Magnetoresistive studies on nanocrystalline La0.8Sr0.2MnO3+δ manganite

Abstract

a b s t r a c tLow-temperature magnetoresistance (MR) measurement has been carried out on nanocrystalline La 0.8 Sr 0.2 MnO 3+d manganites prepared by combustion synthesis. This preparation method yields voluminous powders with large surface area ($40 m 2 /g) having crystalline nanosize ($50 nm) products. Formation and homogeneity of the solid solutions have been confirmed by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). Rietveld refinement of X-ray data indicates that as-formed compound exhibits cubic phase with space group Pm3 m. However, calcined sample transforms into rhombohedral phase with space group R-3c. The stabilization of the cubic phase in as-formed manganite is due to the substitution of Sr 2+ on La 3+ sites, resulting in higher Mn 4+ content. The low-temperature resistivity measurements down to 70 K exhibit a broad metal-insulator transition (T MÀI ) at around 257 K. MR measurements on sintered pellets show $5% MR at 1 T, whereas for 4 and 7 T, the %MR values are found as 22% and 28%, respectively, at T MÀI .

Magnetic Properties of Interacting La0.67Sr0.33MnO3 Nanoparticles

“…Annealing the samples at 550°C and 600°C will decrease the above peaks; this is the indication of decomposition of SrCO 3 at 550°C. The absorption peaks around ν 3 ≈ 600 cm −1 and ν 4 ≈ 400 cm −1 should belong to stretching, ν 3 and bending, ν 4 of the internal phonon modes of MnO 6 octahedral [23][24][25]. The stretching mode is related to the change of Mn-OMn bond length and the bending mode involves the change of Mn-O-Mn bond angle.…”

Superparamagnetic behavior of La0.67Sr0.33MnO3 nanoparticles prepared via sol–gel method

“…3, the absorption peaks around 3450 and 1650 cm À1 are of the carrier KBr (H 2 O) n [18]. In sample S1, the two strong peaks at 860 and 1450 cm À1 belong to SrCO 3 [19,20]. Calcinations of these powders at 550 1C will decrease the above peaks; this is the indication of decomposition of SrCO 3 at 550 1C.…”

“…The absorption peaks around n 3 E600 cm À1 and n 4 E400 cm À1 should belong to stretching, n 3 and bending, n 4 of the internal phonon modes of MnO 6 octahedral [18][19][20]. The stretching mode is related to the change of Mn-O-Mn bond length and the bending mode involves the change of Mn-O-Mn bond angle.…”

Effects of pH and sintering temperature on the synthesis and electrical properties of the bilayered LaSr2Mn2O7 manganite prepared by the sol–gel process

“…MnO 6 in the crystalline structure of manganite has nearly-ideal octahedral symmetry with six vibration modes but only two are IR-active. The band around 600 cm -1 corresponds to the stretching mode (m 3 ) of Mn-O-Mn or Mn-O bonds, while the bending mode (m 4 ) around 400 cm -1 is due to changes in the Mn-O-Mn bond angle [27][28][29][30]. Appearance of the stretching and bending modes in the transmission spectra for all samples indicate that the structure of LaSr 2 Mn 2 O 7 is formed.…”