SPIN-WAVE THEORY OF THE PHASE-TRANSITION INDUCED BY A MAGNETIC-FIELD PERPENDICULAR TO THE CUO2 PLANE IN LA2CUO4

A spin-wave theory is developed for the canting antiferromagnetism by using the Holstein-Primakoff transformation. The correction arising fr om interactions between spin waves can be obtained easily in this theo ry. The theory is applied to study the field-induced transition in La2 CuO4 when the magnetic field is perpendicular to the CuO2 plane. The t emperature dependence of the critical magnetic field predicted by our theory agrees fairly well with experiment at low temperatures. The cor rection terms are quite small at low temperatures, where the theory fi ts experiment well. This means that the simple theory, neglecting spin -wave interactions, is sufficient for practical purposes.