Fabrication of 0-3 type manganite/insulator composites and manipulation of their magnetotransport properties

Abstract

In order to promote the technological applications of perovskite manganites, a great fundamental interest has been devoted to tailoring and/or enhancing their magnetotransport properties. Design and fabrication of manganite-based nanocomposites offer great potential to tailor the magnetotransport properties. In this work, we illustrate the promising concept of 0-3 type manganite/insulator composites (where manganite nanoparticles are uniformly and discretely embedded in a three-dimensional-connectivity insulator matrix) through the example of the La0.67Ca0.33MnO3 (LCMO)/MgO system. We present a promising strategy, which is based on the creation of core (LCMO)–shell (MgO) composite powders, for the synthesis of 0-3 type LCMO/MgO composites. A modified polyacrylamide gel method has been developed to prepare the core-shell structured LCMO/MgO composite powders. Besides its ability to create well-defined core-shell composite structures, the present gel method also allows the production of nanopowders with uniform particle size and in spherical shape. In our (1−x)LCMO/xMgO composite system, the lattice of LCMO is found to expand with rising MgO concentration x, yielding a bulk tensile strain. The increase in the tensile strain with x yields to a structural phase transition in the LCMO phase from an orthorhombic Pnma structure (x≤0.2) to a rhombohedral R3¯c structure (x≥0.3), and this structural transition leads to a relaxation of the strain. The strain effects induced by the MgO second phase exert a great influence on the ferromagnetic transition temperature TC. The composite system exhibits a percolative behavior in the conductivity, and the metal-insulator transition temperature TM-I decreases with x and is finally suppressed as the MgO content increases up to x=0.3. An enhancement in magnetoresistance (MR) is observed at low temperatures for the composites, and the low-field sensitivity of MR gets enhanced with the increase in MgO content. This work provides a promising method for manipulating the magnetotransport properties of manganites by composites with a proper insulator phase in a 0-3 connectivity fashion.

Polyacrylamide gel synthesis and photocatalytic performance of Bi2Fe4O9 nanoparticles

“…In this report, we introduce a polyacrylamide gel route to synthesize Bi 2 Fe 4 O 9 nanoparticles. Our recent work has demonstrated that the polyacrylamide gel method allows the production of high-quality nanoparticles with a uniform spherical shape [26][27][28], and also this method exhibits an excellent capability to create core-shell composite nanoparticles [26]. The photocatalytic activity of Bi 2 Fe 4 O 9 nanoparticles fabricated in the present study has been examined by the photodegradation of methyl red 0925-8388/$ -see front matter © 2010 Elsevier B.V. All rights reserved.…”

Studies on La0.67Ca0.33MnO3–SrTiO3 composites using two-phase model

“…Many groups have attempted to synthesize CMR-insulator composites, such as La 0.67 Ca 0.33 MnO 3 (LCMO)-MgO [11], LCMO-BaTiO 3 (BTO) [12,13], LCMO-Al 2 O 3 [14,15], La 0.67 Sr 0.33 MnO 3 -La 2 O 3 -La(OH) 3 [16], La 0.67 Sr 0.33 MnO 3 -polyaniline [17] and LCMO-SrTiO 3 (STO) [18], etc. Incorporation of insulating materials as a second phase is believed to be advantageous to enhance extrinsic CMR behaviour as they make the GBs insulating, thus creating a barrier in the way of the charge carriers followed by an enhancement of tunneling probability.…”

“…For a better understanding of CMR a large number of studies have been carried out in single crystals [6], thin films [7,8], polycrystalline CMR materials [9,10] and CMR-based composites [11][12][13][14][15][16][17][18]. Many groups have attempted to synthesize CMR-insulator composites, such as La 0.67 Ca 0.33 MnO 3 (LCMO)-MgO [11], LCMO-BaTiO 3 (BTO) [12,13], LCMO-Al 2 O 3 [14,15], La 0.67 Sr 0.33 MnO 3 -La 2 O 3 -La(OH) 3 [16], La 0.67 Sr 0.33 MnO 3 -polyaniline [17] and LCMO-SrTiO 3 (STO) [18], etc.…”

Magnetocaloric effect in composite structures based on ferromagnetic–ferroelectric Pr0.6Sr0.4MnO3/BaTiO3 perovskites

“…A big interest is being paid to multiferroic materials with coupled electric and magnetic properties because they can exhibit both electrical polarization induced by a magnetic field and magnetization induced by an electric field [5][6][7][8][9]. If these materials are to be used in practical applications, it is necessary to make a composite of magnetic and electric compounds with an improved magnetoelectric effect.…”