High frequency initial permeability of nanocrystalline NiMnCu ferrites

The structural and magnetic properties of nanocrystalline Ni_0.50-xMn_xCu_0.50Fe₂O₄ powders were synthesized by combustion technique. Toroid and pellet-shaped samples prepared from these powders were sintered at various temperatures (1150-1300°C). The XRD patterns of various compositions showed well defined single crystalline phase and formation of spinel structure. It is also found that the lattice constant increases with increasing Mn content, obeying Vegard´s law. The optical micrographs of various compositions showed that due to increase of small amount of Mn average grain size is very large. When Mn was substituted the real part of complex permeability enhanced from 30 to 116 depending on chemical composition and sintering temperature. The DC magnetization shows that at room temperature all samples are in ferrimagnetic state.