Structural and Magnetic Characterization of Electrodeposited, High Moment FeCoNi Films

Abstract

We investigated the electrochemical deposition process of Fe-Co-Ni alloys from sulfate electrolytes containing no organic additives and the structural, magnetic, and electrical properties of the resulting films. The effect of pH and Co and Fe concentrations in the electrolyte on alloy composition is examined. The pH of the solutions is kept at 2.8 to minimize the incorporation of nonmagnetic matter. With increasing Ni content, a transition of the film structure from body-centered cubic ͑bcc͒ to face-centered cubic ͑fcc͒ is observed. X-ray diffraction and transmission electron microscopy results show that the smallest grain size of about 10 nm is obtained when the bcc and fcc phases coexist. Films with biphasic structure exhibit soft magnetic properties ͑coercivity about 1 Oe͒, high magnetic moment ͑about 2.1 T͒, narrow dispersion of the easy axis ͑less than 3°͒, and good high frequency response, with a resonance frequency above 1.8 GHz. Stress anisotropy has an important role in determining soft magnetic properties.Soft magnetic films with high saturation induction B s , low coercivity H c , and high permeability are essential components of write heads in high density recording systems, as well as in integrated thin film inductors and transformers. In particular, Fe 20 Ni 80 ͑Permalloy͒ and later Fe 55 Ni 45 alloys have been almost exclusively used as pole materials for thin film heads. 1 Currently, however, the B s of these materials, 1 and 1.6 T ͑10 and 16 kG͒, respectively, is insufficient to provide the writing field to saturate the magnetic media with high coercivity ͓H c Ͼ 320 kA/m ͑ϳ4000 Oe͔͒ required to store information at the bit density of 100 Gb/in. 2 recording and higher. 2,3 Fe-Co alloys on the other hand are ideal candidates for these applications, as in the bulk they exhibit B s values up to 24 kG, 2.4 times the value of Permalloy. In addition, these materials potentially provide higher roll-off frequencies of the permeability, 4 necessary to enable device operation in the gigahertz range.Electrodeposition offers several advantages in the fabrication of poles for write heads or magnetic components in integrated devices or microsystems. For example, soft magnetic properties ͑usually better than the corresponding alloys made by sputtering or evaporation͒ and low internal stress can be obtained at high rates of deposition. 1 More importantly, the purely additive process of plating through a patterned mask allows easier and better definition and control of small features. Subtractive processes on the contrary must follow blanket deposition by gas-phase methods, and these are usually difficult to implement due to the lack of practical methods for selective etching. 5 Most recently, focused ion beam etching ͑FIBE͒ has shown improvements in this respect, allowing the reliable definition of poles with submicrometer width, at the expense, however, of using a complicated and expensive instrument.High moment Fe-Co bulk alloys exhibit a high magnetostriction, up to about 10 Ϫ4 . 6 To avoid stress-induced degr...

In-depth component distribution in electrodeposited alloys and multilayers

“…It is to be noted that the pH also differs for the two baths used in the above comparison. It is also known [41][42][43] that the mole fraction of Fe and Co in Ni-Co-Fe deposits decrases with the increase in pH if pH >2.8. However, we can exclude that the effect of the pH is dominant in the composition change observed since the initial Fe mole fraction is nearly the same.…”

“…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.…”

Influence of Additive Adsorption on Properties of Pulse Deposited CoFeNi Alloys

“…The crystal structure changing from FCC to FCC+BCC does not seem to induce any measurable change in the magnetic moment of the CoFeNi films (~1.8 T, Figure 7). Previously reported results for CoFeNi films deposited with the direct current (DC) method indicate that desirable region for soft CoFeNi films is the one where either both crystal phases coexist or the alloy composition is on the boundary of the two-phase region 2,3,7,9,33 . Similarly, our data indicate that in the case of the pulse deposited CoFeNi films, the magnetic softness is promoted with the appearance of BCC phase ( Figure 6 -Figure 8).…”

“…Besides a commonly seen action of leveling and brightening of the deposit, the benefit of additives in plating bath was usually attributed to improvement in the grain size and the crystal structure of the deposit 2,3 , stress reduction 4 , suppression of hydrogen evolution 4 , and improved corrosion resistance of the deposit 5 . Recently, it was demonstrated that the appropriate choice of the additives and bath chemistry could substantially improve the magnetic properties of the CoFeNi films 2,6,7,8,9 . Magnetically very soft CoFeNi alloys with coercivity less than 2 Oe and high magnetic moment (>1.8T) were produced leading to substantial breakthrough in electrodeposited magnetic head core materials used for high density magnetic recording 2,7,9 .…”

“…Recently, it was demonstrated that the appropriate choice of the additives and bath chemistry could substantially improve the magnetic properties of the CoFeNi films 2,6,7,8,9 . Magnetically very soft CoFeNi alloys with coercivity less than 2 Oe and high magnetic moment (>1.8T) were produced leading to substantial breakthrough in electrodeposited magnetic head core materials used for high density magnetic recording 2,7,9 .…”