MAGNETIC BEHAVIORS AND THEIR EFFECTS ON THE CONDUCTIVITY IN SINGLE-CRYSTAL LA2CUO4

Magnetic behaviors and their effects on the conductivity are examined in the Neel state (T(N) congruent-to 210 K) of La2CuO4 single crystals. The magnetization jump at a field-induced weak ferromagnetic (WF) transition and the critical field exhibit the same T-dependence as the sublattice moment. The magnetoresistance DELTA-R, observed at the WF transition, takes a small positive value down to approximately 110 K (T*), while for T less-than-or-similar-to T*, DELTA-R is negative and its magnitude increases drastically with lowering T. At T*, a magnetic transition is also observed; it is accompanied by a large decrease of hopping conductivity due to an enhancement of Anderson localization. It is shown that the large negative delta-R for T less-than-or-similar-to T * is due to the increase of the carrier mobility, which arises from the fac t that the enhancement of Anderson localization below T* is largely suppres sed by the spin structure change at the WF transition.