The giant magnetoresistive (GMR) recording head is extremely sensitive to external magnetic field. Since it is anano-scale electronic device, various unpredictableeffects, i.e., electrostatic discharge (ESD) and parametric effects, exhibit. It has been found that a d. c. voltage of an order of about 1 V across the head is harmful. In this report, the effect of magnetic field radiated by an electromagnetic interference, EMI, phenomena in aspin-stand recording head tester is studied. It is seen fromresults that the field strength produced by a reverse biasheadset is about twice higher than that by a forward biasheadset. This is possibly due to the remanence in magneticelements or even in the headset itself. It is also found froman estimated calculation that EMI may induce the voltagedrop across GMR head as highly as about 35 m V which ispossibly strong enough to interfere the head performance.

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We investigated both the read/write performance for sub-micron bits and the possibility of recording servo-patterns of over 300 Gbits/in2 by using patterned master contact duplication, which is expected to resolve the problems of conventional servo-track writing. The experimental value of the spacing loss factors forsub-micron bits resulting from the duplication was around 20 dB, which was lower than that for reportedcon ventional magnetic head recording. The reason for thelow value is that the duplication suffers less from recording demagnetization because a static recording method is used and the S* value of the slave is high. A reading experiment involving duplication using a master disk with a track width of 190 nm and a bit length of 123nm yielded a signal-to-noise ratio of 17.9 dB, which was a little larger than that of magnetic head recording. The simulation of a magnetic field to duplicate a high-density servo-pattern indicated that the magnetic field was large enough to record servo-patterns of as much as 370 Gbits/in2. These studies demonstrated the potential of this method for high-density servo-pattern recording.

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Ga ion irradiation was used to modify the microstructures and magnetic properties of Co/Pd multilayers and also to fabricate patterned media. A decrease in the diffraction peak at low-angle XRD showed that the regular interface between Co and Pd layers was blurred by ion irradiation. The effective perpendicular magnetic anisotropy energy, K_eff, decreased from 1.7×10⁶erg/cm³ for as-grown film to 0.4 ×10⁶ erg/cm³ for irradiated film at 2×10¹⁵ ions/cm². The easy axis of magnetization changed from perpendicular to in-plane atthe highest ion dose (5×10¹⁵ ions/cm²). An MFM imageshowed that the domain width gradually decreased with increasing ion dose, which corresponds to a decrease in the perpendicular magnetic anisotropy. Sharp boundaries between perpendicular and in-plane regions are also observed in patterned films, which indicates that localized magnetically patterns can be engineered by Ga ion irradiation.

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We carried out a three-dimensional vector measurement of a somatosensory evoked field (SEF) with an electric stimulus to the right thumb, using three-dimensional second-order gradiometers connected to 39-channel SQUIDs, which can detect magnetic components perpendicular to the scalp (Br) and tangential to the scalp (BΘ, Bφ) simultaneously. A dynamic singular value decomposition method, with a time window and shift time, was applied to spatio-temporal magnetic data. First, averaging of the SEF data with a dynamic SVD was done with each trigger for stimulation. Second, dynamic SVD was applied to SEF data, having two frequencies ranges (1-80 Hz and 15-80 Hz), and with a time window of 10 ms and which was shifted every 1 ms in analysis. Two dominant singular values were obtained for the contralateral magnetic component in 90 to 110ms. Source localization of SI and SII activity with a ECD method showed dominant GOF (goodness of fitness) around 90ms. We concluded that the proposed dynamic SVD method, with a time window and shift time, is useful for reducing noise component in SEF data and discriminating multiple sources overlapping in time.

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