Peter Vandersalm Koeppe

Kerr effect imaging of dynamic processes in magnetic recording heads

Techniques for imaging microscopic dynamic magnetic phenomena in magnetic recording heads are reviewed. Two experimental apparatus which utilize the Kerr magnetooptic effect are described. A scanning magnetooptic photometer uses the principles of confocal optical microscopy in which a focused laser spot serves as a high-resolution ( approximately 0.3 mu m) probe of magnetic activity to very high frequencies (250 MHz). Magnetooptic flash photography uses the technique of stroboscopic imaging with digital image processing to provide instantaneous (10 ns exposure time) images of magnetic phenomena on a microscopic scale by utilizing a pulse laser for illumination. Results from various studies of ferrite, metal-in-gap, and thin-film magnetic recording heads using these apparatus are reviewed along with their methods. >

Exchange coupled NiFe-TbCo thin films for use in self-biased magnetoresistive heads

It is found that the exchange field produced at the NiFe-TbCo interface has a maximum value at a TbCo layer composition of 27.5%. When proper sputtering conditions are used, this deposited composition produces an exchange field as large as 500 Oe when the layer is coupled to a 370-AA Permalloy layer. Torque and VSM data indicate that the TbCo layers have both in-plane and perpendicular anisotropy components and that the in-plane M-H loops of films that produce the maximum exchange field are square. A linear decrease in exchange field is observed as the NiFe layer thickness increases. The exchange field is independent of the TbCo layer thickness in the range of 1000-4000 AA. Films with a 500-AA layer of TbCo exhibited a greatly reduced exchange effect. A preliminary 500-AA-thick 128- mu m*20- mu m permalloy head biased with 2000 AA of TbCo exhibited at Delta R/R of 1.45%. The hard-axis coercivity is negligibly small ( 1 MHz. >

Very high sensitivity GMR spin-valve magnetometer

A NiFe/Co/Cu GMR spin-valve magnetometer is designed, built, and tested. Thin-film flux-concentrators provide 50/spl times/ gain, yielding hysteresis-free sensitivity 1/R dR/dH=11%/0e in a 1 mm/sup 2/, internally temperature compensated device. Detection levels of 2 /spl mu/Oe/(Hz)/sup 1/2/ (at 1 Hz) are limited by 1/f resistance noise in the GMR films, which is examined in detail. Improvement by 10/spl times/ is possible via increased device size, as well as lower noise MR films.

Direct observation of the dynamic magnetic action in metal-in-gap recording heads

The behavior of the dynamic magnetic switching of metal-in-gap recording heads, observed directly through the use of the magnetooptic Kerr effect, shows significant magnetic action in the vicinity of poorly formed interfaces between Sendust and ferrite. A series of MnZn ferrite heads with increasingly better interfaces between the ferrite and Sendust is examined, and results from magnetooptic measurements are correlated with recording characteristics on media with coercivities of 900 Oe. No magnetic discontinuity at the interface of the best head is detectable by either technique, demonstrating that careful control of the interface can enhance the magnetic coupling between Sendust and ferrite to an acceptable level for suitable recording characteristics on such media. >

Effect of pole tip alignment on magnetic fringing fields from recording heads

The effect of using pole tips of equal width in thin‐film recording heads has been studied by examining a head having the track edges of its leading and trailing pole tips virtually aligned on one side and misaligned by 1.5 μm on the other. Magnetic fields produced by this head, as well as by a head whose edges were aligned by ion milling, have been measured. Using a magneto‐optic photometer system with spatial resolution of less than 0.5 μm, the response of a thin‐film medium spaced 0.25 μm from each head was dynamically monitored at a frequency of 1 MHz as the head was scanned beneath it. Results demonstrate that fringing fields emanate to a larger spatial extent in both dimensions from misaligned edges. These results are correlated with magneto‐optic measurements of the dynamic response of the magnetization made directly at the pole tips of the two recording heads. Both a wider written track and broader transitions of magnetization are to be expected in a magnetic storage medium subjected to the fields...

Thin-film head domain structures versus Permalloy composition: strain determination and frequency response

The influence of the composition of plated Permalloy on the resulting magnetic domain structure in the upper yoke of inductive thin-film magnetic recording heads has been investigated. The response of the magnetization from four otherwise similar thin-film heads, ranging in iron content from 18 to 21% by weight, has been imaged by means of a scanning magnetooptic photometer. Radially compressive (and/or circumferentially tensile) strain is shown to exist in each of these heads about the rear magnetic closure, yielding a transition from radial to circumferential domain structures across the range of compositions. Mechanisms for the conduction of magnetic flux in each of these structures are demonstrated at 1 and 20 MHz. >

Response of magnetization to high frequency excitation in inductive thin-film recording heads

A scanning magnetooptic photometer system was used to study the high-frequency response of magnetization in inductive thin-film recording heads. Measurements at 40 MHz show that most domain walls cease to move at this frequency. At the surface of these motionless walls, the magnetization does not respond to the applied field, forming a dead surface layer. On the two sides of these motionless domain walls, magnetic flux conduction is by nonuniform rotation in the sense that both the rotation angle and the phase are different at different places, forming magnetic flux ripples. Locked ripple was previously shown to significantly slow magnetization reversal in thin Permalloy films, and these measurement results indicate it will likely limit high-frequency performance of thin-film heads as well. >

Magnetic properties of sputtered bilayer and laminated CoZrRe/SiO/sub 2/ thin films

Multilayered CoZrRe/SiO/sub 2/ films have been investigated in an effort to increase permeability of soft amorphous CoZrRe films at high frequencies. The effects of SiO/sub 2/ layering on coercivity, anisotropy and permeability are presented. The magnetic characteristics are dependent on the deposition parameters and thickness of both the CoZrRe and the SiO/sub 2/ layers. CoZrRe films with SiO/sub 2/ overlayers exhibit greater resistance to annealing with increasing SiO/sub 2/ input power. This is attributed to substrate heating with increasing input power that anneals the CoZrRe film during deposition. The coercivity of the multilayered films is less than that of a single CoZrRe layer. As the SiO/sub 2/ thickness increases, the coercivity of the multilayer film increases. These results are explained in terms of magnetostatic coupling between CoZrRe layers. Magnetooptic permeability measurements indicate good response at frequencies above 10 MHz for laminated films. >

Future Recording Enhancements For Increased Data Storage In The Advanced Photo system

Although the entire width of Advance Photo System film is coated with magnetic particles, only the edges are currently used for recording digital data. In developing increased data storage capacity using the image area of the film, new ways of modulation encoding the data, read heads with increased sensitivity, and novel ways of achieving good head-to-media compliance are required to meet the challenges of large media speed variations, low magnetic particle loading, and complying to stiff media.

High-resolution magnetooptic imaging of the high-frequency magnetic behavior of ferrite recording heads

The magnetic response in the vicinity of the gap of a ferrite recording head has been imaged magnetooptically at frequencies of up to 50 MHz with a spatial resolution of under 0.5 mu m. The measurements show that different grains in the ferrite provide different amplitude and phase of response, presumably as a result of their different crystalline orientations. Magnetic activity across grain boundaries is evident, indicating small magnetic discontinuities between grains. The results graphically demonstrate the potential for magnetic nonuniformities in polycrystalline ferrites, and they show that heads using such ferrites may exhibit less than desirable behavior for track widths nearly as narrow as the grains. >