Electroless deposition magnetic properties

The influence of the underlayer was demonstrated by Mirzamaani et al. [74] and by DiMilia et al. [75]. Electroless CoP was deposited from a solution yielding an intrinsically isotropic structure onto NiP that had undergone various pretreatments. When the NiP was exposed to a NaOH treatment before CoP deposition, good inplane magnetic properties resulted, but deposition on a chemically or electrochemically pre-reduced NiP surface gave unacceptable magnetics. These authors found... 

The substrate was also found to influence the properties of the electrolessly deposited vertical media CoNiMnP, CoNiReMnP, and CoNiReP. The c-axis orientation had a larger degree of perpendicular orientation for films deposited on electroless NiP than for those deposited on Cu foil, presumably because of the smaller roughness of the former substrate [43]. The double-layer (magnetically soft interface, magnetically hard bulk) properties of CoNiReP deposited on a NiMoP underlayer [57] have already been discussed. 

The structures of electroplated hard alloys have been less extensively studied than those of similar electrolessly deposited materials. Sallo and co-workers [118-120] have investigated the relationship between the structure and the magnetic properties of CoP and CoNiP electrodeposits. The structures and domain patterns were different for deposits with different ranges of coercivity. The lower-f/c materials formed lamellar structures with the easy axis of magnetization in the plane of the film. The high-Hc deposits, on the other hand, had a rod-like structure, and shape anisotropy may have contributed to the high coercivity. The platelets and rods are presumed to be isolated by a thin layer of a nonmagnetic material. 

Electroless deposition as we know it today has had many applications, e.g., in corrosion prevention [5-8], and electronics [9]. Although it yields a limited number of metals and alloys compared to electrodeposition, materials with unique properties, such as Ni-P (corrosion resistance) and Co-P (magnetic properties), are readily obtained by electroless deposition. It is in principle easier to obtain coatings of uniform thickness and composition using the electroless process, since one does not have the current density uniformity problem of electrodeposition. However, as we shall see, the practitioner of electroless deposition needs to be aware of the actions of solution additives and dissolved O2 gas on deposition kinetics, which affect deposit thickness and composition uniformity. Nevertheless, electroless deposition is experiencing increased interest in microelectronics, in part due to the need to replace expensive vacuum metallization methods with less expensive and selective deposition methods. The need to find creative deposition methods in the emerging field of nanofabrication is generating much interest in electroless deposition, at the present time more so as a useful process however, than as a subject of serious research. 

Table 10. Magnetic properties of electroless C094B5 films deposited without (a) or with (b) an applied external field (560 G), and electroless Co92Fe2Bg film deposited with an applied external field (560 G). (T. Osaka et al., 1992 [121, 122]).

Electroless deposition offers an attractive way of producing various fillers with a conductive surface or desirable magnetic properties, which can further be used in the production of composite materials with dielectric matrices for electromagnetic shielding. 

For the media preparation, 25-nm-thick CoZrNb soft magnetic film was sputtered onto Ni-P SUL and then a thick CoPtCr-SiC>2 granular recording layer. For comparison, a media with 200-nm-thick sputtered CoZrNb SUL was used. The results showed that an electroless-deposited ferromagnetic Ni-P layer (low phosphorus content), which is suitable for mass production as a SUL for a double-layered perpendicular recording media, exhibits almost the same magnetic properties and recording performances as a 200-nm-thick sputtered SUL. In addition, the spike noise which is commonly observed from SUL was not found for the media with Ni-P SUL. 

Takai M (1995) Magnetic properties of electroless-deposited NiFeB and electrodeposited NiFe alloy thin films. lEICE Trans Electron E78-C 1530-1535... 

Osaka T et al (1994) Soft magnetic properties of electroless-deposited CoFeB films. J Magn Soc Jpn 18(S1) 183-186... 

Sugiyama A (2005) Magnetic microstructure and noise property of electrolessly deposited CoNiFeB soft magnetic underlayer. IEEE Trans Magn 41 3163-3165... 

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