Spin-valve Heads Research Articles

Thermal and magnetic stability of unidirectional anisotropy in spin-valve magnetoresistive heads

The temperature and time dependencies of magnetic anisotropies for NiFe layers pinned by two typical antiferromagnetic films, NiO and FeMn, were studied to understand the stability of unidirectional anisotropy. Torque curves were measured isothermally after application of a magnetic field from a direction perpendicular to the unidirectional anisotropy for certain time periods. Applying the field caused the torque curve to shift toward the field direction and its amplitude to decrease. The amount of shift and the normalized decrease in the torque amplitude were proportional to the logarithmic time of the applied perpendicular field. The changes observed in the NiO/NiFe film are twice as large as those in the NiFe/FeMn film at the same holding time and temperature. The external magnetic field caused rotation in the direction of the unidirectional anisotropy and a reduction in the exchange coupling strength. These changes may be explained by the thermal fluctuation aftereffect model. The unidirectional anisotropy in the NiO/NiFe film was less stable compared with that in the NiFe/FeMn film.

ESD induced pinned layer reversal in spin-valve GMR heads

Magnetization direction of the pinned layer in the Spin-Valve giant magnetoresistive (SV) heads has been found to be reversed easily by electrostatic discharge (ESD). Thermal stress and magnetic field from ESD cause this phenomenon. This phenomenon happens only when the bias field direction by ESD current Is opposite to the magnetization of the pinned layer. The energy of magnetization reversal of the pinned layer from ESD is found to be a quarter of the ESD breakdown energy. For SV heads which consist of an AF film with higher blocking temperature, the energy becomes higher.

Scanning magnetoresistance microscopy of La0.67Sr0.33MnO3 films

We have developed a magnetic imaging scheme using the magnetoresistive spin valve head in a dc bias mode as a sensing element. By scanning the head in contact with the sample we obtain a submicron spatial resolution map of the normal component of the magnetic field in the temperature range 4.2–300 K. The writing element of the sensor can be used to alter the local magnetic structure in a controlled way. This technique was applied to image the magnetic domain structure down to 77 K in patterned thin films of La0.67Sr0.33MnO3, known for their colossal magnetoresistance. A reorientation of single or multiple domains in the films was accomplished by applying a local magnetic field with the writing element, while the effect on magnetotransport was monitored with the simultaneous measurement of current–voltage characteristics.

Pinned-Layer Magnetization Stability of Spin-Valve Heads with NiO/CoO-Bilayer, FeMn, and NiMn Antiferromagnets

An abnormal reproduced waveform was observed in spin-valve (SV) heads. We show that this abnormal wave-form was caused by instability of the pinned-layer magnetization even below the blocking temperature (Tb). In SV heads with an NiO/CoO-bilayer (NiO/CoO-SV heads), the pinned-layer magnetization is easily aligned to the track width direction and becomes unstable even at room temperature. FeMn-SV heads showed a relatively stable wave-form, in contrast to NiO/CoO-SV heads. However, below a temperature of 100°C, the pinned-layer magnetization reverses and is pinned easily to the direction of the applied current field. On the other hand, the pinned-layer magnetization in NiMn-SV heads is highly stable, mainly because of the high Tb.

Spin-Valves Using CrMnPt Antiferromagnetic Films

Spin-valve heads with Ta (5nm)/Cr45Mn45Pt10 (30nm)/Co (3nm)/Cu (2.5nm)/Co (1nm)/Ni80Fe20 (5nm)/Ta (5nm) film were fabricated and their read performance was tested. The MR ratio of the spin-valve films and the exchange-coupling field were 6.7% and 320 Oe, respectively. The output relative to the track width was 1 mV/μm with a sensing current of 4.3 mA. With the same sensing current, the readback waveform of the fabricated heads was noise-free and well biased. The temperature dependence of the output was examined for both CrMnPt and NiO spin-valve heads. The output of CrMnPt spin-valve heads at 100°C was 6% smaller than the output at room temperature. For NiO spin-valve heads, the output at 100°C was 14% lower than at room temperature. The small temperature dependence of the output for CrMnPt spin-valve heads is attributed to the large exchange-coupling field, small temperature dependence of the exchange-coupling field, and high blocking temperature.

