Properties and stability of ferrite materials for magnetic temperature transducers

Magnetic materials in the CuZnTi ferrite system with the chemical composition Cu1 − xZnxTiyFe2 − yO4, with 0.5 ⩽ x ⩽ 0.62 and 0 ⩽ y ⩽ 0.05 were investigated as a function of sintering temperature and time and cooling speed in order to see the influence of these factors upon the Curie temperature and the permeability behaviour around the Curie point. The quality of the magnetic temperature transducers made from such materials is directly connected with the value of the slope of the μ(T) curve. The higher the slope the more sensitive will be the transducer. Slopes as high as 50% °C−1 were obtained by a proper cooling of the samples, this value being the highest reported so far for such materials. The results are discussed in terms of the ionic distribution of the Cu, Zn and Ti ions over the tetrahedral and octahedral sites of the spinel lattice. The materials proved to be stable in time if the temperature does not exceed 200°C, but higher temperatures may induce irreversible change in the material structure due to cation migration and electron transfer from copper ions to iron ions.