NMR frequency pulling in magnetic systems

Frequency pulling, the collective effect of the nuclear spin polarization 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 insulator54Mn-55MnCl2.4H2O and ferromagnetic cobalt metal60Co−59Co the effect is only a few %, but in the quasi-2 dimensional ferromagnet54Mn-55Mn(COOCH3)2.4H2O the effect is quite large (≈10%) because the magnon energy gap in this system is relatively small.