Elastic magnetoresistive materials based on polyethylene

Composite materials can often exhibit properties that are not typical for their individual components. New properties of such materials are of both physical and practical interest. In this article, the improper magnetoresistive and piezoresistive properties of new composite materials of the composition polyethylene/graphite/manganite La0.7SrO3MnO3 have been experimentally studied. The components of these materials are low density polyethylene, natural large-size graphite crystal, and manganite La0.7SrO3MnO3. The samples were examined by X-ray diffraction and electron microscopy. We also determined the magnitude of the magnetoresistive effect of the synthesized samples in a magnetic field up to 15 kOe in the geometry of the current along the field and perpendicular to the magnetic field strength. Investigations of extrinsic piezoresistive properties were carried out under the influence of uniaxial pressure up to 275 kPa, applied parallel to the direction of the current, in the region of elastic deformation. X-ray structural analysis showed an increase in the degree of crystallinity of the polyethylene matrix from 55% before synthesis to 90% after synthesis. Depending on the ratio of the components, these composites exhibit either positive or negative magnetoresistive effect. Thus, in the composite 15% polyethylene/55%graphite/30% La0.7SrO3MnO3, the most significant positive magnetoresistive response of about 7.5% due to the diamagnetism of graphite, in a constant magnetic field H=15 kOe is achieved. The largest values of extrinsic negative piezoresistivity, reaching 45% at a uniaxial pressure of 275 kPa, are observed in the samples containing polyethylene and one of the conductive phases, namely graphite or manganite. Polyethylene/La0.7SrO3MnO3 composites synthesized near the percolation threshold exhibit a small negative magnetoresistive effect (2%) in a field of 15 kOe, associated with spin-dependent electron tunneling of La0.7SrO3MnO3.