Magnetic Properties of KMnF3. III. Nuclear and Electron Spin Resonance

Direct NMR experiments on ${\mathrm{Mn}}^{55}$ nuclei in KMn${\mathrm{F}}_3$ have confirmed that KMn${\mathrm{F}}_3$ is a weak ferromagnet. The strong field and temperature dependence of the NMR frequency is a result of the intermixing of the electron and nuclear excitation spectra. A four-sublattice model for the electronic magnetization has been used to analyze the angular dependence of the NMR frequency. This four-sublattice model employs two canting fields, an "overt" canting field $H_2$ and a "hidden" canting field $H_5$. The overt canting field introduces a term into the expression for the AFR frequency that is linear in the applied dc magnetic field; this linear dependence is verified by experiment. With $H_2=310\mathrm{}\pm 20$ Oe and $H_5=200\mathrm{}\pm 30$ Oe. the hidden canting angle between ${\mathrm{M}}_1$ and ${\mathrm{M}}_3$ is approximately 100°. The resonance frequency in the nuclear hyperfine field was found to be 676±3 Mc/sec; when compared with the paramagnetic resonance results of Ogawa, this would suggest a 1.6% zero-point spin-wave reduction in $〈S〉$.