Giant spontaneous Hall effect and magnetoresistance in La1-xCaxCoO3(0.1 <=x <= 0.5)

Results of resistivity and Hall effect measurements in La1-xCaxCoO3 (0.1 le ss than or equal to x less than or equal to 0.5) epitaxial films and cerami cs an presented. The spontaneous Hall effect in La1-xCaxCoO3 (LCCO) is obse rved for ferromagnetic samples with x greater than or equal to 0.2. The Hal l effect is largest near the magnetic percolation threshold x = 0.2. For x = 0.2, the low-field slope of the Hall resistivity, rho(xy)/(mu(0)H), attai ns a large value of 2 x 10(-6) m(3)/C below the Curie temperature T-c, whic h may be applied to sensitive low-held detection. Except near the magnetic percolation threshold, the longitudinal resistivity of LCCO decreases with increasing field at all temperatures. Anomalous temperature-dependent magne toresistance occurs in the sample with x = 0.2, which may be associated wit h the spin-state transition in LCCO. (C) 1998 American Institute of Physics . [S0021-8979(98)26211-6].