Soft Adjacent Layer Research Articles

Comparison of MR and GMR spin-valve heads for magnetic recording on MP tape

Summary form only given. The use of the giant magnetoresistive (GMR) spin valve (SV) sensor is now pervasive in production disk drives. However, the use of spin valves in tape remains noticeably absent. This is predominantly because the media properties and areal densities currently used in tape are considerably different to those in disk. The tape media thickness and thus moment-thickness product (M/sub r//spl delta/) dominates the recording in tape. The large flux levels emanating from the longer wavelength recordings in RLL recording codes drive the recording method (write equalization) and the read head design characteristics. MR sensors in the form of soft adjacent layer (SAL) biased devices and dual stripe (DSMR) structures are presently used in production tape systems, which together with write equalization give high signal amplitudes at short wavelengths with little or no element saturation at long wavelengths. Another difference between tape and disk systems is the multi-channel read-while-write function giving the unwanted parasitic feedthrough (or cross-feed) noise. It is tape specific noise sources such as this that drive the need for more raw signal amplitude off the tape even though the areal density of present and future tape systems does not approach that of current disk systems. The paper compares a 20 /spl mu/m wide DSMR head with a 4 /spl mu/m wide spin valve similar to that used in disk systems for tape applications.

Development of an integrated magnetic sensor with linear output based on spin valves

The particular objective in this article is to develop a sensor with high sensitivity and linear output that crosses zero at zero field. The sensor is an integrated magnetic device based on a Wheatstone bridge of micropatterned spin valve resistors with the addition of a soft magnetic structure that determines the principal characteristics of the sensor. This magnetic structure is a soft layer shaped to guide the magnetic flux lines of the external magnetic field to the proximity of the bridge elements with the desired angle. With this configuration we change the local field direction rather than the local anisotropy of the spin valve material in order to set up the bridge. The sensitivity of the sensor strongly depends on the permeability of the soft adjacent layer, hence it is significantly increased even in a nonoptimized device, considering other magnetoresistance devices currently available. The sensitivity reported for this device is ∼0.2 %/μT.

SAL-biased MR heads stabilized by canted permanent magnets

The design and fabrication of anisotropic magnetoresistance (AMR) heads biased with a soft-adjacent layer (SAL), stabilized by canted permanent magnet (PM), have been investigated. MR linear response to AC writer current was observed. The response of bias point to DC writer current in overlaid head stronger than abutted head indicates that this MR response to writer is at two side-wings in overlaid head while at the track edges in abutted head. This MR response to writer current can be minimized for narrow track recording by adjusting magnetization angle and strength of PM, which is confirmed by full track scan and micro-track profiles.

Effect of stress induced anisotropy on SAL-biased MR head performance

The effect of magnetostriction (MS) on the device characteristics of soft-adjacent-layer (SAL) biased magnetoresistive (MR) head was investigated. As MS changes from -7/spl times/10/sup -7/ to 1.77/spl times/10/sup -6/, the magnetic track width increases from 1.26 to 1.83 /spl mu/m. Asymmetry of bias point, output sensitivity, and output amplitude are also affected by the stress induced anisotropy. The variation of magnetostriction (/spl Delta//spl lambda/=2/spl times/10/sup -6/) induces the change in bias field by 60 Oe associated with the estimated stress of +800 MPa on the MR stripe.

Crossfeed response of DMR vs. SAL multi-track heads

A new concept of Dual Magnetoresistive reproductive mode is applied to improve the design and operation of high-performance multi-track Read-While-Write (RWW) heads for tape and/or potential disk applications. RWW operation exists in some magnetic recording units in which verifying what was recorded is necessary. A new multi-track Inductive/Dual Magnetoresistive (DMR) head design is found to reduce the crossfeed noise radiation by about a factor of 20, compared with the conventional Soft-Adjacent-Layer (SAL) Magnetoresistive Heads design, which is the most favoured approach for achieving simultaneous read and write operations, especially in a multi-track head with ultra-narrow trackwidth. To verify these analysis results, measurements with 2.9 /spl mu/m track width inductive/MR and inductive/DMR heads were done.

Increased field sensitivity in Co/Cu multilayers with soft adjacent layers

The use of simple magnetic multilayers such as Co/Cu in high-sensitivity magnetic devices is limited by the high saturation field required to achieve the maximum GMR. Most GMR devices currently use spin-valve structures which exhibit significantly smaller GMR values but have a much lower saturation field, and hence a higher sensitivity. We have demonstrated a GMR device based on Co/Cu with an integrated soft adjacent layer (SAL) structure to enhance the low field sensitivity to 60% mT/sup -1/ in applied fields of appropriate orientation below 1 mT. This high sensitivity to small magnetic fields and their direction makes devices of this type well suited for a variety of applications.

