Nuclear spin ordering observed by neutron diffraction (invited)

Abstract

A review is given of recent neutron scattering experiments which have been carried out at milli-Kelvin temperatures to study the hyperfine-enhanced nuclear-spin ordering in the singlet electronic ground state compounds PrSn3, PrCu2, and HoVO4. Bragg peaks were observed in PrSn3 which are due solely to the nuclear spin polarization of 141Pr caused by the hyperfine field from the antiferromagnetically ordered electronic moment. The temperature dependencies of the nuclear polarization and the additional electronic polarization induced by the nuclear polarization have been measured in detail. A magnetic phase transition in PrCu2 which is believed to correspond to a simultaneous ordering of both the nuclear and electronic spin systems has been observed at 58 mK. The positions of the magnetic diffraction peaks in reciprocal space are represented by G±τ, where G is a vector of the reciprocal lattice and τ=0.24a*±0.68c*, indicating that the magnetic periodicity is incommensurate with the chemical lattice. In HoVO4 magnetic diffraction peaks due to the antiferromagnetic ordering of the nuclear spin system were observed below 4.5 mK. The observed magnetic structure and the dependence of the neutron diffraction intensities on magnetic field are consistent with the predictions of Bleaney on the basis of dipolar energy considerations.