Spin-valve heads with synthetic antiferromagnet CoFe/Ru/CoFe/IrMnY. Huai, J. Zhang, G. W. Anderson, P. Rana, S. Funada, C.-Y. Hung, M. Zhao, and S. Tran Citation: Journal of Applied Physics 85, 5528 (1999); doi: 10.1063/1.369883 View online: http://dx.doi.org/10.1063/1.369883 View Table of Contents: http://scitation.aip.org/content/aip/journal/jap/85/8?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Exchange bias of spin valve structure with a top-pinned Co 40 Fe 40 B 20 ∕ Ir Mn Appl. Phys. Lett. 93, 012501 (2008); 10.1063/1.2956680 Role of oxygen exposure in different positions in the synthetic spin valves J. Appl. Phys. 93, 7708 (2003); 10.1063/1.1555773 Use of a permanent magnet in the synthetic antiferromagnet of a spin-valve J. Appl. Phys. 91, 2176 (2002); 10.1063/1.1433937 Spin-valve thermal stability: The effect of different antiferromagnets J. Appl. Phys. 87, 5726 (2000); 10.1063/1.372502 Spin-valve giant magnetoresistive films with antiferromagnetic Ir-Mn layers J. Appl. Phys. 81, 4004 (1997); 10.1063/1.364920

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Spin-valve heads with synthetic antiferromagnet CoFe/Ru/CoFe/IrMnY. Huai,a) J. Zhang, G. W. Anderson, P. Rana, S. Funada, C.-Y. Hung, M. Zhao,and S. TranSpin-valve Materials/Process/Testing, Read-Rite Corporation, 44100 Osgood Road, Fremont,California 94539

Spin-valve~SV! films Si~100!/Ta30/NiFe50/CoFe20/Cu26/CoFe23/Ru7/CoFe20/IrMn50/Ta30~inÅ! exhibit a room temperature~RT! giant magnetoresitance~GMR! ratio of 8.5% with an effectiveexchange pinning field (Heex) of ;1.3 kOe and an antiferromagnetic~AF! saturation field~Hs! of;6.0 kOe. The synthetic spin valve shows a GMR ratio of 5.0% at 150 °C withHeex.500 Oe, whilea conventional spin valve@Si~100!/Ta50/NiFe50/CoFe20/Cu28/CoFe22/IrMn50/Ta50 in Å# has aGMR ratio of 5.0% withHex,200 Oe. The synthetic sample also showed a superior thermalstability with a RT GMR value of 6.9%~compared to 6.1% for conventional sample! after an annealat 250 °C for 10 h. Shielded narrow track synthetic SV readers demonstrated high amplitude, largedynamic range, and excellent magnetic stability, indicating extendibility for ultrahigh density readhead applications. ©1999 American Institute of Physics.@S0021-8979~99!71308-3#

I. INTRODUCTION

Spin valves are being used as the next generation of readheads for high-density magnetic recording. Spin-valve sen-sors using a laminated antiparallel pinned layer~syntheticantiferromagnet! have demonstrated improved thermal andmagnetic performance compared to conventional spin valvesusing same AF pinning materials.1,2 One of the advantages ofsynthetic spin-valves sensors is the large dynamic range dueto improved magnetic bias of the free layer. This results fromthe effect of the controllable demagnetization field from syn-thetic antiferromagnet on the free layer. Another advantageis the large effective exchange pinning field, which results inmagnetic stability of the sensors. In this paper, we presentthermal and magnetic properties of the spin-valve films andheads biased using the CoFe/Ru/CoFe/IrMn synthetic anti-ferromagnet.

II. EXPERIMENT

Spin-valve films were deposited in an Ar pressure of3.0–5.0 mT on 4 in.@100# Si wafers. The depositions weredone in a cluster sputtering tool consisted of a four-target dcplanetary magnetron module and static modules with a typi-cal base pressure of;131028 Torr. In the planetary mod-ule, the substrates are attached to a spinner assembly withaligning magnets, which is mounted onto a circular turntable.The individual layer thicknesses are controlled with a reso-lution of ,1 Å by computer regulation of the turntable rota-tion speed, sputtering power, and pressure. Sputtering ratecalibrations were performed by both atomic force micros-copy and x-ray reflectivity measurements of single films.

The GMR and magnetization measurements were carriedout using a four-point quasi-static tester~QST! and avibrating-sample magnetometer~VSM!. Heads were testedon a QST for transfer curves and a Guzik 1701 precision spinstand for recording performance.

