Anomalous magnetoconductivity of epitaxial Nd0.7Sr0.3MnO3 and Pr0.7Sr0.3MnO3 films

In Nd0.7Sr0.3MnO3 films, ranging in peak resistivity from 1000 Ohm . cm to less than or equal to 1 Ohm . cm, and exhibiting large magnetoresistance effects, the zero-field resistivity above the peak temperature T-p exhibits thermally activated behavior with an activation energy of 0.115+/-0.005 eV. At T well below T-p, the magnetoconductivity, rather than the magnetoresistance, is linear in B and this linear dependence is observed over a wide B range even when the magnetization is essentially saturated. A cross-over from the linear relation to sigma increasing as B-2 is observed near and above T-p. A tentative model is proposed.Physics, Condensed MatterSCI(E)26ARTICLE7599-6049