Thermodynamic Studies on Magnetic Properties of Nano-Scaled Magnets

纳米磁性材料不仅具有新型磁存储等应用价值，而且在超顺磁性、磁量子隧穿等方面也具有重要的学术价值。纳米磁体的发展有两种策略：自上而下型和自下而上型。在本研究中，我研究了自下而上类型的单分子磁体[Mn_&lt；12&gt；O_&lt；12&gt；(O_2CPh)__&lt；16&gt；(H_2O)_4]和单链磁铁[Ni(PAO)_2(Py)_2](ClO_4)_2和非晶态SiO_2中自上而下的Ni(OH)_2单层纳米团簇(Ni-MNC)。(H_2O)_4]晶体的热容与磁场方向有关，对于具有单轴各向异性的S=10自旋系统，热容数据可以用自旋哈密顿量很好地解释。[Mn(Saltman)]_2[Ni(PaO)_2(Py)_2](ClO_4)_2晶体的热容与磁场的关系表明了一维反铁磁体的性质。Ni-MNC的热容与磁场的关系表明，在Ni-MNC内部和Ni-MNC之间存在铁磁相互作用。由估算的磁熵得出结论：当S=1时，Ni^&lt；2+&gt；阳离子的磁性有序是导致宽磁热反常的原因。

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.