Anomaly in Temperature Dependence of59Co NMR Frequency in HCP Co

Abstract

The 59 Co NMR from magnetic domains in a hcp cobalt metal was studied using a single crystal by the steady-state method over a temperature range of 4.2–516 K in zero external magnetic field. The resonance frequency ν T of the central line of the quadrupole-split NMR spectrum at temperature T was measured as a function of T . ν 4.2 was determined to be 219.78±0.03 MHz in good agreement with the previous result. The reduced frequency (ν 4.2 -ν T )/ν 4.2 was compared with the reduced magnetization ( M 4.2 - M T )/ M 4.2 . Both were found to agree well below about 60 K, but to show a marked discrepancy above this temperaure, suggesting an anomaly at about 60 K in the magnetic state of cobalt metal. Below 40 K, the temperature dependence of (ν 4.2 -ν T )/ν 4.2 was analysed based on a simple spin-wave theory. The analysis yields the spin-wave stiffness constant D =337±14 meV A 2 which is much smaller than that derived from neutron scattering.