スパッタリング雰囲気の清浄性の超高密度磁気記録デバイス用薄膜の磁気特性への影響

The ultra clean sputtering process (UC-process) was introduced in the fabrication of thin film media and spin valve type Ni-Fe/25 at% Ni-Mn/Ni-Fe tri-layered films. As a result, the UC process enables the control of the fine structure of the thin films and resulted in excellent magnetic properties. This study demonstrates that the UC-process is superior to the normal process presently used and plays an important role for the thin film media and spin valve head fabrication.

Recording performance of the combination of magnetoresistive head and thin metal evaporated tape

Thin metal evaporated (ME) tape with low remanence-thickness product (Mrδ), high coercivity (Hc) and low noise was designed to match a magnetoresistive (MR) head. This article focuses on the high density recording performance of a shielded MR head/thin ME tape media designed for use with an MR head. The PW50 measurement was adopted to certify that the depth of recording was restricted by magnetic layer thickness. Reduced second harmonic distortion at low density shows saturation-free operation of the MR head. Frequency domain measurements indicate drastically reduced ac erase noise level and higher output level at short wave length. High readback density (neglecting intertrack interference) of 1.07 Gbits/in2 with signal-to-noise ratio (SNR) after equalization of 18.7 dB was attained for a FeNi (AMR) head and 1.29 Gbits/in.2 with SNR of 20.0 dB for a spin-valve (GMR) head. The performance of the MR head/thin ME tape system was compared to commercial ME tape and thin metal particulate tape in terms of noise characteristics, depth of recording, and SNR after equalization.

Micromagnetics of spin valve tape heads

A micromagnetic model was applied to study the response of large aspect ratio spin valve heads to tape fields. The contribution of a ferrimagnetic TbCo exchange layer is analyzed. The shielded head response to tape fields is then determined by first calculating the average device permeability from a micromagnetic analysis. This permeability is included in a transmission line model to estimate flux decay. The transfer curve for the shielded device (read half-gap g=0.1 μm, head-tape spacing d=0.075 μm) is calculated for an isolated arctangent transition in low remanence Barium Ferrite (BF) tape media. Linear response occurs for |〈cos(θPINN−θFREE)〉|⩽0.4. For a dibit pulse written on the BF tape with a transition length of 0.09 μm, bit length of 2.56 and 0.256 μm, an average PW50 of 0.42 and 0.29 μm is calculated. Pulse asymmetry is −6.6% and −7.1%, respectively. The rolloff for square wave recording indicates a D50 of 96 kfci, with no significant head saturation at low linear densities. For a 1 mA sense current, a zero to peak voltage output of 80 μV/μm trackwidth is predicted. A similar analysis is done for a sinusoidal signal recorded on thick metal particle tape media. Partial head saturation is observed at intermediate linear densities, leading to a second harmonic distortion of −19.9 dB at 30 kfci.

Improvement of thermal stability and magnetoresistance recovery of Tb25Co75 biased spin-valve heads

The thermal stability of TbCo exchange biased spin valve sensors has been extended to 230 °C, by using a Co pinned layer rather than NiFe. Magnetoresistance (MR) remains essentially stable up to annealing temperatures TA of 230 °C and degrades to 1% at TA=240 °C. Providing TA does not exceed 230 °C, any loss in the MR signal can be fully recovered by applying a field perpendicular to the film plane. This improved thermal stability allows processing at higher temperatures. The unidirectional exchange in the TbCo/Co interface becomes uniaxial for TA>100 °C. Even though the unidirectional character was not recovered by any field/anneal treatment, uniaxial anisotropy above 120 Oe is maintained for TA=260 °C. Devices were fabricated using a process with a maximum temperature of 180 °C. No MR loss is found during process in test structures at wafer level. A prototype 10-μm-track width spin valve tape head for QIC applications gave a maximum output of 2.3 mVpp at 20 kfci.

