Tadayuki Iwakura

Inductance and Read-Write Characteristics for Thin Film Heads

The inductance and read-write characteristics for thin film heads with various magnetostriction constants were investigated. Heads consisting of a top yoke with positive magnetostriction constants and a bottom yoke with negative constants, exhibited excellent read-write characteristics. Such a result can be explained by an increase in the difference between the inductance at zero bias, and that when the core pieces are magnetized, that is, by the permeability of the core pieces. High permeability was caused by the magnetoelastic effect based on the induced uniaxial stresses in permalloy films. In addition, the overwrite level improved dramatically as certain values of the bias magnetomotive force, determined from the inductance characteristics, increased. It was concluded that the measurement of the inductance characteristics is a very powerful method for evaluating the performance of pole tips and taped regions of thin film heads.

Effect of Side-Fringing Field on Read-Write Characteristics for Thin Film Magnetic Heads

The side-fringing fields of thin film heads were studied using three-dimensional simulations. Playback signals were calculated using the reciprocity principle. The output as a function of linear density was calculated by superpositioning of isolated pulses. The results of three-dimensional calculations of isolated pulses, off-tracking and output as a function of linear density, agreed with measurements. These calculations and measurements indicated that the effect of the side-fringing field appears in the isolated pulses from narrow-track heads. It was found that asymmetry in isolated pulses results from the effect of the side-fringing field. By narrowing the track width, the effect of the side-fringing field is increased. Playback pulses from the outside of the track are broader than those at the track center, and so the resolution of narrow-track heads decreases.

Read-Write Characteristics of an NiFe/CoNiFe Laminated Thin-Film Head

The read-write characteristics of thin-film heads with a NiFe/CoNiFe laminated upper pole were studied. Compared with NiFe heads, NiFe/CoNiFe laminated heads are better able to suppress loss of output and increases in disk noise, and provide better overwrite characteristics. Comparison of experimental and calculated results indicate that pole saturation causes an increase in the transition length, because of the field gradient decrease, which results in an output decrease. The decrease in head efficiency due to the increase in the CoNiFe layer thickness is negligible if the latter is less than 20% of that of the upper pole. NiFe/CoNiFe laminated heads are deemed promising for high linear density recording.