Pressure-induced variation of the magnetic structure of the surface of La0.6Sr0.4MnO3 granules

The transport properties of textured films and tunneling junctions of La0.6 Sr0.4MnO3 , defined by the surface state of the granule, are studied in low magnetic fields (below 100 Oe) and at pressures of up to 10 kbar. Tunnelin g junctions of two types are investigated, namely, mechanical break junctio ns and La0.6Sr0.4MnO3-insulator-superconductor junctions. Although only one electrode represents the magnetic material in the latter case, all samples exhibit a low-field magnetoresistive effect. Hydrostatic compression suppr esses the magnetoresistive effect to considerably change the transport prop erties of ceramic and tunnel samples. The reasons for such behavior are dis cussed in connection with the model of spin-polarized inelastic tunneling o f charge carriers through a potential barrier formed both by the intergranu lar region and by the surface of contacting granules. Reasons are given for the fact that it is most probable that the magnetic state of the barrier a nd its height vary under the effect of pressure because of the transition o f the surface of granules to the metallic state. (C) 2001 MAIK "Nauka/Inter periodica".