REENTRANT METAL-INSULATOR-TYPE TRANSITION INDUCED BY HIGH FLUENCE CHROMIUM ION-IMPLANTATION OF LA0.7CA0.3MNO3 THIN-FILMS

Thin films of colossal magnetoresistance (MR) material La0.7Ca0.3MnO3 were implanted with 200 keV Cr ions over a range of fluence from 1X10( 13) to 5 X 10(15) ions/cm(2). Resistance measurements were made in zer o and applied magnetic fields of up to 8 T. At fluences of 1 X 10(14) and 5 x 10(14) Cr+/cm(2), the resistance was much greater than in the unimplanted material and the metal-insulator transition temperature wa s suppressed to values below 20 K. For the highest fluence (5 x 10(15) ions/cm2), a reentrant metal-insulator-type transition was observed a nd the resistance dropped significantly. Furthermore, improvement in t he low-field MR was observed between the virgin and high fluence impla nted films for fields less than 500 mT. These results are interpreted in terms of changes in magnetic properties with depth, defect creation : and the influence of oxygen deficiency. (C) 1998 American Institute of Physics.