Magnetoresistance and Hall effect in La0.8Sr0.2MnO3

A comparative study of the longitudinal rho(xx) and transverse rho(xy) resi stivities and magnetic susceptibility chi(ac) of La0.8Sr0.2MnO3 single crys tals and ceramic samples has been conducted in a wide range of temperatures T=1.7-370 K and magnetic fields, H=0-13.6 T. It turned out that the relati on rho(xy)similar to rho(xx), which is expected to hold in the case of carr ier scattering by magnetic fluctuations, applies to the single crystals. In polycrystals, an additional H-dependent contribution to the resistivity te ntatively attributed to plane (near grain boundaries) and bulk "defects" of the magnetic sublattice has been detected. The scattering of carriers by t hese defects does not make a notable contribution to the anomalous Hall eff ect and magnetic susceptibility chi(ac). As a result, the curve of rho(xy) versus rho(xx) seems to be steeper than a linear dependence. Under the assu mption that the materials under investigation are metals with constant carr ier concentrations, the conductivity sigma=1/rho(xx) due to the critical ma gnetic scattering calculated in the molecular field approximation reproduce s the main features of experimental data, namely, the drop in the amplitude and shift of the resistivity peak near the Curie point with increasing mag netic field H and also a relatively slow change in the derivative d sigma/d H with increasing temperature in the region T less than or equal to T-C. Th e large hole concentration of about two per unit cell derived from Hall mea surements indicates that carriers of opposite signs can coexist in these ma terials. (C) 1999 American Institute of Physics. [S1063-7761(99)02308-2].