Ultrasound velocities and magnetomechanical coupling in Fe Co-Ni-Zr-Cu-Nb-B alloy strips after heat treatment

The magnetic field and beat-treatment dependences of the ultrasound velocities at constant magnetic field (CH) and at constant magnetic induction (cB) and magnetomechanical coupling were investigated in Fe62.5Co6Ni7.5Zr6Cu1Nb2B15 alloy strips in an as-quenched state and after annealing above the Curie temperature. After annealing above 350oC (up to 390oC) the magnetomechanical coupling coefficient (k) was three times higher than that for asquenched state (0.10-012), i.e. k = 0.32-0.37. The minimum values of the cH (= 3.6 km/s) were observed after annealing in the temperature range from 350 to 390oC at 75-100 A/m. There are equal or somewhat higher values of bias field for the minimum of the cH than in some other iron-rich amorphous alloys. Effect de was very small for as-quenched samples. When the samples reached the magnetic saturation, the domain structure vanished and then the Hooke's law was valid, i.e. EH = EB = E, where E was then material constant, known as Young's modulus and then the ultrasound velocities are also material constant.