Simultaneous observation of tunnel-type GMR and intrinsic CMR in nanometer perovskite

The nanometer-sized perovskite L80.85 Sro.15 MnO3 is synthesized by a sol-gel method. And, through controlling the conditions of heat-treatment, a series of polycrystalline perovskite with different grain sizes is obtained. The resistance measurements with changing temperatures show that with the increase in grain size the transport properties of this kind of granular perovskite, including the giant magnetoresistanee (GMR) effect, systematically change from an interfacial effect-controlled form to the crystal intrinsic type. Meanwhile, the magnetoresistance effect transforms from an interfacial tunneling GMR to the intrinsic colossal magnetoresistance (CMR). For the sample with a suitable grain size (≈100 nm), the two magnetoresistance effects can be observed simultaneously. And the action of both magnetoresistances in common can make a “plain” on the curve of magnetoresistance versus temperature (MRT); that is, the magnetoresistance effect of the granular perovskite does not change with temperature in a wide range.