Giant Magnetoresistive Heads Research Articles

Large magnetoresistance in Heusler alloy-based current perpendicular to plane giant magnetoresistance sensors

Increasing the data storage in next-generation hard disk drives requires a reduction in the physical dimensions of read sensors. Tunneling magnetoresistance heads yield high magnetoresistance (MR) ratio but with a high resistance-area product (RA) that is suboptimal for devices. Giant magnetoresistance (GMR) head using different materials is an alternative way to improve reader performance with high MR ratio and low RA. In this paper, we theoretically study the effect of material properties and the layer thickness on RA and MR ratio in a trilayer system via an atomistic model combined with the spin transport model. The GMR stack can be constructed by the atomistic model and the RA and MR ratio can be directly calculated by considering the spin accumulation and spin current from the spin transport model. It is found that the spin valve using the Heusler alloy electrode with high spin polarization exhibits a high MR ratio and RA of 64 which is better than the spin valves using conventional ferromagnets such as Co, NiFe and CoFe. Moreover, we consider the thickness dependence of the change of RA (). Increasing the free layer thickness yields the increase in and MR ratio because of the enhancement of the bulk spin scattering. Additionally, the results show that the depends on the spin diffusion length of the nonmagnetic materials (). The increases from 3 up to 10 when increases from 35 to 1200 nm. This investigation shows the possibility for read head design of HDDs with areal density beyond 2 Tb in−2.

対向面積の異なる金属筐体から帯電物体を遠ざけたときに生じる静電誘導電圧

A sensitive device, for example, a giant magnetoresistive head contained in an electronic equipment, often malfunctions because of the induced voltage of less than 10V when a charged human body is present near the equipment. Such accidents due to electrostatic induction occur when the charged body moves. The author focuses on the induced voltage of opposite polarity generated on the metal box when the charged body moves away from the box. In experiments, metal boxes of different heights are used to change the facing area between the charged body and the box. In addition, the position of the metal box is changed so that the induced voltages of the box can be compared. The results show that the induced voltages and the electric charges increase as the facing area between the metal box and the charged body increases. The induced voltage of the metal box indicates the value of approximately -370% of the charged body when the facing area between the metal box and the charged body increases. Further, the induced voltages and the charges are slightly dependent of the position of the metal box. The results will be useful for the design of electronic equipment from the standpoint of preventing malfunction and failure of the equipment.

Development of advanced barium ferrite tape media

We developed an advanced particulate magnetic tape using fine barium ferrite (BaFe) particles for magnetic-tape storage systems. The new tape showed a signal-to-noise ratio (SNR) that was 3.5dB higher than that of the commercially available BaFe tape used for the Linear Tape Open generation 6 tape-storage system, at a linear density of 300kfci measured with a giant magnetoresistive head with a reader width of 0.45µm. Such significant increase in SNR was achieved by reducing the magnetic particle volume from 1950 to 1350nm3, while maintaining a sufficiently high thermal stability, improving the perpendicular squareness ratio from 0.66 to 0.83, and improving the surface roughness from 2.5 to 2.0nm when measured by atomic force microscopy and from 2.4 to 0.9nm when measured by optical interferometry. This paper describes the characteristics of the new BaFe particles and media, which are expected to be employed for future high-capacity linear-tape systems.

Effect of Thermal Conditions on Bit Error Rate for Barium-Ferrite Particulate Media

In this study, the thermal stability of user data written on perpendicularly oriented barium-ferrite media was evaluated in terms of the bit error rate. To determine whether recorded data can be read back after long-term preservation, we recorded a pseudorandom data pattern on barium-ferrite media at a linear density of 500 kbpi and baked the media at 65°C for an extended period. After baking, the recorded data were read back using a 0.45m-wide giant magnetoresistive read head. The bit error rate was calculated using the GPR4ML-AR model. It was found that the bit error rate was stable even after one year at 65°C. This result indicates that perpendicularly oriented barium-ferrite media has high thermal stability.

