Spin-valve Heads Research Articles

Narrow-track antisymmetric dual magnetoresistive head performance on rigid media

In this work, the performance of an antisymmetric dual magnetoresistive (A-DMR) head, having a track-width of W/sub t/=2 /spl mu/m, a stripe height of h=2 /spl mu/m and a gap length of 80 nm, is presented and compared to theory. A thin film inductive head that incorporates high magnetization FeAlN poles, with a gap length of 0.25 /spl mu/m, was used to record thin film disk media with an areal magnetic moment of 0.5 memu/cm/sup 2/ and a coercivity of 3 kOe. The A-DMR roll-off and spectral curves that are fit in amplitude and shape with a 2-D analytical curve, indicated D50=190 kfci. The theoretical curves fit the experimental data with two fitting parameters, the spacing parameter of the spacing loss term and a parameter /spl zeta/=/spl zeta/ (W/sub t//h) that can be calculated with a 3-D micromagnetic model. The cross-track profile, off-track response and adjacent track interference are analyzed in the time domain and compared with previously reported theoretical results, where in this case the write head track-width is 2.5 /spl mu/m. The head showed some adjacent track interference and pulse amplitude asymmetry at lower linear densities, mainly due to a lower magnetic transverse bias level of one of the sensor layers. In spite of the good linear resolution of these heads, they offer limited sensitivity in comparison to spin valve heads.

Write induced instability in spin-valve heads

The output amplitude variation of a spin-valve (SV) head, induced by a write operation, was investigated. The characteristics well depended on the sign of the write current just before a readback process started. It indicated that the write-induced instability should come from a magnetization hysteresis of somewhere magnetic materials. The magnetic core, which consisted of shields and a yoke, was under suspicion as a candidate of the hysteretic origin by sense current, medium and external field excitation tests. Magnetization modeling of a head core revealed a possible mechanism of the instability, which was a shield-related hysteresis.

Design and modelling of dual spin-valve heads

Two types of dual spin-valve head structure, the anti-parallel and parallel dual spin-valve heads, were proposed. Both dual spin-valve heads are thermal noise immune due to differential voltage sensing. The transfer functions of the two dual structures were analysed and transfer curves of shielded heads were simulated using a 3-D finite element method. Results have shown that the anti-parallel dual spin-valve head exhibits greater linear dynamic range than a single spin-valve head and almost doubled output of a single spin-valve head. It also has an ideal transfer curve passing through the origin independent of the bias state of single spin-valves.

ＥＳＤによるスピンバルブヘッドのピン層磁化反転過程

We measured the micro-track profiles of spin-valve heads after damage by ESD. The output was reduced and the profiles showed several peaks depending on the ESD voltage. We proposed two models for the magnetization reversal process of the pinned layer in the spin-valve heads, and calculated the micro-track profiles by using 3D micro-magnetic simulation. In the first model, the pinned layer magnetization is gradually rotated as the ESD voltage is increased. In the second model, the direction of the pinned layer magnetization is reversed in the center of the spin-valve element and the reversal region width is increased as the ESD voltage is increased. The calculation results for the second model agreed fairly well with the experimental results. We think that at first the pinned layer magnetization is locally reversed in the center of the element after ESD in the spin-valve head.

Noise and magnetic domain fluctuations in spin-valve GMR heads

Random telegraph noise (RTN) can be observed in the voltage across some spin valve heads over particular ranges of bias current, magnetic field and temperature. The detailed dependence of the RTN signal on these parameters demonstrates that the noise is due to thermally activated magnetic domain fluctuations. Further, a comparison of the effects of applied magnetic field and bias current provides information about the physical location of the magnetic domains within the head.

Greater than 14 Gb/in/sup 2/ spin valve heads

We have designed and fabricated dual spin valve heads with synthetically pinned layers. They have excellent sensitivity. The read-back waveform has a small asymmetry and that is also insensitive to the bias current. The read gap length is of 0.14 /spl mu/m and the write gap length is of 0.2 /spl mu/m. The read heads have a nominal magnetic trackwidth of 0.5 /spl mu/m and a nominal write magnetic trackwidth of 0.8 /spl mu/m. The write heads were conventional inductive heads with their pole geometry defined by focused ion beam (FIB) technology. The dual spin valve heads have achieved an areal read/write density as high as 14.5 Gb/in/sup 2/ at a data transfer rate of 23/spl sim/24 MB/sec. The sensitivity of the readers is as high as 3.6 mVp-p//spl mu/m. The bit aspect ratio is as high as 14.

