Effects of ultrahigh temperature on magnetic properties of core materials

An experimental study has been made of the effects of temperature on the magnetic properties of the following ferromagnetic alloys: Orthonol, 4??79 Mo Permalloy, AEM 4750, L and Z Silectron, Transformer A, Audio Transformer A, 11.7 Alfenol, 15.5 Alfenol, 3 Mo Thermenol, 7??70 Perminvar, and Supermendur. Measurements were made of the d-c and 60 cps (cycles per second) magnetic properties in the temperature range of 24r??800 C (degrees centigrade). The materials were also evaluated after several temperature cycles between 24??500 C. The results indicate that, in general, high temperature decreased the maximum induction and the residual induction from their 24 C values. For all materials tested, with the exception of Supermendur and 11.7 Alfenol, the coercive force decreased with increase in temperature. The maximum permeability increased with increasing temperature until the Curie temperature was approached, then it started to decrease. The initial permeability also increased with increasing temperature, but unlike the maximum permeability, it generally started to decrease at a greater rate and at a lower temperature. Grain-oriented materials were more affected by temperature cycling than were unoriented materials. The effects of temperature cycling on the magnetic properties generally appeared as an increase in the coercive force, a decrease in the maximum permeability, a decrease in the residual flux density, and a decrease in the squareness ratio.