Nuclear magnetic resonance in RbMnF3

The 19 F, 85 Rb and 87 Rb nuclear magnetic resonances observed at room temperature in single crystals of RbMnF 3 are described. The hyperfine interaction of a fluorine nucleus with one of its nearest-neighbour Mn 2+ ions has axial symmetry, the principal values being A || = (21.49 ± 0.90) × 10 -4 cm -1 , and A ⊥ = (12.77 ± 0.55) × 10 -4 cm -1 . The part of this interaction which is not due to classical dipole effects has been interpreted in terms of the fraction of unpaired spin in the F - 2s orbital ( f 2s = (0 50 ± 0.02)%), and the F - 2p orbital (( f σ - f π ) 2p = (0.33 ± 0 18)%). The rubidium nuclear magnetic resonance indicates a negative spin density at the rubidium nucleus, and can be interpreted in terms of the fraction of unpaired spin in a Rb + 4s orbital ( f 4s = -0.0040%). A measurement of the molar magnetic susceptibility of RbMnF 3 at 298 °K gave the value χ M = (10 40 ± 0 35) × 10 -3 cm 3 mole -1 , which is approximately 17% greater than the value previously reported by McGuire. The values of the nearest-neighbour exchange integrals (defined by H 12 = J S 1 . · S 2 ) deduced from room temperature magnetic susceptibility measurements are J (RbMnF 3 ) = (6 7 ± 0.7) °K and J (KMnF 3 ) = (7.1 ± 0.5) °K.