Influence of Magnetic Interaction on Nuclear Orientation of Cobalt-60 in Rare-Earth Double Nitrates

The effect of ionic spin-spin interactions on nuclear orientation of cobalt-60 in cerous zinc nitrate has been investigated in single-crystal spherical samples cooled below 1°K by adiabatic demagnetization. An experimental demonstration is given that Ce-Co interaction is indeed the cause of the apparently anomalous alignment data. By hypothesizing the existence of a temperature-dependent internal magnetic field, exerted on cobalt ions by cerium dipoles, a simple but quantitatively satisfying description of the observed phenomena is obtained. In the theoretical calculations, measured values of $g$ factors and hfs splittings of cobalt ions in the cerium salt are used. Crystal structure information is invoked only for the purpose of a symmetry argument. The effectiveness of Ce-Zn nitrate as a paramagnetic medium for nuclear orientation experiments is pointed out.