III. RESULTS AND DISCUSSION

Typical GMR versus applied magnetic field and magne-tization versus applied fieldM -H loops of a spin-valve filmTa30/NiFe50/CoFe20/Cu26/CoFe23/Ru7/CoFe20/IrMn50/Ta30~in Å! are shown in Fig. 1. A saturation field~Hs—thefield required to bring two strongly antiferromagneticallycoupled CoFe/Ru/CoFe layers into a parallel orientation! of6.0 kOe was observed from theM -H loop. Figure 1~b! is alarge-field GMR curve where all magnetization were alignedparallel at theHs. The magnetization configuration of the

a!Electronic mail: yiming.huai@readrite.com

FIG. 1. Representative GMR vs applied magnetic field~b! and M -H loop~a! of a spin-valve sensor having a structure of Ta30/NiFe50/CoFe20/Cu26/CoFe23/Ru7/CoFe20/IrMn50/Ta30~in Å!. The insert in~a! shows M -Hloop for the annealed sample~at 250 °C for 10 h in a field of 10 kOe!.

JOURNAL OF APPLIED PHYSICS VOLUME 85, NUMBER 8 15 APRIL 1999

55280021-8979/99/85(8)/5528/3/$15.00 © 1999 American Institute of Physics

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two ferromagnetic CoFe layers~PF1 is the layer adjacent toAFM layer, PF2 is the one adjacent to the spacer Cu layer!and the free layer are schematically illustrated. The GMRcontribution from CoFe/Ru/CoFe~,1%! was included in thedata. The insert shows the low-field GMR curve, resultingfrom spin-valve effect (DR/R57.8%). An effective ex-change field (Heex) of 1.3 kOe~defined as the field at whichthe GMR amplitude is half of the maximum from the small-field GMR curve! was obtained, compared toHex5450 Oefrom a conventional spin-valve film of Ta50/NiFe50/CoFe20/Cu28/CoFe22/IrMn50/Ta50~in Å!. The largeHeex

is attributed to the very thin effective pinned layer thickness,which is the difference of two strongly antiferromagneticallycoupled CoFe layersDtPF (Heex}1/DtPF). It should be em-phasized that one of the advantages of synthetic spin-valvesis the largeHeex, which results in high magnetic stability ofthe synthetic sensors.

The Ru thickness in the synthetic antiferromagnet CoFe/Ru/CoFe/IrMn is a very sensitive parameter. In a previousstudy of Co/Ru multilayers, the first AF coupling peakwas found at tRu58 Å.3 In this investigation,

@CoFe20 Å/Ru9 Å#10 showed a perfect AF coupling betweenthe CoFe layers attRu59 Å, with zero remnant magnetiza-tion andHs;10 kOe. Figure 2 shows the GMR andHs ver-sus tRu for Ta40/NiFe50/CoFe20/Cu26/CoFe22/Ru(t)/CoFe25/IrMn50/Ta40~in Å!. It is noted that the saturationfield ~Hs! for samples withtRu53,4 Å exceeds our VSMfield limit ~13 kOe!. These data were plotted here atHs513 kOe. The AF coupling region ranged from 3–10 Å,with peaks attRu;3 Å andtRu59 Å. It should be noted thatAF coupling is not perfect aroundtRu;3 Å ~significant rem-nant magnetization is present!, while AF coupling is almostperfect aroundtRu59 Å. Ferromagnetic coupling was ob-served attRu;12 Å with a Hex;200 Oe~compared toHex

5450 Oe with a pinned layer CoFe22 Å in a conventionalIrMn SV!. The GMR ratio is almost constant in the AF cou-pling region (tRu53 – 10 Å). A larger GMR value at ferro-magnetic coupling (tRu512 Å) is attributed to the lower re-sistance state at higher fieldH, where all magnetizations~PF1, PF2, and free layer! are aligned in parallel.

Figure 3 shows GMR andHeex variation as a function ofpinned layer thickness,tPF1 and tPF2 with a fixed differencetPF12tPF253 Å. The GMR value was observed to be maxi-mum at tPF1;30 Å. Heex varies in approximately a 1/tPF1

fashion. This can be understood sinceHeex reflects the satu-ration field~Hs! of AF interlayer exchange coupling betweenPF1 and PF2, which is inversely related to CoFe layer thick-

FIG. 2. GMR andHs versustRu for Ta40/NiFe50/CoFe20/Cu26/CoFe22/Ru~t!/CoFe25/IrMn50/Ta40~in Å!.

FIG. 3. GMR andHeex vs pinned layer PF1 thickness (tPF1-CoFe) for Ta30/NiFe50/CoFe10/Cu26/CoFe~PF2!/Ru7/CoFe~PF2-3!/IrMn50/Ta30 ~in Å!.The difference of PF12PF253 Å was fixed.

