Abstract
The samples of nano-crystalline CoLa
x
Fe
2−
x
O
4
were prepared by ceramic method. The results show the formation of cubic inverse spinel phase for all CoLa
x
Fe
2−
x
O
4
samples in addition to impurity phase formation of LaFeO
3
for high La content samples
.
The crystallite sizes for all samples are almost 30 nm. The dielectric measurements show that the presence of La enhances the values of dielectric constant at high temperature, demonstrating Debye relaxation. The DC electric resistivity decreases with La content, suggesting that the conduction phenomenon in these samples is due to hopping of charge carriers. The positron annihilation spectroscopy shows that the large size defects decrease with La for low content samples. However, at higher La content (
x
= 0.25), the agglomeration of the defects is the dominant process. The CoLa
0.25
Fe
1.75
O
4
sample shows a different type of defect from other samples. The high electrical resistivity and low tan
δ
recommend that these samples can be used in power applications that require negligible eddy currents.