NiFe/CoFeB spin-valve heads for over 5 Gbit/in/sup 2/ density recording

This paper outlines the successful use of NiFe/(Co/sub 90/Fe/sub 10/)/sub 100-x/Bx (x=5, 10%) for soft magnetic, thermally stabilized spin-valves. The GMR effect in the NiFe/CoFeB spinvalve increases after annealing. The annealing effect of CoFeB on CoFeB/Cu interfaces is investigated by high resolution TEM-EDX analysis. Merged inductive NiFe/CoFeB spin-valve heads with a read gap length of 0.18 /spl mu/m and a write gap length of 0.28 /spl mu/m having NiO(400 /spl Aring/)/NiFe(10 /spl Aring/)/CoFeB/sub 5/(10 /spl Aring/)/Cu(32 /spl Aring/)/CoFeB/sub 5/(20 /spl Aring/)/Ta(100 /spl Aring/) spin-valve film and high Bs laminated FeZrN/NiFe top poles were fabricated. Their read/write performance were tested on a low noise CoCr/sub 19/Pt/sub 5/Ta/sub 2/Nb/sub 2/ thin-film disk with an Mrt of 0.6 memu/cm/sup 2/ and a coercivity of 2600 Oe. A normalized output per track-width of 1000 /spl mu/Vpp//spl mu/m and a 50% rolloff linear density (D/sub 50/) of 182 kFCI is obtained. This performance well exceeds the performance of 5 Gbit/in/sup 2/ spin-valve heads. The measured S/N was 26.8 dB for a spin-valve head with with a narrow read track-width of 0.68 /spl mu/m, and the feasibility of 8 G bit/in/sup 2/ recording density is studied using a 1/7 code Narrow Band PRML channel.

Numerical Analysis of Spin-Valve Heads with Overlapping Leads

The read performance of spin-valve heads with overlapping leads is studied by using a micromagnetic model. In the case of hard biased spin-valve heads without an overlapped region, the sensitivity (output per lead distance) falls significantly with decreasing lead distance because of the existence of dead zones at both ends of the track. However, heads with 0.5-μm-wide overlapped regions at the ends of the sensing film have high sensitivity even if the lead distance is reduced to 0.5μm. Their output for an effective track width of 1.0μm is 30% larger than that of heads without the overlapped region when the heat generation is the same. Their output has a smaller dependence on the longitudinal bias strength, indicating a larger margin for the longitudinal bias. Spin-valve heads with overlapping leads are promising for high-track-density recording.

A high temperature stable spin valve sensor head for high density applications

In this paper, we will report a read-only spin valve that has a trackwidth of 1.4 /spl mu/m, a read gap of 0.23 /spl mu/m, and with a stripe height of 0.75 /spl mu/m. It had a corrosion resistant exchange pinning layer, Co/sub 90/Fe/sub 10//FeMnRh, that provided an exchange bias of 225 Oe. It produces a very stable signal and a normalized amplitude of 1 mv//spl mu/m/(memu/cm/sup 2/). Furthermore its asymmetry is lower that 6%. The /spl Delta/R/R of the spin valve film was 5.2% with the following structure: Ta(5 nm)/NiFe(2 nm)/Co/sub 90/Fe/sub 10/(5 nm)/Cu(2.8 nm)/Co/sub 90/Fe/sub 10/(1.2 nm)/NiFe(2 nm)/FeMnRh(10 nm)/Ta(5 nm). The spin valve heads were soaked for 96 hours in a corrosion test chamber that was operated at a temperature of 85 C and a humidity of 85%. The sensor element, the exchange bias film, the hard magnetic longitudinal bias, and the conducting leads were free from corrosion after the corrosion test. Furthermore the spin valve read-only heads were electro-migration tested in an oven operated at 120/spl deg/C, and the heads survived with the operating current up to 9 ma.

Linear Signal Analysis of Narrow Track NiFe/Cu/Co/Cu Spin-Valve Head

Linear Signal Analysis of Narrow Track NiFe/Cu/Co/Cu Spin-Valve Head

Micromagnetic Simulation of Hard Bias Field Effects on Submicron Spin Valve Heads

The three-dimensional micromagnetic simulations of submicron spin valve (SV) heads are presented. At such sensor widths, the amplitude of SV head output is reduced. An effective way to improve this reduction is to weaken the longitudinal bias field from permanent magnets. Results of simulations reveal that the magnetizations of the pinned layer near the air bearing surface rotate irregularly below a critical permanent magnet strength at a positive external medium field. This irregular rotation causes hysteresis of transfer curve. The critical permanent magnet strength decreases linearly with an increase in the reciprocal of the square of the sensor width. At the optimum permanent magnet strength, the amplitude of the sensor with 0.3 μm wide is almost the same as that of the sensor with 1.0 μm wide. It is important to evaluate the domain stability of the pinned layer when designing a SV head with submicron sensor widths.

