FIELD-DEPENDENT MAGNETIC PHASES IN LA2CUO4 AT ZERO TEMPERATURE

The magnetic ordering in La2CuO4 is significantly affected by the existence of antisymmetric Dzyaloshinsky-Moriya interactions. We use an effective classical spin Hamiltonian to obtain the full phase diagram at zero temperature, with a magnetic field oriented along an arbitrary direction in the orthorhombic b-c plane. We show that the various transition fields are sensitive functions of the input anisotropies. Using the measured transition fields [Thio et al., Phys. Rev. B 38, 905 (1988); 41, 231 (1990)], we find that the anisotropy in the intralayer interaction is 3.4+/-0.6 meV and the interlayer interaction is 1.75+/-0.2 meV. We predict the entire magnetic phase diagram for fields in the b-c plane, including a critical end point, when the magnetic field is applied at an angle of 26.3-degrees with the c axis. We also discuss the qualitative changes expected in the phase diagram if the value of the antisymmetric exchange increases.