Thermal stability and reliability of spin-valve films with synthetic antiferromagnet exchange-biased by IrMn

ANTlFERROMAGNETANGE-BIASED BY IrMn H. N. Fukc, K. Saito, M. Yoshikawa, K. Koui, H. Iwasaki and M. Sahashi Materials and Devices Research Laboratories, Research and Development Center, Toshiba Corporation, 72, Horikawa-cho, Saiwai-ku, Kawasaki 210, Japan Jntroduction An antiferromagnetic layer that plays an most impnrlant role in spin-valve has been investigated in order to obtain high thermal stability and reliability for use or spin-valve GMR heads in giga bits density magnetic recording lJ,z). We reported that Ir,Mn, exchange-coupled to CoFe shows a T, of 270% and is suitable for a narrow gap head structure that is nccdcd in order to realize more high density recording as IrMn shaws high H,, at lhinnrr layer thicknrss than ordered antiferromagnetic films as NiMn and PtMn". However, other papers have reporled poor IrMn properties with a T. ofbelow 250'C ",". In this study. we report the relation ktwccn lrMn crystal gram and good lrMn propertics and thc thermal stability of spin-valves with a synthetic antiferromagnet ( S y w exchange-biased by the IrMn layer. -E.&.I ' Im We believe that large KnFV is important to obtain high T. (Here, Ks is the crystal anisotropy 01 the antiferromagnetic film, and V i s the volume of the crystal grain. Namely. it is needed to make the grain size of lrMn layer grow in order lo obtain high Tw On the other hand, it was reported for CrAl antiferomagntic layer that H, is in proportion to l l D by using Malozemolf random field approximation on the assumplion that L=D ?.(Here, L is the coupling arei, and D is the grain size.) As the critical thickness for CrAl is thick, it is necessary to assume d-nD (n: cocilicienl) for lrMn with thin critical thickness. If these models are suitable, it is thought that T. increases when the grain size of IrMn layer grows lager, while H,,,dccrcascs. Figure 1 shows the grain six of lrMn layer dcpcndencc for H , , and T,. The grain size was calculatcd by using Schcrrur'a cquation from IrMn (111) XRD peak. The grain sizes were ahout equal to the lrMn layer thickness. I t was found lhal T, increases as the grain size of lrMn layer increases, while H, .decreases, and an H,, of 4WOe at R.T. and a T, o1300'C for CoFc(2nm)llrMn (10nm) spin-valves were obtained. Thermal stahilitv and reliahilitv of SvAFIlrMn spin-wilvcs The spin-valve (S.V.) film wilh a SyAF exchange-biased by the IrMn layer with high T, and high H, TalNiFelCoFelCulCoFe~ulC~~Fellr?,Mn,,(l0nm)~a, was prupared on alumina coalcd Si substrates hy DC sputtering. The IOW oxygen contcnl lrMn largcl was uscd. The lilms were annealed at 270'C for 1 -10 hours under a magnetic licld olmore Ihan 7kOe. Figure 2 shows the thermal stability fnr a reversed magnetic ticld n l 10kOe IO the pinncd layer direction. At uach temperature, it was annealed f<>r 10 minutes under the rcvcrscd m;ignclic licld. The H,.,' was defined as shown in fig.3. The pinned direction was stable ti l l about I X W C . And Ihc pinncd direction gradually changed to Ihc reversed direction a1 tcmpcralurcs i r m 201K 10 ahout 311o'C. I t is thought tu be more stahlc h r reversed magnetic liclds til l 24OT than IrMn-S.V. and PtMnS.V. with normal pinned layer. The spin-valve film wilh a SyAF exchange-biased h) Ihc lrMn layer is expccled to he strong lor ESD. Figure 4 shows thc lhcmal stahilily Ihr ii pcrpcndicular miignclic field of 2000e to pinned direclion. The time dependence of the pin dircclim 0 11 was mcasurcd ;it 200°C. SyAFllrMn spin-valve shrrws a small changc in e p u l l c s s than 4' aftcr ahnut 1110 hours even at a high temperature of200t . TEL: +81-(144-54Y-3572 FAX: t X 1 -(144-54O-l 142 Hiromi Niu Fuke Materials and Devices Rescarch hhoratnrics, Rescarch and Development Center. Toshiba Corpralinn 72, Horikawa-cho, Saiwai-ku, Kawasaki 210, Japan E-mail: hiromi.iukc~toshiba.uo.jp