Comparative Hall studies in the electron- and hole-doped manganites La0.33Ca0.67MnO3 and La0.70Ca0.30MnO3

A comparative study of the Hall effect and the longitudinal resistivity of La1-xCaxMnO3 (x= 0.30 and x =0.67) thin films has been performed. The under doped samples (J=0.3D) show a semiconductor-to-quasimetal transition, and a colossal magnetoresistance (CMR) effect around T-C= 280 K. The samples wit h x= 0.67 stay semiconducting at low temperatures, and show a CMR effect up to 99% in magnetic fields of 50 T. In both compounds an extraordinary Hall contribution was found, with opposite sign to the regular Hall effect. For x= 0.30 the charge carriers are hole-type, whereas for x = 0.67 we observe electron-type carriers. The extraordinary Hall coefficient R-A can be link ed to the longitudinal resistivity rho (xx) via R(A)(proportional to)rho (p roportional to)(xx) with a = 1.38 for x= 0.30, and alpha= 0.60 for x= 0.67.