Effect of ion-irradiation-induced disorder on the low-field magnetoresistance of La(0.67)A(0.33)MnO(3) (A = Sr, Ca)

We report on a systematic study of the correlation between the disorder pro duced by ion irradiation and the magnetoresistance (MR) behavior of two dop ed manganite films: a highly textured La0.67Sr0.33MnO3 film on a (100) LaAl O3 substrate and a film of La0.67Ca0.33MnO3 on a YSZ substrate with a high degree of large-angle grain boundary disorder. The films were grown via met al organic chemical vapor deposition and exposed to irradiation of 200 keV Ne ions. The temperature and field dependence of the resistivity were measu red on the same samples at different levels of damage. For the Sr-doped fil m, the bulk magnetic properties were observed to degrade faster with cumula tive damage than transport. For both films at low temperature, a low-field hysteretic MR was either induced or enhanced by ion damage. These effects a re discussed in terms of diffusive transport through "granular'' magnetical ly disordered regions. (C) 1999 American Institute of Physics. [S0021-8979( 99)48608-6].