Characterization of Contact Discharge Between Small-Capacitance Devices

The giant-magnetoresistive head suffers magnetic damage from electrostatic discharge (ESD) current on the order of 10 mA and thermal damage from ESD energy on the order of 0.5 nJ. The discharge between 2-pF capacitors at 10 V gave a peak current of 34 mA, and the discharge between 100-pF capacitors at 100 V reached 1.5 A. The peak current arose on the order of picofarads and was approximately maximized at the same value of both capacitors. Theoretical energy loss was estimated by the difference between the potential energies prior to and following the discharges. The energy loss was 0.05 nJ for 2-pF capacitors at 10 V and increased in excess of 0.5 nJ for greater than 20-pF capacitors. Therefore, the discharge between picofarad capacitances tends to cause the magnetic damage, and increasing the capacitance causes the thermal damage. Comparison of the potential energy loss and the current energy derived that the contact resistance varied from more than 200 to few ohms as the voltage and the energy loss increased.

ハードディスクドライブ用磁気記録ヘッドにおける磁化挙動解析手法の実際と将来展望

With the increase in the recording density of hard disk drives, the narrower magnetic pole and read-sensor widths in writing and reading heads are required, and techniques used for the magnetic behavior analysis in a nanoscale area is essential. The observation of the in-plane domain structure of the writer pole for a perpendicular recording (PMR) head was performed by electron holography in order to elucidate the mechanism of the pole erasure originating from the instability of the magnetic domain state. The results revealed that the stability of the domain structure is strongly related to the domain wall trapping, and the pole erasure can be suppressed by realizing the stable domain structures. With respect to a current perpendicular to plane (CPP)-giant magneto-resistive (GMR) head, which has been promising candidates of a next-generation reading head element, the insertion of non-magnetic materials, such as Cu, between the ferromagnetic pinned and free layers is known to increase the MR ratio. For realizing the practical use of the CPP-GMR head, effects of the insertion of materials on the increase in the MR ratio were investigated by X-ray magnetic circular dichroism (XMCD). The results revealed that XMCD is a powerful technique to obtain information on electronic states and magnetic moments with the help of the theoretical electronic band calculation. The potential application of secondary cantilever resonance magnetic force microscopy and spin-polarized scanning electron microscope to the in-situ magnetic imaging of PMR heads will be also discussed.

Spin-Torque Effect on Thermally Excited Magnetization Fluctuation Noise in Tunneling Magnetoresistive Read Heads

The spin-torque (ST) effect on the thermally excited magnetization fluctuation noise (thermal mag-noise) in tunneling magnetoresistive (TMR) read heads is investigated in the GHz range using noise spectra. The strong noise spectral peak around 3.1 GHz is attributed to thermal mag-noise originating from the free layer. The peak intensity and linewidth strongly depend on both the external magnetic field and current density. These features demonstrate that the ST effect significantly influences the thermal mag-noise as the current density increases up to the critical current density. Additionally, it is speculated that the non-thermal fluctuation noise originating from ST in the TMR heads as well as in current perpendicular to plane giant magnetoresistive (CPP-GMR) heads is generated above a critical current of approximately 2.5×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sup> A/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Modeling of contact discharge between floating devices

The Giant-magnetoresistive (GMR) head suffers magnetic damage from ESD current on the order of 10 mA and thermal damage from ESD energy on the order of 0.5nJ. Contact discharge from an electrified object into a floating device was investigated as the peak current caused magnetic damage and as the energy-loss caused thermal damage. Experiments with discharges between various capacitors clarified that the discharge between 2pF-capacitors at 10V gave a peak current of 34mA and the discharge between 100pF-capacitors at 100V reached 1.5A. A 2D-plot of the peak current simulated by PSPICE indicated that the peak value arose at the order of pF and was approximately maximized at the same value of both capacitors. Theoretical energy-loss was estimated by the difference between the potential energies prior to and following the discharges. The energy-loss was 0.05nJ for 2pF-capacitors at 10V and increased in excess of 0.5nJ when both capacitors were grater than 20pF. The energy-loss reached 250nJ for 100pF-capacitors at 100V. 2D-plot of the energy-loss indicated a gradual increase as both capacitance-values increased. In order to decrease the risk of ESD failure, reducing the capacitance of the device was effective, because the transferred-charge and energy-loss were restricted.

