AFMR AND MAGNETIC-ANISOTROPY IN Y1-XLUXFEO3 ORTHOFERRITES

We have investigated the AFMR modes nu(1,2)(T) in Y1-xLuxFeO3 single c rystals (0 < x < 1) in the frequency range nu = 5-30 cm(-1) at T = 4.2 -600 K. A linear dependence of nu(1,2)(2) versus x, proportional to th e magnetic anisotropy constants K-ac and K-ab in the ac- and ab-planes , was revealed. We have observed the qualitative change in the tempera ture behaviour of nu(1)(T) and K-ac(T) on going from YFeO3 to LuFeO3. This change is considered to be due to the variation between the contr ibutions to K-ac from the single-ion anisotropy, anisotropic exchange and magnetodipole interaction.