ANOMALOUS HALL-EFFECT IN GD-DOPED LA2 3CA1/3MNO3/

Ceramic samples of composition (La1-xGdx)(2/3)Ca1/3MnO3 were prepared and used as targets to grow films onto LaAlO3 substrates by pulsed las er deposition. Comparison of the electrical resistance and thermopower , measured vs temperature and applied magnetic fields, indicates trans port dominated by positively charged small polarons in the high temper ature paramagnetic state. Nonetheless, the Hall effect, measured in 0. 5 mu m thick films of composition x = 0 and x = 0.25, has the sign tha t is normally ascribed to negatively charged free carriers. The magnit ude of the Hall coefficient decreases exponentially with increasing te mperature with an activation energy that differs from that of the resi stivity. This behavior and its anomalous negative sign are interpreted to result from face-diagonal hopping of small polarons in the Mn subl attice. (C) 1997 American Institute of Physics.