Micromagnetic simulation of 20 Gb/in/sup 2/ spin valve heads with heating effects

A micromagnetic model is described and used to study the behavior of spin valve recording heads. The finite difference method is used to solve for the magnetostatic potential, the electrostatic potential and the temperature. With this formulation we can investigate the effect of structure shapes, current distributions, and temperature on the magnetic performance of magnetoresistive read heads. Details of device response degradation due to increased resistivity is shown.

PdPtMn/CoFeB synthetic ferrimagnet spin-valve heads

We deposited spin-valve films with a CoFeB/Ru/CoFeB synthetic ferrimagnet pinned trilayer and a PdPtMn anti-ferromagnet layer and investigated their MR responses. We also fabricated spin-valve heads having a Ta(50 /spl Aring/)/NiFe(20 /spl Aring/)/CoFeB(15 /spl Aring/)/Cu(30 /spl Aring/)/CoFeB(25 /spl Aring/)/Ru(8 /spl Aring/)/ CoFeB(15 /spl Aring/)/PdPtMn(150 /spl Aring/)/Ta(60 /spl Aring/) synthetic ferrimagnet spin-valve film. We tested the read/write performance on a low noise CoCrPt-based quaternary alloy thin-film disk. A narrow, effective read track-width of less than 0.4 /spl mu/m was measured. We obtained a normalized output with respect to track-width of 2500 /spl mu/Vpp//spl mu/m. Using a EPR4ML channel with a 16/17 code and an inductive head with a track-width of 0.45 /spl mu/m, we found a bit error rate to be less than 3.45/spl times/10/sup -6/ without error correction at a data rate of 13.3 MB/s and at a linear density of 405 kBPI on the similar disk. Furthermore, from squeeze measurements, we found the track-pitch to be 0.505 /spl mu/m, which corresponds to a track density of 50.3 kTPI. As a result, we accomplished an areal density of 20.4 Gbit/in/sup 2/ with a linear density of 405 kBPI and a track density of 50.3 kTPI using PdPtMn/CoFeB synthetic ferrimagnet spin-valve heads.

Effect of permanent magnet coercivity on transfer curve of shielded spin-valve head

The edge wall, i.e., magnetization distribution near the edge of a permanent magnet with finite coercivity was studied to investigate the stability of shielded spin-valve heads. The edge wall is structured so that the self-demagnetization field inside the permanent magnet does not exceed the magnet's coercivity. 30 nm-thick CoCrPt with coercivity of 2000 Oe was sufficient to obtain a smooth transfer curve of the spin-valve head. However, if the coercivity of CoCrPt is reduced to 200 Oe or 100 Oe, a kink or Barkhausen jump will appear in the transfer curve.

スピンバルブヘッドにおける交換結合磁界の角度分散の影響

The effect of angular deviation of the exchange bias field on the read performance of spin-valve (SV) heads was investigated. The calculated output voltage showed large variation when the angular deviation of the exchange bias field was increased. For a deviation angle of around 10°, wide variation was observed in the peak asymmetry. This seems to be caused by the generation of magnetic domains in the pinned layer. It is necessary to increase the exchange bias field up 800 Oe in order to diminish the asymmetry instability. Tilting the average direction of the exchange bias field was also effective in suppressing the magnetization reversal in the pinned layer.

Current distribution effect on micro-track profiles in spin valve devices

The methodology of the micromagnetic theory for modeling micro-track profiles is discussed. Consistent results are obtained from modeling and experiments. Then, this theory is used to investigate the micro-track profile behavior in different current distributions at sensor junctions with different permanent magnet (PM) Mrt (remanent magnetization/spl times/thickness). It is found that a lower Mrt can lead to different microtrack profiles in different current distributions. With the PM Mrt there is less current distribution effect. Thus, ones could use this approach indirectly to estimate the PM field in sensors, which is of importance in spin valve head design.

スピンバルブヘッド用ＣｒＭｎＰｔ反強磁性膜の開発

スピンバルブヘッド用ＣｒＭｎＰｔ反強磁性膜の開発

Simulation study of synthetic antiferromagnetic biased spin valve heads by using semi-classical GMR theory

For amplitude asymmetry control and thermal stability control at higher areal density, synthetic spin valve is one of the key technologies. We developed a micromagnetics model for synthetic SV with semi-classical GMR theory and estimated optimum set of thicknesses of synthetic pinned layers. The ratio of two pinned layer thicknesses is around 1.5/spl sim/1.8 for good asymmetry and high ESD resistance.

スピンバルブヘッドのオフトラック特性に対する交換結合バイアス磁場の影響

The off-track performance of magnetic recording heads is a key issue in achieving high track density. In this study, the position error signal (PES) and off-track capability (OTC) were calculated for spin-valve heads. The position error became large when the direction of the exchange bias field deviated and was disordered in the pinned layer. The OTC also as increased the deviation angle of the disordered direction of the exchange bias field decreased. Therefore, an angular deviation of less than 10 degree is necessary to obtain reliable tracking.

