Colossal room-temperature magnetoresistance in thin La1-xAgyMnO3 epitaxial films

The first thin La1 - xAgyMnO3 epitaxial films (y <= x) were grown on SrTiO3 (110) substrates with silver present in the ionized state (Ag+) only. The Curie temperatures T-C of the compositions with x = y = 0.05, x = y = 0.1, and x = 0.3 and y = 0.27 crystallizing in the hexagonal structure R3 $$($) over barc lie above or close to room temperature. The temperature dependences of electrical resistivity rho and of magnetoresistance parallel to Delta rho/rho parallel to = parallel to(rho(H) - rho(H) = 0)/rho(H = 0) parallel to pass through maxima near T-C, with the magnetoresistance being negative and reaching colossal values of similar to 7-20% in a magnetic field H = 8.2 kOe not only at T-C but also at room temperature. The magnetic moment per formula unit as derived from the saturation magnetization at T = 5 K is substantially smaller than expected for complete ferromagnetic ordering. The magnetization in fields of up to 6 kOe depends on the actual sample cooling conditions, and the hysteresis loop of a field-cooled sample is displaced along the H axis by Delta H. The above properties can be accounted for by the fact that the films are in a two-phase magnetic (ferromagnetic-antiferromagnetic) state induced by strong s-d exchange. The maximum value of Delta H was used to calculate the energy of exchange coupling between the ferromagnetic and antiferromagnetic parts of a sample. (c) 2005 Pleiades Publishing, Inc.