Hyperfine induced magnetic order in Pr: neutron diffraction at mK temperatures

The magnetic reflections of a single crystal of pure Pr were investigated with elastic neutron scattering in the temperature range down to 8 mK. A double peak structure was found, consisting of a narrow antiferromagnetic satellite with incommensurable wave vector and a broad peak of presumably quasielastic origin, as seen in previous measurements at higher temperatures. The saturation of the magnetic moment is almost reached at the lowest temperatures and approaches the theoretical expected value of 0.6 μB. Below a temperature of T = 40 mK the magnetic moment tunes away from the b-axis towards the a-axis of the crystal. Measurements in an external magnetic field indicate 3 domains. A magnetic field along the a-axis bigger than 500 mT destroys the magnetic order