A very large aftereffect is observed in sputtered amorphous Tb-Fe films with uniaxial anisotropy perpendicular to the film plane. In the present experiment, the film is first saturated to -Ms by a premagnetizing field Hp (<0), where Ms is the saturation magnetization. Then the applied field is suddenly changed from Hp (<0) to Ha (?0) which is close to the coercive field. With proper choice of the film composition, temperature, Ha and so on, the magnetization changes from -Ms to almost +Ms with the passage of time while Ha is kept constant. The dependences of the aftereffect on the applied field and on the temperature are shown. The domain observation by means of polar Kerr effect reveals that the aftereffect is associated with the slow dendritic growth of the magnetic domains. It is also found that the density of reversed domain nuclei depends on the premagnetizing field Hp.
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