Effect of temperature on the magnetic properties of ceramic magnetic materials used for temperature transducers

Three ceramic magnetic compositions within the CuZnTi ferrite system, having the Curie temperatures centered around 60°C, 80°C and 100°C, respectively were investigated in order to determine the time-temperature stability of their main magnetic properties. Rates of changes of 33, 66 and 100 ppm/h of the maximum slopes of permeability were found for the samples aged at 60°C, 80°C and 100°C, respectively. The samples aged at temperatures higher than 200°C show a rather sudden decrease of the maximum slope of permeability, but no shift of the Curie temperature and the working point, corresponding to the temperature where the slope has the maximum value. The results are discussed in terms of the migration processes of the cations, especially Cu²⁺, from metastable positions on which they were frozen during the rapid cooling of the samples from the sintering temperature, to the more stable ones, namely the octahedral sites into the spinel lattice.