MR Element Research Articles

An Ultra Low-Power MR*1) Sensor for a Smart Water Meter or a Smart Gas Meter

A new ultra low power MR sensor comprising MR elements integrated with Bi-CMOS IC chip, which is optimal for the use in smart water meters and gas meters playing important role in global smart gridization, has been developed. MR elements are configured as a Wheatstone bridge circuit. MR element patterns are placed in the perpendicular configurations as resistive components of the circuit. Those detect the magnetic field applied to X and Y axis respectively, and then outputs either high or low-level electric signal. Optimization of the MR element pattern aspect ratio (ratio of the element length to the element width) and configuration of the two-row parallel MR patterns in a longitudinal direction enable the equivalent current flow in the direction. This provides mutual magnetostatic coupling and cancellation of each demagnetizing field, and led to achieve minimizing the hysteresis of the resistance change rate affected by up and down of the applied magnetic field. Furthermore, this led to the improvement of mutual symmetry for both S to N and N to S direction of the magnetic field. This resulted in enhanced magnetic sensitivity and successfully obtained magnetic sensitivity higher than 0.8kA/m. For the power supply of the MR sensor, external intermittent control was adopted. Furthermore, active (on) time of the MR element was considerably shortened by utilizing the internal circuit of the IC. As a result, the sampling time was shortened to 1μs and the drive current of MR sensor was reduced to 0.3 μA. *1)MR: Magneto-resistance

High Level Oscillations With Narrow Linewidth in Magnetic Nano-Contact Spin Torque Oscillator With Synthetic AF Spin-Valve Structure

We investigated the current induced magnetization dynamics, so called spin torque oscillation, in magnetic nano-contact MR element with a synthetic antiferromagnetic type spin-valve structure under high in-plane applied magnetic field of 0.9-1 kOe. Very high level oscillation of 18 nVHz-1/2 with narrow FWHM of 12 MHz was observed in the condition of negative applied current where electron-spin is injected from free layer to reference one. Applied current dependency on an oscillation frequency is a blueshift with good linearlity, and same dependency on level and FWHM is almost constant in the range of -10 to -14 mA, while applied field dependency on frequency shows redshift with two different slopes, -2.5 MHz/Oe in less than 1 kOe and -8.7 MHz/Oe in more than 1 kOe which field is smaller than the spin-flop field for the synthetic antiferromagnet, besides very clear and reasonable peak and bottom for oscillation level and FWHM are observed, respectively. It is thought that these magnetization dynamics are originated from synthetic antiferromagnet.

有限要素法を用いたフラックスガイド型半導体磁気抵抗素子の解析

We investigate the magnetoresistance of a magnetoresistive element consisting of a nonmagnetic semiconductor, four electrodes, and a metallic shunt, with varying locations of the voltage electrodes. The optimum location of the voltage electrodes is estimated from MR ratios calculated by using the finite element method. The MR ratio of 6.9%, which was obtained at an applied magnetic field of 0.005 T for an MR element with asymmetrical voltage electrodes separated by a distance of 25 nm, is higher than that for the MR element with symmetrical electrodes. In order to improve the MR ratio at a low applied field, a flux-guide-type MR element is proposed in this study. An MR ratio of 124% at an applied field of 0.005 T was obtained for a flux-guide-type element with asymmetrical electrodes.

Magnetic Field Imaging by Scanning Magnetoresistance Microscope with MR Cantilever

We developed a micro-fabricated cantilever with an MR sensor (MR cantilever) for use as a scanning magnetoresistance microscope (SMRM). Using a four-point MR cantilever with good signal-to-noise ratio, we have succeeded in imaging the stray field distribution of a magnetic garnet sample. Since the magnetic spatial resolution of the SMRM depends only on the physical dimensions of the MR element, the 5-μm by 1-μm MR element used in this study provided a submicronmeter spatial resolution in one direction of the SMRM.

Improvement of the MR Cantilever for Scanning Magnetoresistance Microscope

We have developed the micro-fabricated cantilever with an MR sensor (MR cantilever) for scanning magnetoresistance microscope (SMRM). In order to improve the stability of the MR signal acquisition and the reproducibility of the system, we have proposed a new fabrication procedure for the SMRM cantilever. The MR cantilever with a high field sensitivity is realized and allows us to measure magnetic field quantitatively only for the relatively large external field. However, for the small field detection, superposition of topographic signals on the magnetic signals is not negligible. To avoid this problem, four-terminal SMRM cantilevers were fabricated. In addition, we accomplish to make the cantilever with a high spatial resolution by miniaturizing the MR element.

Non-destructive defect detection scheme using Kerr-channel optical surface analyzer

Magnetic defects on the surface of magnetic disks, unlike normal topological defects, are difficult to detect because they are solely due to magnetic signal loss as seen by the MR element and often do not have any obvious topological features. Defects without any topological features usually render conventional defect finding techniques such as visual inspection, optical microscopy, and SEM useless. In the past, the painstaking way of locating the defect was to index the drive with a strobe light and followed with ferrofluid decoration of the surface to determine the location of the defect. The disadvantage is that the magnetic particles in the decoration technique can often confound the origin of the defect. Furthermore, the old technique does not have high enough resolution to locate defect with a size on the order of a micrometer. In this work, we describe how a magnetic marking technique (MMT) is utilized to circumscribe the magnetic defects. The markers are written in such a way that both the defect and the magnetic markers are easily detected using a Kerr-channel optical surface analyzer and magnetic force microscope. Typically, the accuracy of locating the defect using the MMT is within a track-pitch radially and within one data sector circumferentially. The new scheme provides at least one order of magnitude improvement in detection resolution over the old technique.

