Antiferromagnetic resonance in the cubic perovskite KNiF3

Low-temperature high-magnetic-field far-infrared spectroscopy and electron- spin-resonance measurements have been performed on single crystals of the c ubic perovskite KNiF3. We found the absorption at 48.7 +/-0.3 cm(-1) observ ed by Richards [P. L. Richards, J. Appl. Phys. 34, 1237 (1963)] that was at tributed to antiferromagnetic resonance (AFMR) is not magnetic in origin. I nstead, a different absorption is well fit by a theory of AFMR with uniaxia l anisotropy. Analysis yields an anisotropy energy of 8.7x10(-3) cm(-1). Th e ratio between the anisotropy field and the exchange field is 2.3x10(-5). Thus, KNiF3 is an excellent example of a Heisenberg antiferromagnet. [S0163 -1829(99)00209-X].