Study on ESD Phenomena of Magnetic Head by 1ns Pulse ESD

Magnetic Recording heads, the most electrostatic discharge (ESD/EOS) sensitive device of all electric devices, are used for high density magnetic recording applications. Recently, as the devices become increasingly smaller, there has arisen a concern for damaging GMR (Giant Magneto Resistive) heads by EMI. Also, CDM or nano second pulse ESD is key issue for Magnetic head manufacturing. In order to study the effect of ESD (Electro Static Discharge) with nano pulse width for GMR heads, transfer curves of GMR heads using high field QST (Quasi Static Tester) were investigated. By applying ESD damage to GMR head, the transfer curves change the waveforms. Also, there are many kinds of waveforms of transfer curves for after ESD damaged heads. It was found that the degradation of pinned layer was caused by nano pulse ESD and the phenomena were detected by high field QST.

Special Section Guest Editorial: Nanoengineering: Fabrication, Properties, Optics, and Devices

Nanoengineering is the controlled placement or removal of material on the atomic, molecular, or small granular scale. The term has typically encompassed the engineering of materials at dimensions of 100 nm or less. The beginning of nanoscience, or nanoengineering, is not really clear. Metallurgists and glass formers have been making specially engineered sintered and nanocrystalline materials for many decades. Chemists have also synthesized molecular clusters and enzymes for many years. Watson and Crick proposed molecular templating in “Molecular structure of nucleic acids: a structure for deoxyribose nucleic acid” (Nature, 1953). However the emergence of the fields of nanoscience and nanoengineering is widely attributed to the famous speech by Richard Feymann, “There is plenty of room at the bottom,” given at the American Physical Society Meeting, December 29, 1959. The growth and blossoming of the nanoengineering field over the past 50 years has indeed proved that there is plenty of room at the bottom. Engineered two-dimensional nanostructures have become part of our everyday life, such as the CMOS chips in our electronic devices, the high-mobility transistors in our cell phones, and giant tunneling magnetoresistive heads for the disk drive in our computer and digital video recorders. In order to make products ever more widely used and low cost, nanoengineering in all three dimensions has become critical to many applications. Mature technologies such as logic, memory, and data storage have been rapidly thrust into the sub-100-nm regime. Existing processes of record have been extended well beyond the ranges deemed feasible or reliable. New technologies such as sensors, systems on a chip, biotechnology, photonics, photovoltaics, molecular electronics, and optics are emerging. The upcoming synthesized nanomaterials, nanotubes, and nanowires, offer extremely attractive physical features and great opportunities. Continuing improvements in the design and fabrication of miniature optical elements have driven the development of micro/nano/quantum-scale optical and optoelectronic elements in ever more diverse applications. Application areas include telecommunications, data communications, consumer electronics, microwave photonics, optical computing, neural networks, optical storage, information display, optical imaging, printing, optical sensing, optical scanning, renewable energy harvest and storage, medical diagnosis, and chemical/biological sensing. The upcoming nanotechnologies present new opportunities and challenges in materials processing, device design, and integration. Drivers for commercial deployment include functionality, space, performance, reliability, and cost, as well as energy independence and climate change mitigation. The papers in this special section show some of the novel applications of nanoengineering. Manyofthematuretechnologiesextendexistingpatterningprocessesofrecord,suchaslithography and etching—a top-down patterning approach. The papers here illustrate both new methods and applications of nanoengineering. Some of the applications are best served by a bottom-up, self-organization, or templated growth approach to material control. “Optical characterization of silicon-on-insulator based single and coupled racetrack resonators,” by Mattia Mancinelli et al., shows the use of nanoengineering to make conventional semiconductor electronics faster

