Single-pole writers and TMR readers for 100 Gb/in2 perpendicular recording were fabricated and their recording performance was tested. Data erasure due to remanence magnetization of the main pole in the single-pole writer occurs when the pole width is 200 nm or less. The erasure can be suppressed by reducing the throat height of the main pole. Narrow-track writers with a pole width of 150 nm show good write ability for a medium with high coercivity of 6.5 kOe. The TMR reader shows high sensitivity of 40 mV/μm at a magnetic track width of 124 nm. The half width of the microtrack profile with a perpendicular medium is narrower than that with a longitudinal medium. This is due to a larger spacing loss for low-linear-density data in perpendicular recording. The noise in TMR heads is dominated by the shot noise.
We developed a magnetooptical probe system for measurement of high-frequency current in magnetic heads. The key technique of the system is magnetooptical probing using a Bi-YIG field sensor. This technique enables nondestructive and noninvasive measurement of the device under test. The system bandwidth is more than 6 GHz. The insertion impedance is negligibly small for magnetic heads. The minimum detectable current is less than 0.3 mA peak-to-peak. Therefore we can perform precise measurements of current waveforms which correspond to real currents in hard disk drives.
We theoretically study quantum oscillation of tunnel magnetoresistance recently observed in junctions with a nonmagnetic spacer inserted at the interface. It is shown that momentum selection due to the insulating barrier and new conduction channels via quantum well states due to the disorder are crucial to explain the observed period of the oscillation in the TMR ratio and its asymptotic behavior.
A magnetic actuator for colonoscope navigation was fabricated. We then examined a motion test using the intestine of a pig. The actuator was composed of a tubular permanent magnet and a spiral structure made of rubber. The magnet was magnetized in the direction of its diameter. The actuator was attached to the end of a simulated endoscope. When a rotational magnetic field is applied, the actuator rotates and moves in the intestine tube. The magnetic actuator can trail two flexible silicone tubes in the small and large intestines of a pig without changing the shape of the intestines. This result suggests that the actuator has great potential for colonoscope navigation.
The basic equations of incompressible viscous fluid flow were integrated using the three-dimensional finite volume method. We calculated the flow field around the micro-machine was to estimate the swimming velocity, thrust, drag, and load torque of a spiral-type magnetic micro-machine. The swimming properties of the micro-machine were analyzed theoretically. We obtained good agreement was between the experimental and theoretical results, on which basis we judged a technique for three-dimensional analysis to be established.
It is reported that magnetic stimulation is efficacious in treating urinary incontinence. Magnetic stimulation has two main advantages over electrical stimulation: it can be applied without removal of clothes, and it involves little pain. However, the distribution of current in the living body is not clearly known. We therefore attempted to create a computer simulation model of the female abdomen and to simulate the distribution of induced current on the basis of tissue conductivity. This report compares electrical with magnetic stimulation.
We measured magnetic alpha waves using a 195-channel, whole-head vector magnetoencephalogram (MEG) system for detecting three magnetic field components (Br, Bθ, Bφ). The reference signal of the Br component was determined by power spectrum density of each hemisphere, and coherence analysis of Bθ and Bφ components was performed using the reference signal. The results of coherence analysis with Bθ and Bφ components showed high coherence values for each hemisphere. We found that two different sources existed for the magnetic alpha wave. It was confirmed that coherence analysis using Bθ and Bφ components was useful to separate multiple sources of magnetic alpha waves.