Exploration of new magnetic materials by controlling nanostructures

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Spinel-type magnetic materials with ordered array of two types of rectangular nanorods, characterized as chessboard-type (CB-type) nanodomain structures, have been explored by changing the isothermal annealing time at 648 K. We successfully synthesized magnetic materialswith highly organized CB-type nanodomains developed through the isothermal annealing treatment from 10 to 730 hours. By optimizing synthesized conditions, it was revealed that the CB-type nanodomain structures with ~50 nm2in size are formed, consisting of two distinct nanorods with ferromagnetic CoFe_<1.4>MnO_4with the cubic structure and paramagnetic CoFe_<0.4>Mn_2O_4with the orthorhombic structure. We demonstrated that the formation of characteristic CB-type nanodomains resulted in the development of magnetic properties. In addition, magnetic materials without rare-metal elements were successfully synthesized by partial substitution of Cu for Co in Co(Fe,Mn)_2O_4