HALL EFFECT OF La0.6Sr0.4MnO3 THIN FILMS.

M.GRANADA; B. MAIOROV; M.SIRENA; L.B. STEREN; J. GUIMPEL

Roma, Italia

Conferencia; International Conference on Magnetism; 2003

Manganese oxides A1-xBxMnO3 (A: La, B: Sr, Ba, Ca) have been extensively studied in the last years due to their colossal magnetoresistance (CMR) and half-metal character. The magnetic and transport properties of these compounds are mainly determined by the Mn3+/Mn4+ ratio fixed by x. In the 0.2<x<0.5 range, manganites have a ferromagnetic transition and present CMR around a metal-insulator transition. Many studies show that these properties are notably affected in thin films samples, due to substrates effects. In this work we present a study of the Hall effect in La0.6Sr0.4MnO3 films. Films of thickness t varying from 10nm to 200nm have been grown on (100) MgO and (100) SrTiO3 substrates by dc sputtering. Magnetoresistance and Hall voltages vs. field curves have been simultaneously measured using patterned contacts. As expected for a ferromagnetic system, two components can be deduced from the Hall resistance curves. In fact, both the ordinary and the anomalous Hall coefficients, Ro and Rs, were calculated from the measurements. From Ro we determined that the carriers have an effective hole-character and that the charge carriers density decreases as the film thickness is decreased, being systematically lower than the nominal hole-doping concentration. The anomalous Hall effect also depends on the film thickness, being big for the thinner films and almost zero for t > 100nm. The low-temperature Rs for perfect crystals is expected to be zero and so our results indicate an augmentation of the disorder degree with decreasing films thickness. Moreover, both, the Hall effect and the resistivity show evidences of localization effects at low temperatures in films thinner than 70nm. In thinner films, interfaces have larger relative weight on the films properties and therefore a major role of substrate-induced effects are observed in these films. The increasing disorder, found in the thinner films is assigned to substrate-induced strains and point defects.