Effect of the A Cation Size on the Structural, Magnetic, and Electrical Properties of Perovskites (La1−xNdx)0.7Sr0.3r003nMnO3 (original) (raw)
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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.
Advanced Materials Letters, 2012
We have synthesized La 1-x Sr x MnO 3 (with x=0.3, 0.33 & 0.4) perovskite nanoparticles using mild sol-gel technique at low temperature and thereby studied the effect of nanosize on magnetoresistance. These samples were characterized using TGA/DSC, XRD, TEM, FTIR and temperature dependent magnetoresistance (MR) measurements. Powder X-ray diffraction (XRD) result confirms the formation of pure crystalline phase with rhombohedral symmetry in R-3C space group. Crystallite size increases with increase in Sr concentration. TEM analysis further supports the nanosized particles in the samples which lie in the range of 20-30 nm. Fourier transform infrared (FTIR) spectroscopy shows a broad peak at 615 cm-1 for all the samples gives an evidence for the formation of metal oxygen bond organized in to MnO 6 octahedral. The steep change in magnetoresistance (MR) at low field at low temperature is observed which is attributed to the alignment of the spins, while in the high field MR is due to the grain boundaries effect at low temperature. In the series studied, 33% Sr doped sample shows higher MR both at low temperature (-17.15) and room temperature (-3.07) than their counter parts.
Physica Status Solidi (a), 2001
Subject classification: 61.66.Fn; 72.80.Jc; S10.15 Structural, magnetic and electrical properties of oxygen-deficient La 0.6 Sr 0.4 MnO 3--d with 0 d 0.20 are presented. X-ray diffraction reveals a two-phase region separating a rhombohedral phase stable over 0 d 0.127 and an orthorhombic phase stable in the range 0.15 d 0.20. Transport and magnetic studies indicate that the magnetic coupling and the electronic properties are strongly dependent on the oxygen deficiency d. Rhombohedral samples are ferromagnetic with Curie temperature T C varying with d; T C reached a maximum of 367 K for d = 0.025 which corresponds to a 54% Mn 4+ /Mn 3+ ratio. Orthorhombic samples present an antiferromagnetic order. The magnetic interactions between manganese ions are estimated; their sign and magnitude confirms the obtained magnetic properties. The study of the electrical properties shows a semiconductor to metal transition as the temperature is lowered from 300 to 80 K for samples with oxygen vacancy 0 d 0.10. A semiconductor behavior for La 0.6 Sr 0.4 MnO 2.873 and an insulator one for 0.15 d 0.20 are observed throughout the total temperature range studied. The electronic phase diagram in the plane of the temperature vs. oxygen deficiency d has been deduced from the magnetic and electrical measurements.
Journal of Superconductivity and Novel Magnetism, 2013
We have investigated the structural, magnetic, and electrical transport properties of a series of ABO 3 -type perovskite compounds, La 0.67 Sr 0.33 Mn 1−x V x O 3 (0 ≤ x ≤ 0.15). The samples were characterized by X-ray diffraction and data were analyzed using Rietveld refinement technique, it has been concluded that these materials have the rhombohedral structure with R3C space group. The magnetization and resistivity measurements versus temperature proved that all our samples exhibit a ferromagnetic to paramagnetic transition and a metallic to semiconductor one when the temperature increases. Both the Curie temperature T C and the resistivity transition temperature T P of the composites decrease, while the resistance increases as the V content increases. It has been concluded that the electrical conduction mechanism in the metallic regime at low temperatures (T < T P ) can be explained on the basis of grain boundary effects and the single electron-magnon scattering process. Resistivity data were well fitted with the relation ρ = ρ 0 + ρ 2 T 2 + ρ 4.5 T 4.5 , whereas the adiabatic Small Polaron Hopping (SPH) and Variable Range Hopping (VRH) models are found to fit well in the paramagnetic semiconducting regime at the high temperature (T > T P ).
Physica B-condensed Matter, 2003
Structural, magnetic, magnetocaloric and magnetoresistance (MR) studies on La0.7Sr0.3Mn0.95Cu0.05O3 (No. 1) and La0.7Sr0.3Mn0.9Cu0.1O3 (No. 2) perovskites are reported. The crystal structure of the samples is rhombohedral with a change of the lattice constants depending on the Cu content. FC and ZFC thermomagnetic measurements for both compositions at low field indicate that a spin-glass-like state (or cluster glass) occurs at low temperatures and a very sharp change of magnetization around the phase-transition point. The Curie temperature, TC, does almost not depend on the content of Cu substitution. A maximum magnetic-entropy change, ΔSmax, of 1.96 and 2.07J/kgK at 13.5kOe and 350K is observed for sample No. 1 and No. 2, respectively. Therefore, they can be considered as active magnetic refrigerant materials for room-temperature applications. Electrical-resistance measurements show that both samples are metallic conductor for TTC moreover, the MR is maximal around TC.