Research On Organic Magnets Under High Pulsed Magnetic Field

With the development of computer, the computation of electronic structure for practical materials (up to one hundred atoms) has become available. On the other hand, quantum mechanics theory gives a firmly theoretical foundation for the study of ground states and excitated states of materials. Then the quantum mechanics calculation has become one of the most powerful tools in condensed matters. With the quantum mechanics theory calculation, we can not only get the properties of materials, but also simulate their behaviors under different conditions. This means that we can predict the properties of materials and design the required materials.Here we use the quantum mechanics theory to study the magnetic properties of several organic magnetic materials. Our work is to calculate the magnetic moment and the thermodynamic properties of the materials under the high pulsed magnetic field. The calculations have been done with the mathematica5.0 code.Traditional magnetic materials are metals with 3d or 4f electrons. But they can not fulfill the requirements under some conditions with the development of science and technology. So it is important to find new magnetic materials. During the last two decades, people have fabricated a lot of organic magnets or metal-organic magnets (molecular magnet). The molecular magnet can be dived into different parts corresponding to the different types of the constitutive magnetic centres: purely organic magnet, inorganic coordination complex and charge transfer salt. In this paper, we mostly study the magnetic moment and thermodynamic properties of [Mo₁₂O₃₀(μ₂-OH)₁₀H₂{Ni(H₂O)₃}₄]·14H₂O and predict the properties of two different materials under the high magnetic field. The magnetic and thermodynamic properties of the spin-1 tetrahedral"Ni4"model have been investigated in terms of the Heisenberg model by algebraic method. It is shown that the Heisenberg model provides an adequate description of the magnetization at low temperatures about 0.4K. The temperature dependence of the specific heat of this model in the vicinity of the midpoint at the rising magnetization M shows remarkable double-peak structure due to the ferromagnetic gapless and antiferromagnetic gap excitation of the spin system. The magnetization curve has four clear plateaus, and the susceptibilities exhibit typical antiferromagnetic feature, which is well consistent with experimental findings. Also we have predicted the properties of two different materials and calculation the properties of other different materials.The exchange and correlation interaction in the quantum mechanics theory are often approximated by neglecting the other interaction except the next and the next-to-next interaction. There is some difficult for the quantum mechanics theory if the number of the system is too large. The reason is that in the quantum mechanics theory we have calculated all the interactions of the system. In order to overcome this problem, the method of Monte Carlo and Green's function theory will be employed.