Magnetism of 1D quantum ferrimagnets, A3Cu3(PO4)4 with A=Ca, Sr

Neutron and high field magnetization measurements are reported for one-dimensional (1D) quantum ferrimagnets, A3Cu3(PO4)4 with A=Ca, Sr in which the metal network is characterized by intertwining double chains of Cu(II) ions. High field magnetization up to 40 T at 4.2 K shows a clear signature of 1D ferrimagnets, i.e., a characteristic intermediate quantum state with a so-called 1/3 magnetization plateau. Neutron diffraction on powder samples of Sr3Cu3(PO4)4 at 70 mK in the magnetically ordered state reveals weak magnetic peaks. The fact that the intensity of the magnetic peaks are very weak, compared with those of the nuclear peaks, suggests that the quantum nature of the spins to essential for the ordering process of the system with discrete quantum energy levels. (author)