MAGNETORESISTANCE AND THE SPIN-FLOP TRANSITION IN SINGLE-CRYSTAL LA2CUO4+Y

Measurements are reported of the magnetoresistance (MR) for fields up to 23 T in La2CuO4 single crystals, which order antiferromagnetically at TN 240 K, and in which the conductivity at low temperature is characterized by hopping in localized states. Using the MR, the phase diagram of the spin-flop transition, observed when the magnetic field is applied parallel to the zero-field staggered magnetization, is mapped out. Two transitions of the background Cu2+ spins are observed, which are governed by the symmetric and antisymmetric anisotropic components of the superexchange tensor. The antiferromagnetic propagation vector changes from a at zero field to c at the highest fields. This subtle change in the ordering of the Cu2+ spins is accompanied by a large enhancement of the interlayer hopping conductivity up to a factor 2. We show that the magnetoconductance is proportional to the three-dimensional staggered moment with c direction. In an appendix we discuss the possible relevance of these results to the behavior of superconducting La2-x(Sr,Ba)xCuO4. © 1990 The American Physical Society.