Magnetic properties of HITPERM-type alloys at high temperature

(Fe,Co)- Zr,Hf)-Cu-B (HITPERM-type) alloys with variable Hf, Zr and Co content were isothermally crystallised at 500-650 degrees C for 1 h, and the optimum nanocrystallisation temperature was selected on the basis of the minimum coercive field at room temperature. The quasistatic hysteresis loops were measured at temperature from 20 to 650 degrees C. Subsequently, the optimally annealed alloys were subjected to long-term annealing at 500, 550 and 600 degrees C. Working temperature of 600 degrees C is too high for the investigated alloys to maintain stable magnetic properties. Temperature of 550 or 500 degrees C permits the material to be magnetically stable for a long period. The magnetic hysteresis loops recorded for the nanocrystalline alloys, where Fe:Co ratio is close to 1 and refractory metals content is 7 at.%, prove that coercive field increases slightly with temperature, but remains in the range of 20-40 A/m (depending on the alloy composition) from 20 to 550 degrees C. This proves that the investigated alloys, after optimisation of chemical composition, may be suitable for high temperature use. (c) 2006 Elsevier B.V. All rights reserved.