Influence of annealing temperature on the magnetic and magnetoelastic properties in Fe–Co–B metallic glasses

The magnetic and magnetoelastic properties of strip-shaped samples of Fe62Co23B15 and Fe68Co17B15 amorphous alloys have been investigated after annealing in vacuum for 1 h in the temperature range 100–450 °C. The coercivity of these samples increases from a value of 120 A/m to values around 0.8–1 kA/m after annealing above 400 °C. Magnetomechanical coupling coefficient decreased from about 0.22 (for the Fe62 sample) – 0.25 (for the Fe68 sample) in as-quenched state to less than 0.10 after annealing at 400 °C. The moduli of elasticity, measured at magnetic saturation of the samples, were also changing from values in the as-quenched state of 162 GPa (for both the Fe62 and Fe68 sample) to 210 GPa after annealing up to 400 °C. This high value of the Young’s modulus is close to the one of crystalline Fe. These properties are explained in terms of the structural changes occurring in the alloys under the heat treatments. Stress relief and structural relaxation merge with the starting of the crystallization process and a magnetic hardening of the as-quenched properties is obtained upon annealing.