TRANSPORT AND MAGNETISM CORRELATIONS IN THIN-FILM FERROMAGNETIC OXIDES

To determine the T-c dependence of the colossal magnetoresistance (CMR ) exhibited by the ferromagnetic La(0.7)A(0.3)MnO(3+delta) (A=Ba, Ca, Sr) system, we examine the magnetic-field and temperature-dependent re sistivity and magnetization of a series of thin films that were grown via pulsed-laser deposition. The films had magnetic ordering temperatu res (T-c) ranging from 150 to 350 K. All samples display a large negat ive MR that is largest near T-c, and samples with a low T-c display si gnificantly larger MR values than do samples with large T-c's. The qua ntity rho(T-c)/rho(4 K), the amount by which the resistivity is reduce d by full ferromagnetic order, varies as exp(E(a)/T-c) with an activat ion energy E(a)=0.1 eV. These results indicate that the magnitude of t he CMR effect in a given specimen is controlled not by rho(T-c), but b y T-c via the ratio rho(T-c)/rho(4 K). Phenomenological scaling relati onships are also reported that link rho(H, T) to both H and M(H, T). ( C) 1996 American Institute of Physics.