３層の磁性膜を有するスピンバルブヘッドの数値解析

３層の磁性膜を有するスピンバルブヘッドの数値解析

Rigid disk medium for 20 Gb/in/sup 2/ recording demonstration

A longitudinal medium was developed for 20 Gb/in/sup 2/ recording. This medium has a coercivity of 3380 Oe and M/sub r//spl delta/=0.42 memu/cm/sup 2/. Modulation noise and track edge noise were well suppressed by the decrease in the activation volume. Remanent magnetization is stable; at 338 K, the coefficient of remanence reduction was -0.066 dB/decade in a reverse field of 460 Oe which corresponds to the demagnetizing field in a bit at 430 kFCI. Recording bits of 430 kfci were confirmed by MFM. The BER was 3.45/spl times/10/sup -6/ using a conventional EPR4 channel with a 16/17 code rate at 405 kBPI (430 kFCI). From squeeze measurements, the track pitch was 0.505 /spl mu/m (50.3 ktpi) including a guard band of 0.06 /spl mu/m. 20.4 Gb/in/sup 2/ recording is made possible by the combination of a narrow gap spin-valve head and a low noise medium.

Anisotropy control in fabrication process for NiMn spin-valve dual element heads

NiMn antiferromagnets with a high blocking temperature are attractive for application to the pinning layer in spin-valve heads, because a highly stable exchange coupling field is expected through their use. We have fabricated NiMn spin-valve heads having a CoZrTa bottom shield and a CoZrTa/NiFe write element, using an anisotropy control process which provides a desirable magnetization configuration in each magnetic layer. These heads showed highly stable, symmetrical, and Barkhausen noise free readback waveforms with output voltage of over 800 /spl mu/V/sub pp///spl mu/m.

Control of asymmetry of spin valve heads based on micromagnetic analysis

Relationship between the asymmetry of spin-valve heads and various parameters is revealed by systematical investigations of a micromagnetic analysis. We design spin-valve heads with a good asymmetry by canting the pinned layer. However, for spin-valve heads for high density recording over 10 Gb/in/sup 2/, a poor asymmetry caused by the degeneration of the magnetization direction of the free layer becomes a serious problem. To solve this problem, we introduce a bias compensation layer (BCL) to the spin-valve structure. We prove that BCL is very effective in controlling the asymmetry.

Spin valve heads with a corrosion resistant MnRh exchange layer

A new exchange material, Mn/sub 78/Rh/sub 22/, is described, requiring no post-deposition anneal to obtain the antiferromagnetic phase and leading to spin valve sensors with good corrosion resistance, thermal stability up to 225/spl deg/C, and good exchange coupling characteristics. Potentiodynamic polarization scans performed in a sodium sulfate electrolyte show that Mn/sub 78/Rh/sub 22/ films exhibit a good corrosion resistance, comparable to that of Ni/sub 81/Fe/sub 19/, Mn/sub 80/Ir/sub 20/, and Mn/sub 50/Ni/sub 50/ films but with higher corrosion potential. Spin valve structures prepared with this exchange material show an exchange coupling strength (J/sub ex/) of 0.19 erg/cm/sup 2/. The blocking temperature (T/sub B/) of the as-deposited spin valve coupon samples is 235/spl deg/C. Unshielded sensors with trackwidths W=4-6 /spl mu/m and height h=1-2 /spl mu/m were fabricated. The sensors show well-linearized magnetoresistance (MR) transfer curves, without hysteresis or Barkhausen noise and are thermally stable under consecutive 5 h anneals in vacuum up to 225/spl deg/C. A shielded tape head device was fabricated showing a maximum output of 1.8 mV/sub pp///spl mu/m, with potential for operating at linear densities near 100 kfci, at which a 580 /spl mu/V/sub pp///spl mu/m output is measured.

Read sensitivity in abutted-junction type spin-valve head

The sensitivity and the distribution of read heads have become more and more vital as the recording track density has increased. From the view point of the sensitivity distribution, the read performance of abutted-junction type spin-valve (SV) heads are investigated by using Landau-Lifshitz-Gilbert micromagnetic simulation. In this model, the hard magnet film is set up at a slant to be abutted with the SV sensor edge. A long overlap length introduces negative longitudinal field. This inadequate field distribution causes the magnetization array to be disordered and irreversible magnetization changes in the free layer of the head. We also investigated the relationship between the magnetization state and the micro-track profile, as a function of sense current direction and track width. As a result, it is confirmed that the micro-track profile can be explained by the magnetization state of the free layer.