A closed-form MR tape head PES model

A closed-form phenomenological expression for the convolution of a MR head microtrack profile with a written track profile is derived. Trapezoid shapes with unequal skirt widths are used to approximate both the MR head microtrack profile and the written track profile. The crosstrack profile model result is compared to a measured profile and is shown to accurately reproduce its shape. A servo Position Error Signal (PES) model then is constructed from the crosstrack profile expression. Deviations from PES linearity and gain variations due to MR element microtrack shape variations are studied using the PES model.

Bias study on seed-layered DSMR head

Bias profile of a DSMR head with conductive seed layers is studied by utilizing a transmission-line model. A closed-form analytical formula has been obtained as a function of head geometry and current shunting. It is found that if the two magnetic sensing elements are still symmetrically located between shields as before, the first MR element bias angle would be reduced while the second MR element bias angle would be increased by the same amount which is proportional to the shunting current if no saturation occurs at middle of bias profile. Studies also suggest that keeping the same total read gap length the bias angle difference is smaller when the two MR elements are designed to be closer to each other. Shifting both the two MR elements toward the top shield with a certain small distance is found to be more effective to compensate bias angle difference through introducing asymmetric image current fields.

Micro-track profiles of ESD damaged AMR and GMR heads

We systematically studied the micro-track profiles of ESD damaged AMR and spin valve GMR heads, and correlated these with the dynamic electric performances of each head. Spin valve GMR heads and two types of AMR heads made by different structure and material are ESD (HBM) stressed and studied. We observed a double peak in micro-track profile after more than 10% change of MR resistance. This means that the centers of AMR and GMR sensors become less sensitive before the total melting of MR element during ESD zapping. We also observed double peak micro-track profile after pin reversal of SV head. We attribute this to changes in the domain configuration caused by partial reversal of pinned layer moment along MR (GMR) stripe.

Regulation of the Human Na/K-ATPase β1 Gene Promoter by Mineralocorticoid and Glucocorticoid Receptors

Expression of the human Na/K-ATPase beta1 subunit is regulated by a mineralocorticoid- and glucocorticoid-responsive elements. Here we identified an MR and GR responsive element, at positions -650 to -630, within the beta1 gene promoter that is required for both MR and GR activation. Independent expression of MR and GR activated by aldosterone or triamcinolone acetonide (TA) leads to significant transactivation of the beta1 promoter. Yet coexpression of both receptors activated by aldosterone plus TA or cortisol results in a much lower induction, indicating that coexpression of MR and GR is inhibitory. Gel shift mobility assay using an oligonucleotide including the 21-base pair MRE/GRE with whole cell extracts prepared from CV-1 cells overexpressing MR or GR showed specific MR and GR binding to this sequence. Additionally, antibodies to both MR and GR effectively supershifted the protein-DNA complexes, indicating that these receptors bound to the DNA sequence. Finally, the 21-base pair MRE/GRE was capable of activating transcription from a heterologous promoter in response to both aldosterone and TA. Together these data indicate that the 21-base pair sequence represents a true MRE/GRE and that optimal activation of the human Na/K-ATPase beta1 promoter is controlled by mineralocorticoid and glucocorticoid hormones. It appears that an interaction of MR with GR on the beta1 promoter effectively down-regulates transcription.

Thin-film heads with anisotropy-determined track widths

Multitrack yoke-type MR readout heads having a single shared front fluxguide with a highly anisotropic permeability, have been designed and evaluated. The well defined microtrack response profiles of these heads show that the anisotropy of the permeability confines the flux-detection to the area on tape in between the contact leads of the MR element. This can be exploited in "full-density" tape recording heads which read directly a number of adjacent tracks.

Off-track response versus shield width at the ABS for MR heads

The shield width of an MR head is an important factor in the off-track performance of the head. The shields reduce the off-track magnetoresistive pickup of the MR element, however, the inductive response of the shields is a source of off-track coherent noise which can be detrimental to disk drive performance. In this study, the off-track magnetoresistive response is modeled for heads with varying shield widths at the ABS. Using Focused-Ion-Beam processing, heads of varying shield widths were fabricated and compared to the model. The minimum shield width was determined to be six gap lengths wider than the MR element.

MR Response Stability on Geometry for an Abutted Junction of the MR Element and Longitudinal Bias Layer

Hysteresis and baseline shift are studied in soft-adjacent-layer-biased MR sensors with abutted quasi-permanent magnetic bias. The magnet consists of NiFe/NiMn exchange-coupling films, which apply longitudinal bias field to an MR sensor. Abutted bias-magnet structures with various taper angles fabricated, and the overlap lengths were measured as the length of the MR flat active region covered by the longitudinal bias films. The hysteresis measured from the transfer curve decreases with decreasing overlap length. The repeatable baseline shift in the readback signal was also improved by decreasing the overlap length in the MR sensor.

