Magnetic anisotropy in molecule-based magnets

The goal of this paper is to introduce the dimension 'magnetic anisotropy' in the field of molecule-based magnets. For that, we have focused on two aspects, namely the design of a hard magnet through the incorporation of magnetically anisotropic spin carriers, and the determination of the magnetic phase diagrams of two strongly anisotropic ferromagnets. The hard magnet contains three kinds of spin carriers, Co-II and Cu-II ions as well as radical cations. It structure is very peculiar; it consists of two perpendicular honeycomb-like networks which interpenetrate in such a way that each hexagon belonging to one of the networks is interlocked with a hexagon belonging to the perpendicular network. The coercive field depends on the grain size. It can be as large as 25 kOe at 5 K. The two strongly anisotropic ferromagnets are cyano-bridged (MnMoIII)-Mo-II compounds synthesized from the [Mo-III(CN)(7)](4-) precursor, Mo-III has a low-spin configuration, with a local spin S-Mo = 1/2, and a strongly anisotropic g tensor. One of the compounds, Mn-2(H2O)(5)Mo(CN)(7) . 4H(2)O, has a three-dimensional structure. The other one, K2Mn3(H2O)(6)[Mo(CN)(7)](2) . 6H(2)O, has a two-dimensional structure. For both compounds, we have succeeded to grow well-shaped single crystals suitable for magnetic anisotropy measurements, and we have investigated the magnetic properties as follows: first, we have determined the magnetic axes by looking for the extremes of the magnetization in the three crystallographic planes, ab, be, and ac. Then, we have measured the temperature and field dependencies of the magnetization in the DC mode along the three magnetic axes. These measurements have revealed the existence of several magnetically ordered phases for the three-dimensional compound, and of field-induced spin reorientations for both compounds. For the very first time in the field of molecular magnetism, we believe we have been able to determine the magnetic phase diagrams.