The switching dynamics in a thin-film head for both the writing and reading modes are studied To minimize magnetostatic energy, the film head is split up into multidomains subsequent to saturation writing in the hard (or track) direction The domain structure is composed of elongated domains in the easy direction and closure domains at the edges The results of our calculation show that domain wall motion contributes increasingly to the effective head permeability as the track width is decreased In the readback process, it was found that the switching time for wall motion τ w (∼170 ns) in the edge domains is some two orders of magnitude larger that τ r for rotation (∼1 ns) in the main domains Since these motions are coupled due to the requirement of continuity of the perpendicular component of \overrightarrow{M_{s}} at a 90° wall, the switching dynamics is dominated by wall motion A finite distribution of wall motion threshold field H o can give rise to different time delays in the head response, leading to distortions in the readback signal, including the presence of wiggles at the trailing edge

Switching dynamics in a thin film recording head

Vector-type magnetic-field sensors suitable for use in a heavy industrial environment and for field measurements include Hall sensors, magnetoresistive sensors and fluxgates. The basic properties of these sensors are discussed. Hysteresis and offset of the permalloy anisotropic magnetoresistance sensors can be lowered by periodically flipping the sensor characteristics. While low-noise fluxgate sensors may work in the sub-nanotesla range and miniature fluxgates may still have nanotesta (nT) resolution, the typical measuring range of permalloy anisotropic magnetoresistors starts at tens of nT and the resolution of ordinary Hall sensors is of the order of 10 μT.

Magnetic sensors for industrial and field applications

A method is described for direct measurement of the magnetic microfield from a recording head. The method employs a thin film ‘‘microloop’’ as a transducer which by induction senses the recording head field. Measurements are presented on both a thin film and a ferrite head. Fits to the data allow the absolute efficiency to be determined. Data on the frequency dependence of head efficiency are also presented.

Direct measurement of recording head fields using a high‐resolution inductive loop (invited)

The interaction between the rotational motion of magnetization and wall movement are investigated for an infinite strip of magnetic film with closure domains. When an external field is applied, the direction of magnetization is assumed to curl parabollicaly near the 90° walls. The 90° wall will move to decrease the energy associated with this curling. This movement can be described by the equation of rotational motion for the wall. The switching time relating to a 90° wall is fairly short (6 - 18 nsec) calculated by solving the equation of motion. It is due to the acceleration of the wall movement by the magnetization rotation.

Mechanism of 90&#176; wall motion in thin film heads

The diameters of the solder joints in the array-array packages can range from 760 /spl mu/m (BGA joints) to 75 /spl mu/am (flip-chip joints). This variation in diameter in fact translates into a 1,000 times difference in volume. Such a large difference in volume produces a pronounced solder volume effect. In this study, the volume effect on the liquid-solid reactions between the Sn3AgxCu (x = 0.4, 0.5, or 0.6 wt.%) solders and Ni was investigated. Three different sizes of solder spheres (760 /spl mu/m, 500 /spl mu/m, and 300 /spl mu/m) were soldered on 400 /spl mu/m diameter electrolytic Ni soldering pads for 90 sec-20 min at a peak reflow temperature of 235/spl deg/C. Two reaction products (Cu,Ni)/sub 6/Sn/sub 5/ and (Ni,Cu)/sub 3/Sn/sub 4/ were present at the interface in all the samples. Interestingly, a massive spalling of (Cu,Ni)/sub 6/Sn/sub 5/ from the interface occurred, especially in samples with smaller solder balls and lower Cu concentration. We attributed the massive spalling of (Cu,Ni)/sub 6/Sn/sub 5/ to the decrease in the amount of available Cu in the solders as the amount of solder as well as the Cu concentration decreased. The results of this study suggested that a high Cu-content SnAgCu solder should be used to prevent this massive spalling.

Volume effect on the soldering reaction between SnAgCu solders and Ni

An introduction to the theory of the anisotropic magnetoresistance effect in ferromagnetic thin films is given, ending in a treatment of the minimalization of the free energy which is the result of the intrinsic and extrinsic anisotropies of the thin-film structure. The anisotropic magnetoresistance effect in long strips is reviewed. Attention is given to problems like the formation of domains and measures like biasing and linearization. The paper concludes with a description of some applications which are being developed by the authors: (1) an analyser for the stray field of recording heads; (2) a sensitive magnetometer; (3) an accurate absolute angle detector; and (4) an absolute (linear) position detector.

/pdf/permalloy-thin-film-magnetic-sensors-2vxc5y8onk.pdf

Permalloy thin-film magnetic sensors

The influence of the trackwidth on the performance of thin film heads has been tested. Results of experiments on the wafer have indicated an increase in the head efficiency with decreasing trackwidth. This was underlined by measurements of the head fringe field and tape recording experiments. A model which takes the domain structure into account has been developed to interpret this behaviour.

/pdf/magnetic-behaviour-of-narrow-track-thin-film-heads-iu46auz2gi.pdf

Magnetic behaviour of narrow track thin-film heads

Materials Science and Engineering - EL

The system described is built around a very accurate positioner into which a sensitive transducer and the object of analysis is mounted. The properties of the applied magnetoresistive transducer are described. This transducer, a very narrow permalloy strip placed at the edge of a glass substratum, can be used to measure both components of the field distribution. The analysis of the measured results can be accomplished with the help of a computer simulation of the transducer response curves. The performance of the system is demonstrated by measurements on a number of ferrite heads and conclusions about the so called 'dead layer'-structures on these heads are given.

/pdf/measurement-system-for-two-dimensional-magnetic-field-t4bbwlshqd.pdf

Measurement system for two-dimensional magnetic field distributions, applied to the investigation of recording head fields

The resistance anisotropy in ferromagnetic conductors gives rise to the related planar magneto-resistive and Hall-effects. The magneto-resistive effect is exploited in several field sensing transducers, while the planar Hall-effect is not. In this paper the output of direct sensing Hall-heads is compared with magneto-resistive heads for a number of situations typical for magnetic recording. The comparison is based on a computational procedure which can be executed with the help of a simple calculator. The procedure and the results are presented in such a way that known results for magneto-resistive transducers can immediately be translated into results for Hall-transducers.

https://ris.utwente.nl/ws/files/6527424/01061672.pdf

J.P.J. Groenland

Papers

Permalloy thin-film magnetic sensors

Magnetic behaviour of narrow track thin-film heads

Materials Science and Engineering - EL

Measurement system for two-dimensional magnetic field distributions, applied to the investigation of recording head fields

Comparison of a shielded "One-sided" planar hall-transducer with an MR-head