Magnetic Temperature Transducers Made from Copper Based Soft Ferrite

Soft ferrites in the CuZnTi system, having the chemical composition Cu1-x-yZnxTiyFe2O4 with 0.5£x£0.7 and 0.00£y£0.05 were investigated as a function of composition, sintering temperature and cooling speed, in order to obtain materials with different Curie temperatures, between 30 and 180 oC and very high change rate of permeability with temperature around their Curie points. Such materials are well suited to use as high sensitive magnetic temperature sensors and transducers for temperature control. Zn and Ti additions to copper ferrite change the Curie temperature in a controllable manner, thus being possible to produce ferrite material with a fine control of the Curie point at any desired temperature. Most important was the behavior of magnetic permeability with temperature around the Curie point, where it may change with about 60 %/oC by a proper choice of the cooling speed of samples from the sintering temperature to room temperature. This makes such materials extremely attractive as magnetic temperature sensors of high sensitivity. Two applications of such materials as temperature sensors, namely an ultrathermostat and an on-off switch type relay were designed. Their functionality and performances are presented and discussed.