Mark T. Kief

Effect of Magnetic Field on Electrode Reactions and Properties of Electrodeposited NiFe Films

Enhancement of current for solutions, containing Ni +2 , Fe +2 , and H + ions, has been observed by linear sweep voltammetry and chronoamperometry when a magnetic field of 0.1 T was applied parallel to the cathode. The current enhancement in a magnetic field was attributed to the convection near the electrode surface induced by the Lorentz force. There is a decrease of the Fe content in NiFe films by approximately 4% obtained with applied magnetic field. It was also demonstrated that the applied magnetic field affects the magnetic properties, crystalline structure and/or texture, stress, and surface roughness of NiFe films.

Mechanism of Saccharin Transformation to Metal Sulfides and Effect of Inclusions on Corrosion Susceptibility of Electroplated CoFe Magnetic Films

The electroplated magnetic alloys 1.0T Ni80Fe20, 1.6T Ni45Fe55, 2.4T Co40Fe60, obtained in the presence of saccharin, and sputtered magnetic alloys of the same composition showed dramatically different corrosion properties at pH 5.9. The higher corrosion susceptibility of electroplated magnetic alloys, known for many years, was generally attributed to sulfur inclusions into the deposit. However, there was no direct evidence of the structure of sulfur-containing molecules included in deposit. We have analyzed electroplated, EP-CoFe, and sputtered, SP-CoFe, magnetic films using electrochemical, secondary ion mass spectroscopy, X-ray photoelectron spectroscopy XPS, and high-pressure liquid chromatography HPLC techniques. The analysis of electroplated CoFe films obtained in the presence of saccharin revealed saccharin, benzamide, o-toluenbenzamide HPLC and metal sulfides XPS in EP-CoFe deposit. The proposed mechanism for saccharin transformation to metal sulfides involves four steps: i a reductive cleavage of C-S bond in saccharin giving rise to benzamido sulfinate, ii a desulfurization step leading to benzamide and sulfur dioxide, iii an electrochemical reduction of sulfur dioxide to hydrogen sulfide, and iv a reaction between H2 Sa nd M +2

Structure, stress, and magnetic properties of high saturation magnetization films of FeCo

Thin (/spl sim/2000 /spl Aring/) films of Fe/sub 60/Co/sub 40/ have been prepared by sputtering on Si/SiO/sub 2/, Si/AlO/sub x/, AlTiC/AlO/sub x/, AlTiC/AlO/sub x//NiFe, and AlTiC/AlO/sub x//NiFeCr substrates using an alloy Fe/sub 60/Co/sub 40/ target. The structure of the films was characterized by means of X-ray diffraction and transmission electron microscopy (TEM). Surface roughness was characterized by atomic force microscopy (AFM). Stress, transport, and magnetic measurements were conducted. We observed correlation in the following pairs of properties: coercivity-stress, grain size-stress, and coercivity-grain size. Although individual films had a stress in the wide range of compressive 2.5/spl times/10/sup 10/ Dyne/cm/sup 2/ to tensile 1.3/spl times/10/sup 10/ Dyne/cm/sup 2/, which depended to some degree on the material of the substrate and underlayer, we found that biaxial stress and coercivity seem to be described by a general trend, with coercivity being as low as 19 Oe at intermediate tensile stress and as high as 225 Oe at high compressive stress. The unstrained lattice parameter and Youngs modulus of the alloy Fe/sub 60/Co/sub 40/ were also determined.

Comparing theoretical demagnetizing factors with the observed saturation process in rectangular shields

An analytic expression is given for the ballisticdemagnetizing factors, D ′ , of the general rectangular prism, in which the field is averaged over the middle cross section of the prism, and for the “side” demagnetizing factor, D ″ , in which the averaging is over the edges of the prism. The demagnetizing fields are compared with the applied field values when a 250×95×2.35 μ m magnetic shield transfers into the saturated state. This shield was made of a Ni 80 Fe 20 film, with a small uniaxial magnetic anisotropy induced during the electroplating process. Domain structure and the process of magnetic saturation were imaged using wide-field Kerr microscopy in fields up to 400 Oe, both along the easy and the hard axes. The ballisticdemagnetizing field is found to be close to the external field necessary to align magnetically the central part of the shield, while the full shield saturation takes place at a field above the recently published magnetometric demagnetizing field. Saturation fields along the hard uniaxial anisotropy axis are larger, due to effective anisotropy fields.

