A comparative study of the Hall effect and the longitudinal resistivity of ${\mathrm{La}}_{1-x}{\mathrm{Ca}}_x{\mathrm{MnO}}_3$ $(x=0.30\mathrm{}$ and $x=0.67)$ thin films has been performed. The underdoped samples $\mathrm{}(x=0.30\mathrm{})\mathrm{}$ show a semiconductor-to-quasimetal transition, and a colossal magnetoresistance (CMR) effect around $T_C=280\mathrm{}\mathrm{K}.$ The samples with $x=0.67\mathrm{}$ 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 $x=0.30\mathrm{}$ the charge carriers are hole-type, whereas for $x=0.67\mathrm{}$ we observe electron-type carriers. The extraordinary Hall coefficient $R_A$ can be linked to the longitudinal resistivity ${\rho }_{\mathrm{xx}}$ via $R_A\propto {\rho }_{\mathrm{xx}}^{\alpha }$ with $\alpha =1.38\mathrm{}$ for $x=0.30,$ and $\alpha =0.60\mathrm{}$ for $x=\mathrm{0.67.}\mathrm{}$

• Received 8 June 2000

DOI:https://doi.org/10.1103/PhysRevB.62.11633