Electrical, Magnetic and Mechanical Properties of Nanocrystalline Nickel
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performance inductive magnetic recording heads[7]. These are reproduced in Table 1 which also lists the reasons for each of the property requirements. Jagielinski pointed out that conventionally processed Permalloy, Sendust and amorphous alloys currently used in recording heads will not meet new materials requirements[7]. He concluded by stating that "the future lies in multilayers and artificial structures in which properties can be engineered independently during the fabrication process." Table 1: Materials requirements for magnetic recording heads (adapted from ref. 6) Property
Reason
Large saturation magnetization High permeability at all frequencies
Large gap field Easier fabrication process High efficiency over wide frequency range
Small coercivity with low hysteresis losses
Low thermal noise
Small but nonzero uniaxial anisotropy
Control of domain structure and permeability at high frequency
Low magnetostriction (negative X,)
Low media contact noise and anisotropy control
High resistivity
Minimize eddy current losses and improve high frequency permeability
Wear resistant
Long Life
Corrosion resistant
Long Life
Good thermal and time stability
Reliability
Low forming effect
Easy and reliable manufacturing process
In the following sections we will first describe how nanoprocessed soft magnetic materials can be synthesized by electrodeposition. This will then be followed by an assessment of some of the critical materials properties required for future recording head technology. SYNTHESIS OF NANOCRYSTALLINE SOFT MAGNETS BY ELECTRODEPOSITION
There are several techniques for the synthesis of nanocrystalline materials including gas condensation, ball milling, spray conversion, spark erosion etc (for a recent review see ref. 8). Our research efforts have concentrated on electrochemical production methods including conventional DC electroplating, pulse electrodeposition, electroless plating, as well as codeposition processes to produce nanocomposite materials[9]. The major advantages of electrochemical methods over other techniques are: (1) the potentially very large number of pure metals, alloys and composite systems which can be readily electroplated as nanocrystals, (2) the low initial capital investment required to synthesize such structures and (3) the relatively minor technological barriers to be overcome in future technology transfer. Furthermore, electrodeposition processes can be tailored to either produce thin coatings or bulk deposits. Ni based alloys such as Permalloy, Hymu, Supermalloy and Mumetal have been used as soft magnetic materials for many years[10]. These alloys contain iron and other alloying 40
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elements such as Mo, Cu, and Cr in various concentrations depending on the magnetic property to be optimized. We are presently studying the synthesis of sever
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