Magnetic Frustration and Anisotropy Effects in Giant Magnetic Molecule Mo_<72>Fe_<30>(Condensed Matter : Electronic Structure, Electrical, Magnetic and Optical Properties)

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A large, almost spherical magnetic molecule of Mo_<72>Fe_<30> is studied theoretically. The Fe^<3+> ions having S = 5/2 are located at the vertices of icosidodecahedron, which consists of 32 faces (20 triangles and 12 pentagons). This system is frustrated so that it has some similarity with the two-dimensional triangular antiferromagnet, but because of the pentagons it is different from the latter. The presence of pentagons leads to more degeneracy in the classical ground state, which can be lifted by fluctuations and magnetic anisotropy. In this paper we study both effects on the magnetic susceptibility and the specific heat, using mainly the Monte Carlo method. As for the anisotropy energy, it is pointed out that because of the low symmetry of the nearest-neighbor Fe-Fe bond the Dzyaloshinsky-Moriya (DM) term must be present. It is concluded from the results that the anisotropy is playing an important role in many experimental results.
社団法人日本物理学会の論文
2004-09-15