The influence of domain activities on MR head performance

The relation of signal distortion of MR heads to the domain structure and the domain activities was studied in this paper. Several kinds of MR elements were fabricated and a measurement system was set up to measure magnetoresistivity. A large drop near the peak of the output wave form was found for some MR elements. And the magnetic structure of the MR element was investigated by the ‘‘Bitter pattern.’’ It was seen that there existed multidomain in the part of the lead without gold coating. Furthermore, it was also found that the multidomain existed in the junction of leads and the MR element, and the new domain looked like a hook. The appearance of this hook-shaped multidomain has not been reported up to now in literature. The design of the MR element was modified to eliminate the drop in the output wave form and the drop was reduced substantially. Our study shows that suitable geometric dimensions and structures of leads are also very important to high performance of MR head in head design in addition to select the optimum biasing conditions.

ＭＲ素子の感度分布に及ぼすＳＡＬ膜の影響の数値解析

The sensitivity profiles optimum bias field and transverse transfer curves of MR elements biased by a soft adjacent layer (SAL) were analyzed by using micromagnetic calculations. Four MR element structures, with different SAL magnetization configurations in the wing regions, were investigated. Additional peaks appeared at the base of the sensitivity profile when the elements had a SAL side wing capable of propagating the signal flux from the recording medium. The sensitivity increased and the optimum bias field decreased as the effective anisotropy field of the MR film was decreased by the MR element structures. When the MR element without a SAL side wing was under-biased, a hystersis arose in the MR response to a cycle of a transverse external field.

The role of conductor geometry in the stable performance of SAL biased MR heads

The magnetic domain stability of SAL biased MR heads is intimately related to the current flow pattern in the MR active element. This is significantly affected by the conductor geometry near the active area of the MR element. This effect was demonstrated by studying the magnetic stability of two different conductor geometries on a quasistatic tester. A significant improvement in the stability was shown by modifying the conductor geometry to allow a uniform current flow pattern in the MR layer.

Comparative study of MR head designs with abutted vs. overlaid permanent magnet bias

We have developed Soft-Adjacent-Layer (SAL)-biased MR head products with two types of permanent magnet (PM) domain stabilization schemes, namely, abutted and overlaid. Both types of MR heads are capable of achieving recording density of 500 Mb/in/sup 2/ with linear bit densities ranging from 100-118 kbpi. While transfer curves with a transverse sweeping field showed similar behavior for both PM schemes, the overlaid structure has a large hysteresis in its transfer curve under a longitudinal sweeping field while the abutted junction was hysteresis free. Micromagnetic modeling showed that the hysteresis for the overlaid scheme arises from the varying field response of the MR element in the active region, under the leads and under the PM. Magnetic test shows that the abutted MR head with a PM defined TW had a slower rise in sensitivity and had an effectively narrower magnetic track width. On the other hand, the overlaid MR head with an active region defined by the leads with MR under them has a steeper rise in sensitivity, a broadened magnetic read track and side readings.

Narrow track MR head technology

Narrow track technologies for shielded MR heads are discussed in terms of off-track performance and increased head output. Permanent magnet bias heads are increasingly superior to exchange coupling bias heads as tracks become narrower, because of the excellent off-track performance of the permanent magnet type. Increasing the sense current is one way to increase head output. However, the current increase raises the temperature of the MR element and degrades performance. An analysis of the thermal behavior of the shielded MR head shows that increasing the thermal conduction of the shield and gap layers, which are the main sources of heat radiation, and improving the crystalline properties of the Ni-Fe film effectively suppress the rise in temperature of the MR element.

磁気的分離膜を表面酸化で形成した３層ＭＲ素子

A surface oxidation layer of amorphous Co-Zr-Mo bias film was applied to a 10Å magnetic separation film in a trilayered MR element. Because the surface oxidation layer was thinner than the sputtered film, the bias field saturated at a smaller sense current and the saturation bias field became larger. This paper discusses the state of the surface oxidation. the application of a surface oxidation method to a crystal bias film, and the effect of the process temperature. Oxygen is located at an interatomic position without forming oxide, and a high-density-oxygen area in the bias film becomes nonmagnetism. The surface oxidation method can be applied to both amorphous and crystal bias films. A study of the effect of heat showed that the trilayered MR element is stable at process temperatures up to 240°C.

ローレンツ電子顕微鏡法によるＭＲ素子の磁区観察

Magnetic domain structure change under a magnetic field across the length of an MR element (transverse magnetization) was observed in detail by Lorentz electron microscopy for a sample whose size was the same as that of the actual element, l0 × 100 μm2. Various magnetic field were applied through the objective lens of the electron microscope utilized. During the magnetization process, the element retained a single magnetic domain structure while non-uniform rotation of the magnetization took place within the domain. The transfomation from the nonuniform to uniform rotation of the magnetization upon the application of a longitudinal bias field was confirmed.