A pulsed electrodeposition method was applied to the preparation of soft magnetic CoNiFe films in the compositional region corresponding to the phase boundary between face-centered cubic ͑fcc͒ and body-centered cubic ͑bcc͒ structures. Crystalline grain size was found to be almost the same, smaller than 10 nm, and independent of the duty cycle which is the ratio of the pulse-on time to the pulse-on plus pulse-off period. Depending on the operating conditions, the ratio of bcc to fcc varied. Current efficiency decreased with decreasing duty cycle and pulse current density. The intensity ratio of bcc͑110͒ to fcc͑111͒ X-ray diffraction peaks showed a maximum at the operating conditions in which the transition from kinetic to mass-transfer controlled deposition occurred with only a slight increase of Fe content ͑approximately 1 atom %͒. Magnetic properties were suggested to be controllable by adjusting the bcc-fcc ratio using pulsed electrodeposition.As a candidate for the head core material meeting the recent requirement for an increased magnetic recording density, 1 an electrodeposited CoNiFe alloy system, which possesses a very high saturation magnetic flux density (B s ) and a low coercivity (H c ) has been attracting much attention since our development of the electrodeposited soft magnetic Co 65 Ni 12 Fe 23 film with B s ϭ 2.1 T and H c ϭ 1.2 Oe. 2,3 The desirable properties for magnetic recording head 4 have been achieved by avoiding the inclusion of sulfur in the CoNiFe film by using a plating bath without sulfur-containing additives ͑SCAs͒ such as saccharin and thiourea. We found that a very small amount of included sulfur affects H c and magnetostriction drastically. 2,3 One of the important attributes for achieving such excellent properties is a fine grain size, which can be obtained in the compositional region corresponding to the phase boundary between face-centered cubic ͑fcc͒ and body-centered cubic ͑bcc͒ structures. 2-4 Therefore, controlling both the crystalline structure and the grain size is important to obtain desired properties.In general, pulsed electrodeposition is a common method for controlling the composition of the film as discussed in the previous papers for NiFe [5][6][7][8] In addition, pulsed electrodeposition is a feasible method for preparing nanocrystalline films. 10-12 For electrodeposited CoNiFe soft magnetic films, however, our recent investigation yielded an average grain size of approximately 10 nm by bringing the composition to the fcc-bcc mixed crystal region. 3,13 Moreover, results of dc electrodeposition suggested that the grain size of the film could be regulated not only by the composition but also by the hydrogen evolution taking place during the CoNiFe deposition, because the absence of SCAs in the bath is expected to result in the enhancement of the effect of hydrogen evolution. 14 In the present study, we apply the pulsed electrodeposition method to the preparation of the CoNiFe film in the compositional region of the fcc-bcc mixed phase and investigate the effect of op...
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