NMR FREQUENCY PULLING IN MAGNETIC SYSTEMS

Frequency pulling, the collective effect of the nuclear spin polarizat ion on the hyperfine interaction, has been observed in various ordered magnets by comparing the NMR frequencies of doped, dilute radioactive nuclei and the host nuclei. In both the antiferromagnetic insulator M n-54-(MnCl2)-Mn-55.4H(2)O and ferromagnetic cobalt metal Co-60-Co-59 t he effect is only a few %, but in the quasi-2 dimensional ferromagnet Mn-54-Mn-55(COOCH3)(2).4H(2)O the effect is quite large (similar to 10 %) because the energy gap in this system is relatively small.