The NMR of 53Cr nuclei has been observed in ferromagnetic CdCr2Se4, CdCr2S4, and HgCr 2Se4 at 4.2°K using spin-echo and cw techniques. The spectra are complex with a principal triplet and have been analyzed considering coaxial anisotropic hyperfine and electric quadrupole fields of comparable magnitude to be acting on the chromium nuclei in randomly oriented domains. An excellent fit has been obtained between the calculated spectrum and spin-echo data. For CdCr2Se4, CdCr2S4, and HgCr2Se4, the separation between the outer components of the triplet is 1.76, 1.90, and 1.96 MHz, the isotropic part of the hyperfine field is -182.6, -191.0, and -178.3 kOe and the anisotropic component of the hyperfine field is +2.33, +2.07, and +2.3 kOe, respectively. The signs of the hyperfine field components indicate their direction with respect to the magnetization and were determined by measuring the frequency shift with applied magnetic field. The NMR of 77Se nuclei has also been observed in HgCr2Se4 and CdCr2Se4 at 4.2°K. The spectra are consistent with the model of randomly oriented domains and exhibit a strongly anisotropic hyperfine field. The origin of the spectra and the sign of the hyperfine field components were determined by measuring the frequency variation of the spectra with applied magnetic field. © 1968 The American Institute of Physics.
