Bromine Nuclear Magnetic Resonance in Ferromagnetic CrBr3

Abstract

The nuclear magnetic resonance of ${\mathrm{Br}}^{79}$ and ${\mathrm{Br}}^{81}$ has been studied in ferromagnetic Cr${\mathrm{Br}}_3$.${\mathrm{Br}}^{79}$ resonances were observed at 53.744±0.010 and 130.64±0.10 Mc/sec, and ${\mathrm{Br}}^{81}$ resonances were observed at 55.321±0.010 and 121.61±0.10 Mc/sec in zero applied magnetic field at 1.48°K. This compares with quadrupole frequencies of 101.82 and 85.73 Mc/sec in the paramagnetic state observed for the same two isotopes. The shift in frequencies produced in the ferromagnetic state arises predominantly from the magnetic hyperfine field $H_N$ at the bromine sites. The observed resonant frequencies and their temperature dependence can be explained by assuming $\left|H_N\right|\sim 36$kOe at 0°K. Nuclear spin-lattice relaxation rates at 1.3 and 4.2°K are reported. The observed ${\mathrm{Br}}^{79}$ and ${\mathrm{Br}}^{81}$ rates are an order of magnitude faster than the rate calculated for relaxation of the nuclei by the Raman scattering of spin waves.