This would mean that the sintering temperature leads to a less ferromagnetic structure, ie the Ni 2+ ions concentration is lower leading a lower saturation moment when the sintering temperature is increased.

Behnam Farid

I think when sintering temperature increases in microstructure of ferrite to form some fault and also because zinc has high steam pressure so it is evaporated at high sintering temperature.

Behnam Farid

Lattice parameter does depends on temperature....Exchange coupling between Ni2+ ions also depends on lattice parameter... Can you confirm the same that samples with different temperatures have same crystal structure and lattice parameter?

Thank you much Gokaran Shukla. I would like to let you know that the lattice parameter initially decreases at 1050C and then increases at 1100C and finally decreases as the sintering temperature.

Dear Md D Rahaman, as you see, a lot of speculation is possible. I don't think anyone can provide a well-founded answer to your question (unless there was something obvious and known to people having worked on exactly your material).

Lattice constant might be one thing to look into (and the reason for its variation), chemical composition, cation distribution (which ions sit with what probability in which kind of site) and next grain size, density of antiphase boundaries etc... There are lots of parameters which may affect the details of the magnetic behavior you observe!

Dear Rahaman,

What about crystal structure? They remains the same? In my opinion, there should be a a huge distortion and structure must change. Is it possible for you to plot saturation magnetization as a function of lattice parameter?

Also, Professor Kai has a very valid point about cations distribution.. Is it possible for you to get the information about percentage of Ni+2/Ni+3 distributions into different void like tertrahdra and octahedra?

Dear Mr. Md D Rahaman , as I understand from your composition that you have Cu in your sample which act as a fluxing material. The melting point of Cu ferrite is around 1100C (please check). Your sintering temperature starts at 1050C and holding time 5 hours (which is quite high). I am not sure whether you looked at the microstructure. If I am not wrong, you would see some white glassy patches around the grain boundary in contrast to the grains which doesn't have spinel structure and might have zero or low magnetization. This phase would reduce your magnetization. When you increase the temperature more than 1100C the softening creeping towards the core grain which would create a distortion in the lattice. You see after 1100C your lattice parameter decreases. Another effect of Cu in your composition is, as Cu works as fluxing material it would give rise to the grain growth at a much faster pace. You need to remember that your holding time is too long when you are working with Cu in your composition. When your grain size is within few microns the pores might diffuse into the grain boundary and that is intergranular porosity. But when the grain size would increase at a much faster pace the diffusion of the pores cannot be completed to reach to the grain boundary and you have intragranualar porosity. The intragranular pores are severely deleterious for exchange coupling since they act as pinning of magnetic moment. This also reduces the magnetization. And the third point you might look into is the cation distribution. Your composition is a mixed ferrite of Ni-Cu-Zn ferrite. While Ni and Cu are inverse spinel the Zn ferrite is normal spinel. Zn occupies mainly in the tetrahedral site while Ni and Cu occupy octahedral site. You might check from the Curie temperature that whether your Curie temperature is changing. If it changes then your site occupancy also changes and in that case your exchange interaction between the ferric ions are decoupled. You might check the site occupancy of your sample using Mossbauer spectroscopy too.

Dear Dr. Raman

We found that one of the reasons for this is evaporation of zinc from the ferrite. As you go on increasing the temperature more and more zinc evaporates leaving behind Ni and Cu. It is the reason why we have to sinter these ferrites in closed atmosphere with suitable powder beds.

Can you write chemical composition (formula) of your ferrites?

Dear Professor Rahshree B Jotania

Thank you much. The chemical composition of our sample is Ni0.25Cu0.13Zn0.62Fe2O4. Best wishes for you.

Dear Dr. Rahaman

Sat. Mag. is primarily dependent on superexchange interactions led by Fe3+ ions on the crystallographic sites. As temp. Increase, Fe3+ ions are converted to Fe2+ ions leading to decrease in sup. int. Thus sat. Magn. decreases. This reduced Fe3+ ions decreases anisotropy and ferromagnetic resonance. Further Fe2+ are easily polarization than Fe3+ ions, complex permittivity is also greatly affected while complex peremeability diluted