Observation of hyperfine-enhanced nuclear polarisation in CoF2 by means of neutron diffraction

By means of elastic neutron scattering the authors have observed for the first time the polarisation of the 59Co-nuclei in the hyperfine field of the ordered electronic magnetic moments through the term (b+-b-) not=0 in the structure factor. The polarisation I of the nuclear moments gives rise to a new Bragg peak in CoF2 whose intensity is proportional to I2(b+-b-)2. At very low temperatures (T<20 mK) I becomes large enough to produce a measurable (001) Bragg peak in CoF2. The results indicate that they have achieved I=0.18 corresponding to a nuclear temperature of 19 mK. The corresponding (001)-intensity was 1% of the (002) peak.