MAGNETIC PERCOLATION AND GIANT SPONTANEOUS HALL-EFFECT IN LA1-XCAXCOO3 LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-0.5)

We report an unprecedentedly large spontaneous Hall effect in ferromag netic La1-xCaxCoO3 (0.2 less than or equal to x less than or equal to 0.5) epitaxial films. The effect exceeds existing theoretical predicti ons for the value of the spontaneous Hall resistivity rho(xy) by sever al orders of magnitude. The Hall effect is the strongest for x=0.2, wh ich is at a doping level nearest to the ferromagnetic percolation thre shold in La1-xCaxCoO3. We suggest that the coexistence of high-and low -spin configurations in the perovskite cobaltites, together with the m agnetic percolation behavior, may be responsible for the giant Hall ef fect.