Institute of Molecular Physics, Polish Academy of Sciences,

Smoluchowskiego 17, 60-179 Poznañ, Poland

We report on very large tunneling magnetoresistance (TMR), up to 600% at low-fields (<200 Oe) and at room temperature, for tunnel junctions made of the conventional La_0.7Sr_0.3MnO₃ ceramic perovskite. The associated field sensitivity reaches 3%/Oe. The spin polarization, which can be deduced from TMR value using Julliere formula, is up to 87%. This result can be important both from the basic and the technological point of view. The Curie temperature is 355 K and the coercive field is 16 Oe at RT. The high value of the tunneling magnetoresistance is obtained for a break junction and ascribed to the intergrain tunneling process. The first criterion of the tunneling like conduction mechanism is the nonlinearity of the current-voltage characteristic, I-V. The non-ohmic behavior was confirmed for all junctions with the resistance exceeding 1 kOhm. Fig. 1 shows a series of experimental I-V curves collected at various external magnetic fields at RT. The magnetic field was applied in the plane of the fracture, perpendicularly to the current direction. It is evident that the magnetic field dramatically modifies the resistance of the junction.