NMR study of the3dferromagnetic metals: Critical region and paramagnetic phase

Abstract

The ferromagnetic transition metals iron, nickel, and cobalt have been investigated by nuclear magnetic resonance up to the critical region and, in the case of nickel and cobalt, in the paramagnetic phase. The measurements include the zero-field resonant frequency, spin-spin relaxation rate, and spin-lattice relaxation rate in the ferromagnetic phase, and the Knight shift and spin-lattice relaxation rate in the paramagnetic phase. The data yield values of the static critical exponent ($\ensuremath{\beta}$) for the spontaneous magnetization and the dynamic exponent ($z$) for spin fluctuations near the critical points of all three ferromagnetic metals. Paramagnetic-phase data for nickel and cobalt yield the $d$-spin hyperfine coupling and the orbital Knight shift and susceptibility contributions. Magnetic equation-of-state parameters are derived for nickel and cobalt. Noncritical spin-spin relaxation rates in the ferromagnetic phase are attributed mainly to Suhl-Nakamura interactions, but in bulk metal samples the rates exhibit a striking and unexplained maximum between room temperature and the critical point.