Colossal Magnetoresistance in La_0.7Ca_0.3MnO_3-δ:  Comparative Study of Single-Crystal and Polycrystalline Material

Abstract

The magnetoresistance (MR) and transport properties of both single-crystal and polycrystalline samples of La 0.7 Ca 0.3 MnO 3-δ (LCMO) have been investigated to elucidate their magneto transport behaviors near and below the Curie temperature T C . We find that negative MR is heavily dependent upon the surface morphology in the low-temperature, ferromagnetic regime. The polycrystalline sample postannealed at 1400 °C under the oxygen atmosphere exhibits large low-field MR in the whole temperature range below T C , which is about 20% at 0.5 T. On the other hand, the single-crystal sample shows the remarkable suppression of resistivity only at the narrow temperature region near T C . We suggest that the MR found in the polycrystalline sample is dominated by the tunneling of spin-polarized electrons between grains below T C while the MR in the single crystal is mainly ascribed to the suppression of spin fluctuation. The difference in the MR property between the single-crystal and polycrystalline samples is discussed in terms of oxygen inhomogeneity and granular effects affected by interfacial melting.

Influence of processing conditions on the crystal structure and magnetic behavior of La0.7Ca0.3MnO3±δ samples

“…The obtained data indicate that all samples have the perovskite structure with the Pbnm space group. Crystallographic cell parameters are in good agreement with results observed in studies using alternative preparation methods [18,19].…”

“…One way to study chances in the oxygen content is the production of slightly lanthanum deficient samples, although this procedure leads to a decrease in the critical temperature for sol -gel prepared samples [20]. Otherwise, chemical methods produce samples whose characteristics, such as reactiveness and homogeneity, allow to study the effect of variations in the oxygen stoichiometry [5,19]. In Table 1 it is also possible to observe the oxygen stoichiometry data obtained by TG -DTA and AAS analyzes, in agreement to values presented for samples prepared by sol-gel techniques [4,20].…”

Anisotropic behaviour in the magnetic field dependence of the low temperature electrical resistance of calcium-doped lanthanum manganate thin films grown by RF magnetron sputtering

“…On the contrary, the film grown on MgO displays a significant magnetoresistance in a much wider temperature range, i.e. from the transition temperature down to 20 K. Comparison with literature data [8,18,23] indicates that the properties of the (100)-oriented film grown on LaAlO 3 are similar to those of bulk single crystals and epitaxial thin films, while the behaviour of the film grown on MgO is typical of polycrystalline films and bulk compounds.…”

“…In the case of the film grown on LaAlO 3 , only (h00) pseudo-cubic reflections were observed in the X-ray diffraction pattern. [23] and epitaxial thin films [8,24,25], whereas the low temperature resistivity of the film grown on MgO is two orders of magnitude larger. This suggests that the contribution of possible small-angle grain boundaries [26] or microstructural defects [24] to the overall electrical resistance of the film grown on LaAlO 3 remains limited.…”

La2/3Ca1/3MnO3Nanoparticles with Novel Magnetoresistance Property

“…[1][2][3] In particular, synthesis of La 1-x Ca x MnO 3 (LCMO) nanoparticles is very important not only for fabricating electrodes and thin film, but also for understanding the CMR phenomenon. 4,5 However, obtaining the LCMO nanoparticles through the conventional solid-state reaction is very difficult since a temperature of more than 1200 ºC is usually required to achieve the LCMO crystal with single phase.…”