Instability analysis of SAL-biased magnetoresistive heads using rotational applied field

Magnetoresistive (MR) head achieves high areal density in a magnetic recording system due to high sensitivity of the magnetic field. The high sensitivity of MR sensor, however, potentially causes an instability of readback signals. This instability appears as a variation of the output wave form during alternating reading and writing processes. In this study, MR heads were measured by a new technique that used rotational applied field. This technique is intended for checking the stability of magnetic domains against the arbitrary direction of the magnetic field. As a result, deviations of transfer curves for the MR sensor correlated to variations of the output voltage. This deviation seems to be caused by the Barkhausen jump in MR sensors. In order to analyze the Barkhausen jump, a simulation using the Landau–Lifshitz–Gilbert (LLG) equation was carried out. A calculated transfer curve of the MR sensor was similar to a measured curve, and it included two different origins of the Barkhausen jump. The first type of jump happened in the MR film. A rotational applied field generated domain walls in the active region of the MR film. The second type of jump occurred in the soft adjacent layer (SAL) film. The appearance of vortex domain walls changed the bias field from the SAL film, and then it forced a bias state variation in the MR film. The first type and second type of Barkhausen jump showed 0.05 and 0.01 Ω resistance change, respectively. But, in reducing the MR sensor height, the Barkhausen jump was suppressed, even in the case of a small domain stabilizing bias field.

Sensitivity analysis of structure in GMR/insulator/SAL sensor

A guideline for the optimum design of the soft adjacent layer (SAL)-biased giant magnetoresistive (GMR) sensors, which are a promising MR head for use at high areal densities, with electromagnetic field computation based on a 2D finite element method is reported. The bias level is highly sensitive to the element height, and it is desirable that element height should be less than 1 /spl mu/m for the shielded sensor.

Effect of MR read non-linearities on extracted dipulse response

The effect of MR nonlinearities on the extracted dipulse method has been studied. The study shows that there is a strong relationship between MR nonlinearities arising from soft adjacent layer (SAL) thickness or MR bias current variation and measured nonlinear transition shift echo amplitude (NLTS). A formation of a new echo is observed in the extracted dipulse spectrum in the case of high MR nonlinearities.

Stress induced anisotropy effect for SAL films in magnetoresistive elements

The stress configuration of SAL (soft adjacent layer)-biased magnetoresistive (MR) elements has been analyzed, in order to study the stress-induced anisotropy effect on the MR transfer characteristics. The stress analysis, on the basis of stress measurement results in the single-layer sheet films that formed the MR elements, shows that anisotropic tensile stress of around 100 to 300 MPa is induced in the element height direction in the SAL film with an open-pattern edge structure. Furthermore, we calculated the MR transfer curves using a micromagnetic model for samples with different saturation magnetostriction constant (/spl lambda//sub s/) value for SAL films. Assuming anisotropic tensile stress of 300 MPa in the element height direction throughout the entire track region, a desirable /spl lambda//sub s/ value for SAL films is in the range from +1/spl times/10/sup -6/ to -2/spl times/10/sup -6/, because the stress-induced anisotropy in the SAL does not seriously affect the /spl mu/R transfer curves.

Recording limitations for SAL/MR and dual-stripe heads

A micromagnetic modeling analysis is performed to investigate the areal recording density limitations of the soft adjacent layer (SAL) biased and dual-stripe (DS) magnetoresistive recording head structures. The simulation analysis yielded four principle results: First, the higher output advantage of the DSMR head structure over the SAL head structure is largely due to the ohmic shunting loss of the SAL layer in the present SAL heads. Second, both the SAL and DSMR head structures are capable of supporting read track width as narrow as W=0.5 /spl mu/m. Third, in order to support high linear densities, the spacing between the two MR stripes in the DSMR structure must be narrowed to obtain the adequate spectral response. There is, however, a corresponding amplitude reduction that is due to the magnetostatic interaction between the two stripes. Fourth, the track width broadening inherent in the DSMR structure when the two MR films are misaligned can be eliminated with a sense current inversion.

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.

