An effective held theory that describes the low-frequency spin dynamics in
the low-temperature orthorhombic phase of La2CuO4 is derived. The main feat
ures of the inherent covert weak ferromagnetism are thus accounted for in a
straightforward manner but some of the finer theoretical predictions would
require further experimental investigation. In particular, theory predicts
the occurrence of magnetic stripes in undoped La2CuO4 which mediate the ob
served weak-ferromagnetic transition. (C) 2001 Elsevier Science B.V. All ri
ghts reserved.