The temperature dependence of the nuclear magnetic resonance (NMR) frequency of ${\mathrm{Co}}^{59}$ nuclei in single-domain particles of fcc cobalt metal has been measured in the temperature range between 4.2 and 570°K, using a conventional super-regenerative oscillator spectrometer. Two surprising results have emerged. First, the normalized fractional decrease of the resonance frequency, $\Delta \mathrm{}\left(T\right)=\frac{\left[\nu \mathrm{}\right(T)-\nu \mathrm{}(0\left)\right]}{\nu \mathrm{}\left(0\right)\mathrm{}}$, can be quite accurately fitted by the simple expression $\alpha T^{\frac{3}{2}}$ to temperatures as high as about 450°K, with $\alpha =(4.87\mathrm{}\pm 0.01)\times {10}^{-6\mathrm{}}{\left({}_{}{}^{\circ }{}_{}{}^{}\mathrm{K}\right)}^{\frac{-3\mathrm{}}{2}}$. Second, when these measurements are compared with earlier studies of the temperature dependence in walls of multidomain-Co particles, it is found that the $\Delta \mathrm{}\left(T\right)\mathrm{}$ in single-domain particles is greater than that in walls at all temperatures.

• Received 16 December 1968

DOI:https://doi.org/10.1103/PhysRev.183.559