Colossal magnetoresistance magnetic tunnel junctions grown by molecular-beam epitaxy

Using molecular-beam-epitaxy growth techniques, we have synthesized ferroma gnet/insulator/ferromagnet trilayer heterostructures with the "colossal" ma gnetoresistance material La1-xSrxMnO3 as the ferromagnet. These trilayer fi lms were fabricated into magnetic tunnel junctions which exhibit magnetores istance Delta R/R(H) of as much as 450% in 200 Oe applied field at 14 K, an d which persists up to similar to 250 K. In situ reflection high-energy ele ctron diffraction (RHEED) allows us to correlate the quality of the epitaxi al growth with the magnetoresistive properties. Samples which showed signs of disorder in RHEED also exhibit disorder effects in low-temperature trans port and have smaller magnetoresistance which vanishes at lower temperature s. (C) 2000 American Institute of Physics. [S0003-6951(00)01014-7].