Pulsed Electrodeposition of Nanocrystalline CoNiFe Soft Magnetic Thin Films

Abstract

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...

In-depth component distribution in electrodeposited alloys and multilayers

“…This is why TEM was applied for Ni-Co-Fe samples deposited with analogous conditions than those studied with SNMS reverse depth profiling. In former reports describing a TEM study of Ni-Co-Fe samples [39,41,[44][45][46], the near-substrate composition gradient shownin the previous chapter was not mentioned.…”

The annealing temperature dependences of microstructures and magnetic properties in electro-chemical deposited CoNiFe thin films

“…Therefore, a small stimulation can induce the stabilization of either structure. It can be assumed that the thermal treatment in Fe which depend on the annealing condition determine the crystal structure of CoNiFe, because Fe itself can have both bcc and fcc structure [17]. …”

“…These parameters can be optimized by working, processing condition and post deposition treatment of material to achieve desired magnetic properties [4]. The important parameters for achieving such excellent properties is crystal structure which can be obtained by the compositional region between fcc and bcc structures [1][2][3][4][5].…”

Thermal Synthesis of Nanocrystalline (Co<SUB>x</SUB>Ni<SUB>1-x</SUB>)<SUB>y</SUB>Fe<SUB>1-y</SUB> KOVAR Alloy through Gaseous Reduction of Mixed Oxides

“…NiCoFe ternary alloys, rich in Co, have been reported with higher saturation magnetic flux density and lower coercivity than Permalloy (Ni 80 Fe 20 ), which can be used to develop more sensitive thin film magnetic heads for high-density recording. [6][7][8][9][10][11][12][13][14][15][16][17][18][19] Also, NiCoFe ternary alloys, rich in Fe, have also been noted for their low thermal expansion property. Commercial applications of these alloys include microwave guides, spacecraft optics, laser housings, and printed wired boards.…”