnO 3 (Ln ؍ La, Pr, Nd, Sm; A ؍ Ca, Ba, Sr). As a function of temperature, applied magnetic 5eld, doping, A-site ionic radius 1r A 2, and A-site size disorder, this system displays a rich phase diagram for both magnetotransport and structural properties. We have investigated the structural, magnetic, and transport properties of (La 1؊x Nd x ) 0.7 Sr 0.3 MnO 3 . The crystal structure was examined by X-ray powder di4raction which indicated that all the samples were single phase and revealed a transition from rhombohedral to orthorhombic structure with increasing x. The magnetization and resistivity investigation shows that for all values of x, (La 1؊x Nd x ) 0.7 Sr 0.3 MnO 3 are ferromagnetic+metallic at low temperatures and paramag-netic+semiconductor above the Curie temperature T c .
Materials Science and Engineering: B, 2007
We have investigated the effect of nominal strontium deficiency on the structure and the magnetic properties of La 0.6 Sr 0.4−δ MnO 3 (0 ≤ δ ≤ 0.3) manganese perovskites. The polycrystalline samples have been elaborated by the conventional ceramic method at 1573 K. The morphology, grain sizes and chemical analysis were analyzed by scanning electron microscope (SEM) and energy dispersive X-ray (EDX) techniques. The refinement of the structure by the Rietveld method revealed that most of these compounds crystallize in a rhombohedral (R3c) perovskite structure. Magnetization as a function of temperature, M(T), shows that these compounds exhibit a paramagnetic (PM) to ferromagnetic (FM) phase transition with decreasing temperature. The Curie temperature (T C ) decreases from 361 K to nearly the room temperature (292 K) with decreasing nominal strontium content. In the paramagnetic region the inverse of the magnetic susceptibility was fitted by a Curie-Weiss law. Magnetization as a function of magnetic field, M(H), measured at 50 K shows that all compounds are FM with a maximum in the magnetic saturation moment for the nominal value δ = 0.12. A comparative analysis shows that nominal vacancies, δ, cannot generally be achieved by our conventional ceramic method and results in a shift of the perovskite manganite composition compensated by the formation of an additional Mn 3 O 4 phase.
Effect of Cr doping in Structure and Magneto-transport Properties of (La0. 67Sr0. 33) MnO3
The study of perovskite manganites La 0.67 Sr 0.33 Mn 1-x Cr x O 3 (0≤ x ≥0.10) has been carried out. The structure and magneto-transport properties of La 0.67 Sr 0.33 Mn 1-x Cr x O 3 manganites are strongly dependent on the substitution level x. Polycrystalline samples of La 0.67 Sr 0.33 Mn 1-x Cr x O 3 (0≤ x ≥0.10) were prepared by solid state reaction method. The little difference between the ionic radii of Cr 3+ and Mn 3+ causes no change in the structure, the structure remains rhombohedral. The temperature dependence of the resistivity is measured from 5-400 K without and with magnetic field up to 5 T. The value of metal-insulator (M-I) transition temperature (T P) decreases when resistivity increases for all the samples while doping level x increases. The value of magnetoresistance (MR %) increases with increases Cr doping level for all samples. We have calculated energy band gap (E g) for all samples and it is revealed that as per doping level increases E g increases which is comparable with experimental data. So, the structure and magneto-transport behavior affected by Cr substitution.
Journal of Alloys and Compounds, 2009
We investigate the effect of potassium doping on the structural, magnetic and magnetocaloric properties of La 0.7 Sr 0.3−x K x MnO 3 (x = 0.05, 0.1, 0.15 and 0.2) powder samples. Our polycrystalline compounds were synthesized using the solid-state reaction at high temperature. X-ray diffraction characterizations showed that all our studied samples crystallize in the distorted rhombohedral system with R3c space group. With increasing potassium content, the unit cell volume exhibits a broad maximum around x = 0.15. Magnetization measurements versus temperature showed that all our samples exhibit a paramagnetic to ferromagnetic transition with decreasing temperature. The Curie temperature T C is found to decrease from 365 K for x = 0 to 328 K for x = 0.2 as well as the saturated magnetization M sp which shifts from 3.68 B /Mn for x = 0 to 3.05 B /Mn for x = 0.2. The critical exponent defined as M sp (T) = M sp (0)[1−(T/T C)] is found to remain almost constant and equal to 0.33 for all our samples. The maximum of magnetic entropy changes | S max | of La 0.7 Sr 0.3−x K x MnO 3 for x = 0.05 and 0.15 is found to be respectively, 1.37 and 1.2 J kg −1 K −1 under a magnetic field change of 1 T.
Chemistry of Materials, 1997
The layered manganite La 1.2 Sr 1.8 Mn 2 O 7 is important in that it displays giant negative magnetoresistance properties, and its study complements the growing body of what we know about the complex size-charge-temperature-magnetic field parameter space of the perovskites A III 1-x A′ II x MnO 3. We report here the results of a detailed characterization of the microstructure and structure of this layered phase by high-resolution electron microscopy and synchrotron X-ray powder diffraction (SXPD). The high resolution of the data has permitted the quantification of stacking faults. The SXPD data have also been treated using Rietveld analysis. We reexamine the magnetic and transport properties of this phase. The study highlights the importance of the two-dimensional (2D) nature of the title phase.
Ionics, 2018
In order to study the effect of A-site cation mismatch on the structural, magnetic, and transport properties, a systematic investigation of La 0.7 Ca 0.25 A 0.05 Mn 0.8 Cr 0.2 O 3 (A = Ca, Li, Na, K) has been undertaken. The XRD data of the materials, prepared by glycine-nitrate combustion method, have been analyzed by Rietveld refinement technique. The iodometric and EDX results show that except K doped sample, the desired stoichiometry of all the phases remains the same. The phases display a paramagnetic to ferromagnetic transition at low temperature with T c found to decrease with decreasing ˂r A ˃. It has been concluded that the conduction mechanism was dominated by small polaron hopping model in the high temperature paramagnetic semiconducting region.
Magnetic and Magnetoresistive Properties of Double Perovskite Oxides RE-SrMnCoO $_{6}$ (RE = Nd, La)
IEEE Transactions on Magnetics, 2009
Polycrystalline samples of NdSrMnCoO 6 and LaSrMnCoO 6 have been synthesized by sol-gel technique and were characterized by means of x-ray diffraction (XRD). The Rietveld refinement of the XRD data confirms the single phase nature of the samples. These oxides have cubic crystal structure (space group Fm 3m) at room temperature. The magnetization data measured in a field of 100 Oe, under zero field cooled and field cooled conditions, show thermomagnetic irreversibility below 210 K. The electrical resistivity of these samples increase with decreasing temperature from 300 K down to 80 K. The conduction above 115 K can be described by variable range hopping mechanism. A maximum magnetoresistance (MR) of about 5% and 11% are achieved at 90 K in an applied field of 7 T for NdSrMnCoO 6 and LaSrMnCoO 6 samples, respectively, and MR has a negative sign. Index Terms-Double perovskite oxides, electrical transport and magnetic properties.