Magnetic ordering induced by hyperfine interactions in the terbium and holmium garnets

Neutron diffraction measurements have been performed at temperatures down to 0.04 K in order to check the expected temperature dependence of the spontaneous electronic magnetization below 0.24 K for TbGaG and 0.15 K for HoGaG. The particular behaviour of the magnetic polarizations due to the onset of a coupled nuclear-electronic transition, is well observed. (Auth.)