Solution sol–gel processing and investigation of percolation threshold in La2/3Ca1/3MnO3:xSiO2 nanocomposite

Abstract

The composites of La 2=3 Ca 1=3 MnO 3 :xSiO 2 (0pxp0:40) have been synthesized by sol-gel technique to derive homogeneous nanocomposites. Si 4þ by virtue of its strong preference for tetrahedral site does not enter the perovskite lattice. The percolation threshold composition has been determined by resistivity measurements at around 90% volume fraction of LCMO. A detailed electrical, magnetic and magneto-transport characterizations have been carried out for composites around the threshold composition (x ¼ 0:05; 0:10; 0:15). The magnetoresistance results at 1 T show a sharp peak at T c and a minimum just below T c as reported in several polycrystalline LCMO composites.

Enhanced low-field magnetoresistance in La0.7Ca0.3MnO3+x(ZnO) composites

“…We suggest that the grain size, the connectivity and the volume fraction of the grain boundary, and special physical property of ZnO semiconductor material may be the main factors. Our result accords with Das' work [18].…”

“…From Fig. 6, we can also see that with increasing x, σ S decrease, because of the decrease of the ferromagnetic LCMO grains volume fraction, which can be seen in many magnetic/insulates composites [5,6,18].…”

“…This phenomenon was very common in other manganites doped with high resistivity phase [6][7][8][9]. In ρ-T curves, an insulator-metal transition at a higher temperature (noted as T P1 ) was observed, which can be explained by the double-exchange (DE) mechanism in LCMO grains [16][17][18][19][20]. With increasing ZnO concentration, T P1 was nearly no change and the values of different samples approximately equaled to the T P of pure LCMO.…”

Structure and properties of La–Ca–Mn–O composites prepared by the glass-ceramic method

“…These results clearly show that the equivalent volume of LCMO phase is ≤30% in all the cases with the rest comprising of nonmagnetic SiO 2 based phase. Similar LCMO:SiO 2 composites made by sol-gel technique however, do not show a decrease in T c but a slightly reduced magnetization [13], indicating that the nature of magnetic disorder in the present liquid quenched composites is very different. The presence of a kink in the magnetization (Fig.…”

Magnetotransport in La0.7Ca0.3MnO3–PMMA composites synthesized by polymeric precursor route

“…Consequently several types of composites have been studied e.g. La 2/3 Sr 1/3 MnO 3 -CeO 2 [12], La 2/3 Ca 1/3 MnO 3 -SrTiO 3 [15], La 0.7 Sr 0.3 MnO 3 -glass [16], La 2/3 Ca 1/3 MnO 3 /La 0.7 Sr 0.3 MnO 3 -ZnO [17,18], and various other systems [19][20][21]. In addition to these, some studies have also been carried out on manganite-polymer composites [22][23][24][25][26].…”