Abstract: The relationship between the high-frequency magnetic properties and surface structure of the amorphous [Co_(0.94-x)Fe_(0.06)(MnMo)_x]_(77)(SiB)_(23) alloys annealed at 400-500℃ then control-cooled was investigated using XRD,TEM and XPS techniques.The results have shown that the high-frequency losses of the present alloys ob- viously reduced after suitable treatment.A crystalline layer with ultrafine grains of γ-Co formed on the surface of the amorphous ribbons.The size of the grains is 10-20 nm.The thickness of the layer is less than 0.1 μm.The sur- face of the crystalline layer is covered with an extremely thin oxide film which is very uniform and dense with thickness of less than 30 nm,the size of grains of the oxide is less than 10 nm.These ultrafine grains and the dense oxide film effectively refine the magnetic domains and increase the resistance of the layers of the magnetic core,consequently the losses at high frequency are fairly reduced.

Key words: magnetic property, amorphous alloy, surface structure