James L. Su

Track edge phenomena in thin film longitudinal media

Isolated transitions recorded with a thin-film inductive head on thin-film isotropic media and read with a magnetoresistive sensor can exhibit waveform distortions characterized by a shift of the base line between readback pulses. The amount of the base-line shift (BLS) increases with increasing write current, decreasing trackwidth, and decreasing medium coercivity. The source of the BLS is shown experimentally to be localized at track edges. A model based on the creation of magnetic dipoles along each edge of the data track is proposed to explain the observed waveform deformation. The width of the dipole distribution is estimated by deconvolving a measured BLS track profile with a measured readback-sensitivity track profile. Calculated BLS profiles based on this dipole model agree well with the experimental observation. >

Laminated CoZr amorphous thin‐film recording heads

Recording heads with four‐layer laminated CoZr/Ta films as pole pieces have been fabricated using rf sputter deposition and ion milling techniques. Typical 4πMs of 14 000 G were obtained for CoZr amorphous films compared with 10 000 G for Permalloy films. Recording tests performed with this laminated CoZr/Ta film head indicate 8–12 dB better overwrite than with plated Permalloy film heads having an identical structure. However, the former exhibits a 10%–25% lower amplitude than the latter. This may be attributed to the thermal degradation of the initial permeability μi of the CoZr film during head‐fabrication processes. This CoZr/Ta head also shows poorer amplitude stability than the plated Permalloy head.

Side fringing of thin film heads with pole trimming

A technique for measuring write and erase widths using a narrow-track MR (magnetoresistive) probe to acquire the dual-track profiles of write/overwrite tracks has been developed. This technique was used to reveal the distinct features of shoulder effects on the side-writing and side-erasing behavior of pole-tip trimmed heads. Another technique, using the microtrack profile, was utilized to demonstrate the impact of the low shoulder on the side reading of trimmed heads. Trimmed heads which have a shoulder within 5 mu m of the air-bearing surface exhibit modified side-fringing characteristics for the heads and disks studied. The trimmed heads with a shoulder height exceeding 6 mu m show substantially smaller erase and read widths, and a weaker dependence of write width on transition density when compared with an untrimmed head having unequal pole widths. >

Noise in disk data-recording media

Measurements were made of recording medium noise in erased disks using an in-contact magnetoresistive element and an inductive head supported on an air bearing slider. Four types of coatings on aluminum disks were examined: thin, transition-metal alloy film, CrO,, FeCo particle, a n d y-Fe,O:,. Results obtained by means of three measurement techniques are in qualitative agreement and indicate that: (1) dc-erased noi\e of alloy film disks is 14 to 20 dB lower than that of particulate disks measured; (2) dc-erased noise of particulate disks measured is 6 to 16 dB above their bulk-erased noise: (3) although dc noise of particulate disks increases with write current, dc noise of alloy film disks is independent of write current: (4) the shapes of the noise spectra are similar in dc-erased particulate y-Fe,O, disks and FeCo particle coated disks: and (5) significant modulation noise is detected on particulate disks but not on alloy film disks. The observed dc-erased noise spectrum is compared with the model for small particle noise and is then used to estimate the size of particle agglomerates or voids. Introduction Several theoretical and experimental investigations of noise in magnetic tape systems have been published [ 1-61, but until recently there was little interest in measuring the corresponding noise in disk surface media because it does not limit performance of present disk data storage systems. Disk noise measurements are of theoretical interest because of the relatively well-known head-medium spacing and the expected absence of noise caused by surface irregularities, tape flutter, and inverse magnetostrictive effects associated with head-tape contact. Although most tape noise studies have emphasized the noise of ac-erased media, the emphasis here is on the dc-erased, or uniformly magnetized, state which resembles the saturated digital state. The dc-erase noise provides information about the homogeneity of the magnetic medium, and its measurement can shed light on the suit-ability of the medium for use at high storage densities. The difference between the observed noise power spectrum and that which would be caused by small particles is interpreted as the noise spectrum of the inhomogenei-ties. Measurements of particulate coatings, both here and in the literature, indicate higher noise levels for dc erase than for ac erase. For comparison, measurements are presented here of a thin transition-metal alloy film medium, for which the reverse is true.

Omega head—an experimental 120‐turn inductive head

Experimental 120‐turn thin‐film inductive heads have been built. The key features of this head are the 6‐μm pitch helical coils and an omega‐shaped, planar yoke structure having dual easy axes. Hardbaked photoresist insulator layers are used to encapsulate the yoke and to smooth out the wafer surface topography. Micro‐Kerr studies show that the easy axis remains in the transverse direction in the yokes after multiple anneals. The P1/G/P2 is 3.8/0.3/3.8 μm, and the yoke length is close to 1 mm. The helical coils were built with a novel process that combines yoke/stud coplating and a photoresist planarization process. The coil resistance is 68Ω and the inductance is 5.5 μH. The yoke saturates at 5 mA. The heads were tested over disks having Mrt of 2.5 memu/cm2 and Hc of 1500 Oe. The write threshold current is 5.3 mA (peak‐to‐peak) and the overwrite is 30 dB. The isolated pulse amplitude Vpp is 10.3 μV/(TwV), where track width Tw is in μm and the linear velocity V in m/s.

Thin film head with staggered pole tips

The authors propose a cost-effective approach to reduce write track widths down to the sub-micron range. Thin-film heads with staggered pole tips, such that the track width is defined by the overlap of pole tips, have been fabricated with processes similar to the conventional thin-film head process. Both the transverse and the longitudinal configurations have been examined. Heads of both configurations have worked well, achieving satisfactory overwrite performance and track definition. Narrow track write heads capable of writing transitions as narrow as 0.7 mu m have been demonstrated. such sub-micron write heads hold potential for achieving high track densities in conjunction with magnetoresistive read heads. >

The anisotropy dependence of bubble dynamics in EuGaYIG films

We have studied the dynamic properties of bubbles in a series of oxygen‐annealed EuGaYIG films which have similar magnetic properties except for decreasing uniaxial anisotropy as a function of anneal time. The translational saturation velocity and skew angle of bubbles translated in a pulsed gradient field experiment increase as the anisotropy decreases. These results are in agreement with theoretical predictions of a Ku−1/2 dependence. We also observe that for a given anisotropy and bubble state (S=1), the skew angle decreases as the drive increases, in agreement with theory which predicts that if the velocity is saturated, drive and angle are inversely related.

Side-writing phenomena in isotropic film media

The isolated readback pulses of magnetoresistive (MR) heads on isotropic film media have been reported to exhibit base‐line shifts. We have further observed that for piggyback MR (PMR) heads with thick pole‐tip write elements operating at high write currents, an additional base‐line shift occurs, thereby producing dual‐base‐line shifts. This second base‐line shift results in anomalous signal‐amplitude variations as the transition density increases. Moreover, the onset of the second base‐line shift occurs ahead of the readback pulses at a distance equal to the trailing‐pole thickness. We attribute the second base‐line shift to the trailing‐pole side writing, which modifies the magnetic dipole distribution along the track edges prior to the transitions at a distance equal to the trailing‐pole thickness.

Rapid and nondestructive measurement of the anisotropy field in bubble garnet films

A microwave resonant cavity has been developed for nondestructive ferromagnetic resonance (FMR) measurements of bubble garnet films. The cavity allows the examination of intact wafers up to 3 inches in diameter. The cavity design and the results of FMR studies using this cavity are reported. The typical measurement time of the effective anisotropy field H k - 4πM s in bubble films with the precision of ±1% is less than 30 s. The results are compared with an improved magneto-optic method which requires the measurement time of 5 min with the precision of ±4%.