Permalloy , magnetic properties

Initial experiments showed that the PMDA/ODA material can be successfully cured by a ot plate bake at 280° C for 3 hours. Electrical.Loss tangent data showed that imidization was complete under these conditions. As noted before,the passivation process for bubble devices had to be optimized by using a lower temperature ( to preserve the magnetic properties of the permalloy structures).without losing the electrical insulation characteristics of the final polyimide. IR technique was used as the method of detecting complete cure. A Perkin Elmer 283 spectrometer was used for the IR analyses routinely,and in a few cases the results were checked with a Digilab FTIR instrument.Routine resolutions were 2cm with the Perkin Elmer instrument. Jh s g-dies of imide formation by IR is a well known technique ... 

In the Ni-Fe system at room temperature, the a phase extends from 0 to 7% Ni, then a. Fy mixtures from 7 to 50% Ni, and the y phase from 50 to 100% Ni. y-Phase alloys in the Ni-Fe system, known as Permalloys, exhibit a wide variety of magnetic properties, which may be controlled precisely by means of well-established technologies. Initial permeabilities up to 10 in an extremely wide temperature range, as well as coercive fields between 0.16 and 800 A/m, can be obtained (Chin Wemick, 1980). Induced anisotropy of 65-85% Ni alloys can be drastically varied by field annealing and mechanical deformation (slip-induced anisotropy) an order-disorder transformation occurs for Ni3Fe finally, preferential orientation can be induced in 50%Ni-50%Fe. 

Yi] Yi, J.B., Li, X.P., Ding, J., Sect, H.L., Study of the Grain Size, Particle Size and Roughness of Substrate in Relation to the Magnetic Properties of Electroplated Permalloy , J. Alloys... 

The deposition of Fe-Ni alloys is of industrial interest because these materials find applications in electronic devices (e.g. PC hard disk). The most popular alloys are Permalloy (soft magnetic properties) and Invar (veiy low thermal expansion). The magnetic and mechanical properties of Fe-Ni alloy can be designed by nanostructuring. Natter and Hempelmann (2003) used an electrolyte containing 40g/l NiS04, 20g/l (NH lCl, 20g/l Na citrate, 5g/l citric acid, lg/1 saccharin, 45 g/1 boric acid and a variable content of iron (II) ammonium sulfate. The pulse parameters used were t 2 ms, 48 ms and 250mA/cm2. For different concentrations of iron salts, alloys (crystallite size, 16-19 nm) with iron content between 0 and 71 mol% conld be obtained. 

Soft magnetic materials are characterized by high permeabiUty and low coercivity. There are sis principal groups of commercially important soft magnetic materials iron and low carbon steels, iron—siUcon alloys, iron—aluminum and iron—aluminum—silicon alloys, nickel—iron alloys, iron-cobalt alloys, and ferrites. In addition, iron-boron-based amorphous soft magnetic alloys are commercially available. Some have properties similar to the best grades of the permalloys whereas others exhibit core losses substantially below those of the oriented siUcon steels. Table 1 summarizes the properties of some of these materials. 

Another area with a large research activity is also related to computer technology. It is electrodeposition of magnetic alloys for thin-film recording heads and magnetic storage media. Here new magnetic materials are needed that have properties superior to those of electrodeposited NiEe (Permalloy). These activities are reviewed by Andricacos and Romankiw (25) and Romankiw (32). 

Magnetically soft Fe-Ni alloys can have their properties altered by heat treatment. The compound NisFe undergoes an order-disorder transformation at about 500°C. Since the susceptibility of the ordered phase is only about half that of the disordered phase, a higher susceptibility is realized when the alloy is quenched from 600°C, a process that retains the high-temperature, disordered structure. Heat treatment of Fe-Ni alloys in a magnetic field further enhances their magnetic characteristics (see Figure 6.61), and the square hysteresis loop of 65 Permalloy so processed is desirable in many applications. A related alloy called Supermalloy (see Table 6.19) can have an initial susceptibility of approximately one million. 

Following a concise review of direct access storage devices, a treatise on the properties and electrochemistry of magnetically soft materials is provided by P. C. An-dricacos and L. T. Romankiw. The chapter is focused on the fundamentals of the magnetics and electrochemistry of Permalloy, a material which has similar importance in magnetic storage as has silicon in semiconductor devices. 

Though NigjjFe , permalloy has superior properties for magnetic recording head core, the film has low resistivity (20 pOcm). Therefore, some researchers have reported permalloys with high resistivity, such as Moco-deposition permalloys [51], Reports also indicate that an increase in the resistivity can be achieved by codeposition with metalloid-forming elements, such as sulfur, carbon, or phosphorus [52, 53], The inclusion of impurities is said to result in an increase in resistivity. Ni jFejj permalloy had been widely used for write head core because the film has high B value (14-16 kG). Ni Fe permalloy co-deposited Mo or Cr is also reportedly in use [54]. 

With regard to magnetic domains, other studies have been devoted to the dynamic properties. Cuomo et al. (1974) showed that bubbles can reach a mobility and velocity higher than 1000 cm/s. Miyama et al. (1978, 1980) studied the effects of applied driving fields, of the temperature and of a permalloy film coating. They noticed a wall velocity as high as 15 000 cm/s for samples with high He- Their sputtered films had an orthorhombic anisotropy. They found a non-... 

---