Sputtered NiFeZr as a soft biasing layer in MR head

The sputtered soft magnetic NiFeZr films were studied experimentally for the use as a soft adjacent layer (SAL) in magnetoresistive (MR) heads. The influence of the film thickness and sputtering conditions on the magnetic and electrical properties of the films was investigated. The coercivity H/sub C/ and the anisotropy field H/sub K/ considerably depends on the substrate temperature T/sub S/ during the deposition. The films of the thickness below 400 /spl Aring/ have the following properties: H/sub C/<0.5 Oe, H/sub K/<6 Oe, a resistivity /spl rho/=91 /spl mu/Ohm/spl middot/cm, a magnetoresistance ratio /spl Delta//spl rho///spl rho/<0.05%, a saturation induction B/sub s/=0.65 T, and a magnetostriction constant /spl lambda//sub s/=4/spl times/10/sup -7/. The films exhibit stable amorphous structure. The above results show that sputtered NiFeZr films emerge as a good candidate for SAL in MR heads. Some characteristics of three-layered (NiFeZr/Ta/NiFe) MR elements have also been discussed in this paper.

Permanent magnet stabilization of an overlaid MR head

Higher area density in the rigid disk magnetic recording industry is being achieved with magneto-resistive (MR) heads biased with a soft adjacent layer (SAL). The abutted and the overlaid designs are the two approaches most commonly used. Reader stability is a result of a single domain structure due to boundary control stabilization (BCS) from exchange or magnetostatic coupling. The details of a particular design determine on track and off track performance. Recent reviews and products suggest that the magnetostatically coupled abutted head design is superior to published overlaid designs. This paper describes the electrical performance and physical characteristics of another overlaid design that performs on track and off track at the recording density of 650 Mb/in/sup 2/.

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.

Impact of microstructure on stability of permanent magnet biased magnetoresistive heads

This work pertains to output voltage stability of soft adjacent layer biased magnetoresistive heads with abutted permanent magnetic films for domain stabilization. A micromagnetic model has been developed to study the effect of the permanent magnet film microstructure and the micromagnetic properties of the abutted junction interface on head stability. The impact on head stability is analyzed with respect to interfacial ferromagnetic coupling across the junction interface and intergranular exchange coupling in the permanent magnet films among other film properties.

Magnetic and electrical properties of NiFe-oxide mixture films

In order to improve the performance of magnetoresistive heads, higher saturation flux density Bs and higher resistivity /spl rho/ are preferable for Soft Adjacent Layer (SAL). NiFe-oxide (oxide=SiO/sub 2/, Al/sub 2/O/sub 3/, ZrO/sub 2/ and Ta/sub 2/O/sub 5/) mixture films were investigated for SAL. Among these films, the NiFe-ZrO/sub 2/ system is preferable because of its high Bs /spl rho/ and low coercivity. The stability of the NiFe-ZrO/sub 2/ system at 250/spl deg/C was also investigated, which shows that Bs and /spl rho/ change by annealing and the changes increase with ZrO/sub 2/ content. MR devices of 3.2 /spl mu/m width and 2.8 /spl mu/m height were fabricated and transfer curves were measured. The maximum output voltage of the device in which NiFe-12mol% ZrO/sub 2/ was employed was 23% larger than the calculated value for the device in which NiFe-Nb (Bs /spl rho/=60 Tesla /spl mu//spl Omega/cm) was assumed to be employed.

ＳＡＬバイアス法を用いたＮｉＦｅ／Ｃｕ多層膜ＭＲ素子の特性

Magnetoresistive (MR) elements fabricated and investigated for NiFe/Cu multilayers with transverse biasing structures. The magnetoresistive ratio of those elements is about 3.3%, which is 2.5 times as large as that of MR elements of a NiFe single film. The soft-adjacent-layer (SAL) biasing method is available for NiFe/Cu multilayers. The MR ratio decreases with increasing sense current owing to a rise in the temperature of the elements. The MR ratio is maintained in annealing up to 220°C, but rapidly decreases as a result of annealing at 250°C.

Micromagnetic modeling of a single element MR head

Micromagnetic modeling was used to study the behavior of a shielded, single element, exchange biased magnetoresistive head with dimensions appropriate for 10 Gb/in/sup 2/ recording. Its read sensitivity appears to be superior to that of a comparable, conventional soft adjacent layer biased head and its noise characteristics are favorable.

Numerical analysis of the magnetization in soft adjacent layer biased magnetoresistive sensors

A modified Dufort–Frankel method with relaxation is developed and applied to the static magnetization analysis of a magnetoresistive sensor, which is composed of a magnetoresistive layer magnetically fixed by a domain controlled antiferromagnetic layer, a nonmagnetic conducting layer, and a soft magnetic adjacent layer. This method is thought to be suitable for three-dimensional large-scale magnetic-multilayered systems. It clarifies the biased magnetization state of the magnetoresistive layer and soft adjacent layer with intermagnetostatic interaction.