FIG. 4. GMR curves at the elevated temperature of 150 °C for~a! thesynthetic SV Ta30/NiFe50/CoFe20/Cu26/CoFe23/Ru7/CoFe20/IrMn50/Ta30 ~in Å!, and ~b! a conventional SV Ta50/NiFe50/CoFe20/Cu28/CoFe22/IrMn50/Ta50~in Å!.

5529J. Appl. Phys., Vol. 85, No. 8, 15 April 1999 Huai et al.

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ness byHs;JAF /MstFA ~whereMs andJAF are the satura-tion magnetization and the strength of AF interlayer ex-change coupling!.

Comparison of the thermal stability between IrMn syn-thetic and conventional spin-valve films was performed byinsitu MR measurement at elevated temperatures~up to150 °C! and by annealing samples in a vacuum of 131026 Torr at 250 °C for 10 h in a magnetic field of 10 kG.Both synthetic ~Ta30/NiFe50/CoFe20/Cu26/CoFe23/Ru7/CoFe20/IrMn50/Ta30 in Å! and conventional samples~Ta50/NiFe50/CoFe20/Cu28/CoFe22/IrMn50/Ta50 in Å! ex-hibit the same RT GMR ratio of 7.8% and similar lineartemperature dependence of MR with a value of;5% at150 °C. Figure 4 shows GMR data obtained at 150 °C forboth samples. As can be seen, the synthetic sample showed acleaner GMR curve, havingHeex.500 Oe. The conventionalIrMn sample showed a very hysteretic GMR curve withHex;170 Oe, which is not desired for high-density recordinghead application. The synthetic sample also showed betterthermal stability with a GMR value of 6.9%~compared to6.1% for conventional sample! after an anneal at 250 °C for10 h. It is impressive that the strong interlayer coupling be-

tween the CoFe layers separated by 7 Å Ru still remainedafter such a high-temperature and long-time anneal, asshown in the insert of Fig. 2~a!.

Integrated write/read heads with narrow track syntheticspin-valve reader elements were fabricated. An abutted per-manent magnet junction was used for domain stabilization ofthe free layer. Pinned layer orientation was controlled by atransverse anneal in a magnetic field. The read element widthranges from 0.7 to 1.0mm. Figure 5 shows the transfer curveof a 1.0mm reader. The transfer curve is virtually free fromBarkhausen jumps, highly linear, and symmetric for a fieldup to 200 Oe, indicating a large dynamic range and designextendibility. For readers with large stripe heights, the dy-namic range is smaller due to the weaker demagnetizationfield from the free layer.

Synthetic SV heads show good recording performanceon the spin stand. The insert in Fig. 5 shows the readbackwave form of a 0.7mm reader at 5.0 mA. The wave formwas clean, symmetric and stable. The average low frequencyTAA for 0.7 mm readers was 954 uV, or 1.36 mV/mm, whentested with a 0.55 memu/cm2 Mrt disk. The best head deliv-ers an amplitude above 2 mV/mm. Good bit error rate~BER!performance is achievable at up to 300 kfci linear densityand 17.5 MB/s data rate with a PRML channel.

IV. CONCLUSIONS

Spin-valve films with synthetic antiferromagnet CoFe/Ru/CoFe/IrMn were developed. In addition to large GMRratio, synthetic SV structures show very large effective ex-change field and excellent thermal stability. Narrow tracksynthetic SV readers demonstrated high amplitude, large dy-namic range, and excellent magnetic stability, indicating ex-tendibility for ultrahigh density read head applications.

ACKNOWLEDGMENTS

The authors thank S. Campbell, H. Singh, M. Shipman,and A. Yav for sample preparation and MR measurement.

1V. S. Speriosu, B. A. Gurney, D. R. Wilhoit, and L. B. Brown, presentedat the INTERMAG’96 Conference, Seatttle, 1996; H. Berg, W. Clemens,G. Gieres, G. Rupp, W. Schelter, and M. Vieth, IEEE Trans. Magn.32,4624 ~1996!.

2J. L. Leal and M. H. Kryder, J. Appl. Phys.83, 3720~1998!.3S. S. Parkin, N. More, and K. P. Roch, Phys. Rev. Lett.64, 2304~1990!.

FIG. 5. Transfer curve of a 1.0mm read element. The read bias current is5.0 mA. Five traces were overlapped. The inset shows readback wave formof a 0.7mm reader at 5.0 mA.

5530 J. Appl. Phys., Vol. 85, No. 8, 15 April 1999 Huai et al.

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