Spin-Valve Films with PdPtMn Antiferromagnetic Layer

Antiferromagnetic film has been used as a pinning layer for a spin-valve head. For practical applications, however, a less corrosive antiferromagnetic layer than those currently available is required. We succeeded in obtaining a new PdPtMn antiferromagnetic layer with high corrosion resistance, which gave a high Hua to a coupled Ni-Fe film when annealed of a temperature lower than 230°C We fabricated spin-valve films using this Pd31Pt17Mn52 material, and obtained an MR ratio of 7.2% by annealing at 230°C although the Hc of the pinned Ni-Fe layer became larger than that when an Fe-Mn antiferromagnetic material was used. The new material is suitable for use as the pinning layer of a spin-valve film. However, further research is needed to decrease the Hc.

Recording performance of a giant magnetoresistive head on a perpendicular multilayer medium

The magnetic recording characteristics of a giant magnetoresistive spin-valve head in combination with a perpendicular disk medium have been measured. The disk medium contains a 30-nm-thick Pt/CoCrTa multilayer displaying low noise and high remanence. A pulse width of 172 nm, a signal to noise ratio of 31 dB, and a rolloff D50 point of 120 kFCI were achieved. The parametric data and window margin testing show this recording system can support recording storage density of 3.5 Gbits/in/sup 2/ using a simple peak detect channel at a data rate of 65 Mbits/s.

Micromagnetics of dual spin-valve GMR heads

Micromagnetic simulations were performed to study the biasing characteristics and playback performance of actual dual spin-valve GMR heads. Both symmetric and asymmetric dual spin valve heads were analyzed. The study shows that the symmetric dual spin-valve head is not properly biased in its patterned form, without any additional transverse biasing schemes. On the other hand, the asymmetric dual spin valve head is self-biased since in this form, the free layer is free from the demagnetizing fields arising from the pinned layers. However, opposite GMR effects with similar magnitudes would be required for the two spin valve structures in the same multilayer film.

Error rate performance of high density recording using narrow track spin-valve GMR head

To achieve the targeted areal density of 10 Gb/in/sup 2/, a highly sensitive read head with symmetric and sharp sensitivity distribution is a key requirement. In this study the off-track error rate performance was investigated using a newly developed narrow track spin-valve GMR head. The microtrack profile showed the sharp and symmetric sensitivity distribution with an effective read track width of 1.2 /spl mu/m. The minimum error rate of 3.0e/sup -8/ was achieved at 200 kBPI with 8/9 PR4-ML signal processing. The slope of the error rate at the track edge was found to be steeper than that of conventional MR head. The results indicated that the symmetric and sharp sensitivity distribution contributed to keep the off-track capability large at high track density. The intrinsically sharp and symmetric sensitivity distribution of the spin-valve head plays a great role for coming generations of 10 Gb/in/sup 2/ recording density.

5 Gb/in/sup 2/ recording demonstration with NiFe/Co/sub 90/Fe/sub 10/ spin-valve heads and low-noise thin-film disks

A high areal density of 5 Gb/in/sup 2/ (7.75 Mbit/mm/sup 2/) has been demonstrated with narrow track NiFe/Co/sub 90/Fe/sub 10/ spin-valve read heads on low-noise CoCrTaPt/CrMo-alloy thin-film disks. The MFM measurements clearly showed the write track width to be 1.2 /spl mu/m on the CoCr/sub 17/Pt/sub 5/Ta/sub 4/ thin-film media. This corresponds to 19.5 kTPI (768 track/mm) including a guard band of 0.1 /spl mu/m. The error rate performance was tested using a PR4ML channel with write precompensation. At a data rate of 33 MB/s, a practical error rate of 9.0/spl times/10/sup -6/ was obtained without error correction at a linear density as high as 257 kBPI (10.1 kbit/mm). At a linear density of 217 kBPI (8.5 kbit/mm), we obtained an error rate of less than 10/sup -8/ without error correction. With a 192-bit Reed-Solomon error correcting code, we can expected an error rate of 1.0/spl times/10/sup -14/.

Pulse distortion in MR and GMR playback heads

Distortion of the playback pulse shape due to saturation is studied via a 3-D micromagnetic model for both MR/SAL and spin-valve heads. The deviation from linearity is examined as a function of both the Mr/spl delta/ of the recording medium and the off-track position of the device. Playback voltages for isolated transitions of both polarities are calculated and their shapes are compared to linear references. The differences in structure between MR and GMR sensors result in very dissimilar distortions of the playback pulse shape under large applied fields.