Defect level evaluation for magnetic ceramics

The researchers from Tomsk Polytechnic University proposed a novel method for evaluating defect level of ferrimagnetic ceramics. Such ceramics is widely used as magnetic materials in microwave radio engineering and computer technology since it combines high magnetization and semiconductor or dielectric properties. Minor defects such as nonmagnetic impurities that occur in ceramics fabrication can cause device failure. The study results were published in the Journal of Magnetism and Magnetic Materials (IF 2.63; Q2).

Ferrite ceramics samples Photo: Ferrite ceramics samples

The study was carried out on the LiTiZn ferrite ceramics. The temperature dependences of initial permeability were analyzed for samples sintered in laboratory conditions and for the ferrite industrial products.

SRF Andrey Malyshev from the Research Laboratory for Electronics, Semiconductors and Dielectrics says: ‘In the production, ferrite ceramics is traditionally tested by investigating a small set of electromagnetic and physical parameters of a sample at room temperature and comparing data obtained with standard values for this material. However, these parameters are not studied at a wide range of temperatures including the transition point to the paramagnetic state.’

TPU scientists proposed a method based on temperature dependence analysis of initial permeability of ferrite ceramics. It is a structurally sensitive value which characterizes magnetic properties of a substance.

‘At first, we experimentally measure temperature dependences of initial magnetic permeability for a particular sample in a temperature cell, i.e. how magnetic properties depend on different temperatures.  Then using mathematical tools, i.e. a phenomenological expression presented in the article which makes it possible to process experimental data and obtain two parameters affecting the defect level. They are associated with elastic stresses in materials and their ratio is the parameter of the defect level. This is the peculiarity of the method: we do not identify particular defects in a sample, we demonstrate how their aggregate deprave its magnetic properties,’ - explains the scientist.

The proposed method allows controlling integral defect level of soft ferrite products and has high sensitivity compared to typical X-ray methods. 

‘The method is sufficiently fast and effective in application, so in the long term it can be used in production when assessing the quality of products obtained from magnetic ceramics,’ notes Andrey Malyshev.

The study is backed in the framework of the Nauka program of the Ministry of Education and Science of Russia. The computation of experimental data was carried out in the framework of the grant of the TPU Competitiveness Enhancement Program.