Colossal Room-Temperature Magnetoresistance in Thin La[sub 1 – ][sub x]Ag[sub y]MnO[sub 3] Epitaxial Films

Abstract

The first thin La1−x AgyMnO3 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 $$R\bar 3c$$ above or close to room temperature. The temperature dependences of electrical resistivity ρ and of magnetoresistance ¦Δρ/ρ/¦ = ¦(ρH − ρ H = 0)/ρH=0¦ pass through maxima near T C, with the magnetoresistance being negative and reaching colossal values of ∼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 ΔH. 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 Δ H was used to calculate the energy of exchange coupling between the ferromagnetic and antiferromagnetic parts of a sample.