Materials based on doped rare-earth manganites can significantly change their electrical resistance in an applied magnetic field. This is the so-called colossal magnetoresistance effect. These materials can be used in different magnetoresistive sensors and devices, such as ultrahigh-density read heads for magnetic memory, metal detectors, compasses, linear and angular position sensors, temperature detectors, and bolometers.

The colossal magnetoresistance effect is observed in manganite crystallites. A way to increase the total magnetoresistance of such materials is to obtain composites with thin dielectric films between conductive ferromagnetic particles; in this case, the tunnel magnetoresistance effect occurs.

The amorphous precursors was synthesized by preliminarily annealing a mechanical mixture of manganese( III) and lanthanum(III) oxides, boric acid, and strontium carbonate of the nominal compositions La0.67Sr0.33MnO3 + xSrB2O4 (x=0,32; 0,56; 0,86; 1,00; 1,10; 1,30; 1,59; 1,95) at 800°C. Then, the precursor was pressed into pellets 1 cm in diameter, which were melted with an arc burner. The melt was quenched between copper plates. The glasslike samples thus prepared were annealed at 850 - 1000°C for 2 or 24 h.

X-ray powder diffraction showed that the glassceramic samples contain mainly two crystalline phases (La,Sr)MnO3 and SrB2O4.

The field dependence of the sample resistivity was measured by the standard four-probe technique at 77 K and 297 K. The negative magnetoresistance was as large as 14,4% at 80 kA/m, 77K and 6,2% at 40 kA/m, 297K. It is worth noting that a low electrical resistance (tens of ohms) and the magnetoresistance effect were observed at a relatively small manganite content. This is likely due to the microstructure features of the sample, in which the interpenetration of the manganite and borate phases ensures good percolation.

1. POSTER: Synthesis and properties of a (La,Sr)MnO_{3-x} -based magnetoresistive composites from borate glasses., Microsoft Office Document, 5.5MB

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