ESD Tolerance of GMR and TMR Heads Within Hard Disk Drives

Electrostatic discharge (ESD) tolerance is discussed for giant magnetoresistive (GMR) and tunneling magnetoresistive (TMR) heads within hard disk drives (HDDs). There are two kinds of testing methods for ESD: the component ESD method with Human Body Model or Machine Model and the IEC61000-4-2 testing method. The IEC61000-4-2 testing method for GMR and TMR heads within head gimbal assembly (HGA), head stack assembly (HSA), and HDD was surveyed first, and the ESD tolerance at each state of HGA, HSA, and HDD was evaluated. The equivalent circuits for three states were proposed and proved to be consistent with experimental results by the IEC61000-4-2 testing method.

Dissipative Gap Material in Tape Heads

A giant magnetoresistive (GMR) head in tape-recording systems is affected by the electrostatic discharge (ESD) between the sensor and magnetic shields. Hence, Pt-doped Al2O3 was developed as a dissipative gap material to reduce the ESD current. Pt chips were sputtered on an alumina target to vary the film resistance. The decay time of a charged plate on Pt-doped Al2O3 was measured for various film thicknesses. The I-V characteristics indicated that, as the applied voltage increased, the Pt-doped Al2O3 film increased the current gradually, whereas the Al2O3 film increased the current rapidly over the breakdown voltage.

High Recording Density Tape Using Fine Barium-Ferrite Particles With Improved Thermal Stability

The effects of reducing barium-ferrite magnetic particle volume have been studied. We optimized barium-ferrite substitution elements and their amount and demonstrated thermal stability for very fine particles of the size 1.5 × 103 nm3. Using a giant magnetoresistive (GMR) head with a 0.2 ?m read track width, test tape containing these fine particles exhibited a bit error rate of 1.5 ×10-4 at a linear density of 360 kbpi using a noise predictive maximum likelihood (NPML) detection for nonstationary noise sources, i.e., data-dependent noise. This corresponds to a 15 Gb/in2 areal recording density in linear tape application.

Analysis of Spin-Torque Noise in a CPP-GMR Head

Technologies for realizing areal recording densities of over 1 Tbit/inch2 in hard disk drives have been aggressively developed. At such high densities, it is necessary that a read head should be able to sense a weak magnetic field straying from a recorded medium. One of the most promising candidates for such a head is a current-perpendicular-to-plane giant magnetoresistive (CPP-GMR) head. However, it has been pointed out that in a CPP-GMR head, injection of polarized spin into a free layer causes spin-torque noise, which is peculiar to CPP-GMR heads. Several experimental and theoretical results on spin-torque noise have been reported. Thus, it is necessary to investigate the relationships of spin-torque noise with various parameters of a CPP-GMR head. In this paper, the dependencies of the spin-torque noise power and spectrum on the amplitude of the sense current density, its polarity, and the amplitude of the exchange interaction acting on the pinned layer are investigated by means of micromagnetic simulation. As a result, it is clarified that the noise properties are strongly influenced by the polarity of the injected spin, and that the noise power spectrum is located in narrow regions of frequency space.

Micromagnetic Simulation of Transfer Curve in Giant-Magnetoresistive Head

The transfer curve of the giant-magnetoresistive (GMR) magnetic head represents its most important property in applications, and it is calculated by the micromagnetic modeling of the free layer and the pinned layer in the heart of the GMR head. Affections of the bias hard magnetic layer and the anti-ferromagnetic pinning layer are modeled by effective magnetic fields. The simulated transfer curve agrees with experiment quite well, therefore the values of these effective magnetic fields can be determined by the model. A synthetic antiferromagnetic spin valve structure GMB. head is also analyzed for comparison.

