Influence Of Cryogenic Treatment On Soft Magnetic Properties Of Fe-Ni-based Amorphous Alloy

Cryogenic treatment was conducted by immersion of the melt-spun Fe₄₀Ni₃₈B₁₉Mo₃ and Fe₄₀Ni₃₈B₁₈Mo₄ amorphous alloys in liquid nitrogen for different times. The structures and thermal stability of the as-spun and treated specimens were characterized by X-ray diffraction?XRD? and differential scanning calorimeter?DSC?. The magnetic properties of the specimens after cryogenic treatments with different times were investigated by B-H hysteresis loop tracer and vibrating sample magnetometer?VSM?. Domain structures of the as-spun and treated specimens were observed by powder pattern method.The influences of atomic structures and domain structures on the magnetic properties of amorphous alloys were discussed.The XRD results show that the atomic configurations of amorphous alloys become more disorderly due to cryogenic treatment. With the increase of the cryogenic treatment time, the free volume of amorphous alloys tends to decrease.Furthermore, the coercive forces and the saturation magnetic induction densities show a non-monotonic change with the cryogenic treatment time, which results from the comprehensive changes of short-range orders and the free volume. The soft magnetic properties of the melt-spun Fe₄₀Ni₃₈B₁₉Mo₃ amorphous alloy after the appropriate time of cryogenic treatment are improved due to cryogenic treatment. The coercive force and the saturation magnetic induction density of Fe₄₀Ni₃₈B₁₉Mo₃ amorphous alloy are improved after cryogenic treatments of 4 h,6 h, 8 h and 12 h. However, cryogenic treatment is not conducive to improving the soft magnetic properties of the melt-spun Fe₄₀Ni₃₈B₁₈Mo₄ amorphous alloy.The coercivity of Fe₄₀Ni₃₈B₁₈Mo₄ amorphous alloy becomes lager than the melt-spun state and the saturation magnetization intensity becomes smaller than the melt-spun state due to cryogenic treatment. In the melt-spun Fe₄₀Ni₃₈B₁₉Mo₃ amorphous alloy, there exist dendritic, labyrinth and star-shaped radial domains.The effect of cryogenic treatment on the magnetic domain structure is obvious.After deep cryogenic treatment, the labyrinth domains and star-shaped radial domains disappeared. The dendritic domain expands gradually with thecryogenic treatment time, and also disappears when the time of cryogenic treatment is longer than six hours. The curved band domain and ring domain appear in the melt-spun Fe₄₀Ni₃₈B₁₉Mo₃ amorphous alloy after deep cryogenic treatment and the numbers of domain increase with the increase of cryogenic time. The changes of the domain structures of the amorphous alloys are suggested to be attributed to the changes of the free volume and the atomic configuration. The changes of the soft magnetic properties origin from the changes of domain structures...