Survey of magnetic materials

There are four different classes of hard magnetic materials  

Crystal structure of (a) ReC 3, and (b) Na W03 (central large circle, Na+ of fractional site occupancy). 

1960s Magnetic materials of transition metals oxides  

The alnicos are a very important group of permanent magnetic alloys, which are used in a wide range of applications. They are essentially heat-treated alloys of variable Fe-Co-Ni-Al-Cu composition  

The alnicos are polycrystalline solids, in which very complex structural disorder generally occurs, due to the wide variety of deviations from periodicity that may be present. Physical disorder corresponds to the displacement of atoms, and/or the presence of amorphous regions and non-uniform crystallite sizes, while chemical disorder corresponds to site occupation by impurity atoms, and/or the presence of vacancies accompanied by variable valence states of 

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