⁵⁹Co NMR in an Antiferromagnetic KCoF₃ Single Crystal

Abstract

The properties of the ⁵⁹Co NMR in a single crystal of KCoF₃ were studied by a transient NMR technique at low temperatures. The observed spectrum is composed of seven distinct lines split by the nuclear-quadrupole interaction. The frequency of the central (±1⁄2↔±1⁄2) transition extrapolates to 372.7±0.05 MHz at 0 K, corresponding to the hyperfine field of 370.7±0.05 kOe. The line separations were not equal having the average value of 2.1±0.5 MHz. The hyperfine field and the quadrupole interaction agree with the calculated values based on the Co²⁺ ground state wave function. A large shift as much as 34% was observed for the nuclear g-factor, which is expected mainly from the residual orbital moment of the Co²⁺ ions. It was also found that external fields above 35 kOe along one of the c-axis make all the domains in the antiferromagnetic state to be perpendicular to the field.