Magnetic Spacing Trends: From LMR to PMR and Beyond

This paper examines trends in magnetic spacing in the hard disk drive industry for the last 15 years or so, as we transitioned from inductive to magnetoresistive (MR), giant magnetoresistive (GMR), and tunneling magnetoresistive (TMR) heads, and from longitudinal to perpendicular recording. Historical data show surprisingly good scaling relationships between areal density, linear density, track density, bit aspect ratio (BAR), and magnetic spacing. These trends have held from below 1 Gb/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> until today's densities, with no significant discontinuities when crossing major technology changes. In particular, it is found that magnetic spacing has scaled with the length of the bit, and more specifically has equaled about half the bit length. Magnetic spacing components, on the other hand, show larger degree of deviations from the trend. Projections to 1 and 10 Tb/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> are made.

ELECTROSTATIC DISCHARGE EFFECTS ON GMR RECORDING HEADS USING A WAVELET TRANSFORM APPROACH

Electrostatic Discharge (ESD) effects have been identified as one of the most dangerous causes of giant magnetoresistive (GMR) recording head damage. These phenomena have been studied at all levels of hard-disk drive manufacturing 1. The head gimbal assembly (HGA) is mainly studied because of its exposure to the environment. The standard models are typically based on the human body model (HBM), the machine model (MM) and the charged device model (CDM) where research and practical tests are incompatible. In production, one or more ESD models are normally effective while the other is undergone under a separate model. In addition, tests in the time domain are more accurate than those in the frequency domain. However, picosecond measurements are taken with difficulty where the frequency domain measurement provides non-real time results. Therefore, this is the first report of serial ESD detection using the new technique of wavelet transform. It has been found that the glitch occurs when the ESD level of HBM – MM and HBM – CDM serial ESD on GMR heads are in the ranges of 1.2-2.6 V and 12-15 V respectively.

Evaluation of GMR Head Durability against Nanoscale Scratches Using High-Field Transfer Curves

We investigated the durability of giant magnetoresistive (GMR) heads to nanoscale scratches created during the lapping process. Analysis using high-field transfer curves after deliberate scratching with an atomic force microscope (AFM) identified changes in the magnetization of the head and a reduction in pinning strength, which is a magnetic performance indicator. Additionally, finite element method (FEM) analysis suggested that the overall effects on the GMR head following nanoscale scratching increased with scratch depth.

ESD Affected GMR Head Detection by Using Machine Model: Wavelet Transform Technique Approach

This report proposes the wavelet transform technique using the 4th Daubechies order to detect glitches on a magnetic recording head signal in the time-domain. It is found that the glitch occurs when the electrostatic discharged (ESD) level of the machine model (MM) on giant magnetoresistive (GMR) heads is in the range of 6-9 V. The electrical test parameter and scanning electron microscope (SEM) photograph of recording heads shows no change in reader sensor. However, the parameter and SEM results clearly show the visible GMR damage when the MM-ESD voltage (VESD) is 10 V. The glitch in magnetic response signal of the GMR head occurs when the VESD is increased. Therefore, the wavelet transform technique can be a novel instrument to forecast the GMR degradation due to the MM-ESD effect.

Investigation of fabrication and hetero-epitaxy relationship of CoCrPt thin films grown on CrW underlayer

This paper reports that longitudinally oriented CoCrPt thin films with Cr85W15 underlayer and CoCr intermediate layer for use of giant magnetoresistance heads were fabricated by magnetron sputtering. Without CoCr intermediate layer, CoCrPt layer deposited directly on Cr85W15 underlayer which has a dominant (200) texture exhibits unexpected (101̄1) texture. After introducing CoCr intermediate layer, the CoCrPt layer shifts into (112̄0) texture. This article studies the crystallographic hetero-epitaxy relationship between magnetic layer and underlayer in order to understand the appearance of CoCrPt (101̄1) texture on (200) textured Cr underlayer and the influence of CoCr intermediate layer on the inducement of CoCrPt (112̄0) texture. The CoCr intermediate layer plays a crucial role in controlling the microstructure and consequently the magnetic properties of the overlying magnetic layer.