High saturation magnetization films of FeCoCr

Thin (∼1000 A) films of (Fe54Co46)1−xCrx have been prepared by magnetron sputtering on Si/SiO2 substrates. The films were shown to be body-centered-cubic and (110) textured. It was found that the Fe54Co46 films possess a saturation magnetization of 24.5 kG at room temperature. Doping the Fe54Co46 films with Cr in the range of 0–13 at. % increased corrosion resistance, electrical resistivity, and reduced the saturation magnetization as a function of the amount of added Cr. The coercivity of both doped and undoped as-deposited films (80–120 Oe) decreased substantially after a 220 °C magnetic anneal. Electrochemical corrosion testing was done in two chloride salt solutions. Potentiodynamic scans performed on films in a 0.47 M chloride bath solution at pH=2.9 showed a substantial increase in corrosion resistance of the films between 6.6 and 8.2 a/o Cr. Similar scans performed in a 0.01 M chloride solution at pH=5.8 showed good corrosion resistance for all the films.

Effect of Magnetic Field on NiCu Electrodeposition from Citrate Plating Solution and Characterization of Deposit

The effect of an external in-plane magnetic field (B = 0.1 T) on the electrodeposition of NiCu films from a citrate bath solution was studied. The application of the magnetic field showed the following effects: (i) an increase of limiting current for Cu 2 + reduction, (ii) an increase of plating rate of NiCu by ∼17%, (iii) an increase of Cu content in NiCu deposit of 4.9%, (iv) a decrease of tensile stress on NiCu films, (v) a strong influence on the texture, and (vi) a strong influence on surface morphology resulting in three-dimensional (3D) growth without applied magnetic field and 2D growth with applied magnetic field.

Interface coupling and magnetic properties of exchange-coupled Ni81Fe19/Ir22Mn78 bilayers

Hysteresis loop measurements using magnetooptic Kerr effect magnetometry in the low frequency region and magnetization dynamics measurements using high frequency permeametry are carried out to study the exchange anisotropy in Ni81Fe19/Ir22Mn78 bilayers. These two measurement techniques provide different exchange anisotropies for bilayers with thin Ir22Mn78 films. The observations can be understood by assuming that the AF grains break into domains due to the interface random field. By analysing the results from these two techniques, the interface coupling strength and the magnetic properties of the bilayers can be quantitatively determined.

High Magnetic Saturation Poles for Advanced Perpendicular Writers

Advanced perpendicular writers continue to demand maximum write fields, fast rise times at ever vanishing head-media spacing and strict reliability standards. This means that the asymptotic progression to a 2.4 T pole with nearly ideal magnetic response continues. At the same time we must control critical pole dimensions, fabricate at a reasonable cost while protecting against corrosion and erasure risks. We will review progress made to meet this challenge in a discussion of high moment materials utilizing electroplating and sputter deposition for single layer films and laminates. Concerns for corrosion will be assessed and minimized by controls on key contaminants. Micromagnetic modeling will be used to study the phenomenology and expected performance impacts of these various materials and structures. Results will be used to provide a better insight into the potential materials/design tradeoffs that must be made. In conclusion, performance and reliability will be assessed through electrical testing.

Magnetic anisotropy of (110) Fe∕Co superlattices

Magnetic anisotropy field of (110) Fe∕Co superlattices was found to be as high as 1T, with an in-plane easy axis. First principles calculations within the local spin density approximation show good agreement with the measurement. Lowering the symmetry by creating artificial superlattice structures leads to a significant increase in magnetic anisotropy energy as compared with any allotropic form of the elemental components and cubic FeCo. Large anisotropy is attributed to the cubic symmetry breaking due to the multilayer artificial atomic arrangement. Dependence of the anisotropy field on the superlattice period is supported by Monte Carlo film growth modeling.

Kerr effect observations of magnetization reversal process in antiferromagnetically pinned permalloy thin films

In this article, the magnetization reversal process for antiferromagnetic (AFM) materials (NiO, FeMn, and NiMn) coupled to NiFe permalloy thin films have been investigated. The nature of the effect of exchange coupling on the reversal of the AFM-pinned permalloy was observed using the magneto-optic Kerr effect. These studies indicated that the reversal process appears as widespread nucleation of 1–10 μm sized reversal domains over the entire area of the film with subsequent domain expansion and coalescence. Interpretation of the magnetization reversal process requires an understanding of the exchange coupling mechanism. It is believed that the magnetization reversal process observed here is dominated by a nucleation-rotation mechanism in which the interfacial spin system is highly uniform. The exact nature of the spin reversal nucleation process is not fully understood but appears to arise from weak localized pinning states.