Thermodynamic Studies on Magnetic Properties of Nano-Scaled Magnets

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Nano-scaled Magnets have been attracting much attention because of not only application such as a new magnetic memory but also academic aspects such as superparamagnetism, magnetic quantum tunneling, and so on. There are two strategies for development of nano-scaled magnets : top-down type and bottom-up type. In this research, I have investigated specific magnetic properties of bottom-up types of the single-molecule magnet [Mn_<12>O_<12>(O_2CPh) _<16>(H_2O)_4] and the single-chain magnet [Mn(saltmen)] _2[Ni(pao)_2(py)_2](ClO_4)_2 and a top-down type of Ni(OH)_2 monolayered nanocluster (Ni-MNC) in amorphous SiO_2.It was revealed by the magnetic-field dependence of the heat capacity of the [Mn_<12>O_<12>(O_2CPh)_<16>(H_2O)_4] crystal that the crystal has a magnetic-field-direction-dependence for the heat capacity and that the heat capacity data can be accounted for well by the spin Hamiltonian for an S=10 spin system with a uniaxial anisotropy. The magnetic-field dependence of the heat capacity of the [Mn(saltmen)]_2[Ni(pao)_2(py)_2](ClO_4)_2 crystal indicated the nature of a one-dimensional antiferromagnet. It was suggested by the magnetic-field dependence of the heat capacity of the Ni-MNC that ferromagnetic interactions exist in the Ni-MNC and among the Ni-MNCs. It was concluded by the estimated magnetic entropy that a broad magnetic thermal anomaly is due to the magnetic ordering of the Ni^<2+> cations with S=1.