講演情報
[11a-E208-11]Investigation of Critical Thickness of AgSn-spacer in Polycrystalline Co2(Mn,Fe)Ge Heusler based CPP-GMR for Read Head Applications
〇Bang Do1, Kazuumi Inubushi1, Tomoya Nakatani2, Hirofumi Suto2, Taisuke Sasaki2, Yuya Sakuraba2, Tomoyuki Sasaki1 (1.Advanced Products Development Center, Technology & Intellectual Property HQ, TDK Corp., 2.Research Center for Magnetic and Spintronic Materials (CMSM), National Institute for Materials Science (NIMS))
キーワード：
CPP-GMR、read head、polycrystalline Heusler alloy
Current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) reader based on Heusler alloys is promising candidates for next-generation hard disk drive read heads. As the areal density magnetic media increases, magnetic bit sizes continue to shrink. Consequently, the read gap which is determined by the total thickness of the sensor stack must be reduced to accommodate these smaller conditions. In this study, the effect of AgSn-spacer thickness of 2.5 to 5.0 nm on magnetoresistance ratio in polycrystalline Co2(Mn, Fe)Ge Heusler-based CPP-GMR devices fabricated on ceramic substrates was investigated, with the aim of determining the critical thickness of AgSn-spacer.
For a meaningful comparison of MR ratios, the statistically intrinsic MR ratio was estimated from the slope of the linear fit of the ΔR versus minimum resistance which are proportional to pillar sizes. The estimated intrinsic MR values are 15.8% and 8.9% for a pseudo-SV and a practical IrMn bottom-pinned SV with a 5-nm-thick AgSn-spacer, respectively. The lower MR in the bottom-pinned SV is attributed to greater lattice mismatch originating from the bottom pin IrMn layer, as indicated by its higher surface roughness 3.0 nm compared to 0.9 nm in the pseudo-SV. The MR is slightly reduced from 15.8 to 14.2% with moderate scatter as the AgSn-spacer thickness is reduced from 5.0 to 3.5 nm. Subsequently, it sharply decreases to below 10% with a large scatter at 3.0 nm. This reduction is attributed to the loss of exchange coupling, which prevents the pillar from fully achieving the antiparallel configuration as the AgSn-spacer becomes excessively thin. To further enhance the MR ratio and minimize the critical thickness of the AgSn-spacer, it is necessary to reduce the surface roughness of underlying pinning layers. These findings provide a basic for optimizing the critical thickness of the AgSn-spacer in future CPP-GMR read heads
For a meaningful comparison of MR ratios, the statistically intrinsic MR ratio was estimated from the slope of the linear fit of the ΔR versus minimum resistance which are proportional to pillar sizes. The estimated intrinsic MR values are 15.8% and 8.9% for a pseudo-SV and a practical IrMn bottom-pinned SV with a 5-nm-thick AgSn-spacer, respectively. The lower MR in the bottom-pinned SV is attributed to greater lattice mismatch originating from the bottom pin IrMn layer, as indicated by its higher surface roughness 3.0 nm compared to 0.9 nm in the pseudo-SV. The MR is slightly reduced from 15.8 to 14.2% with moderate scatter as the AgSn-spacer thickness is reduced from 5.0 to 3.5 nm. Subsequently, it sharply decreases to below 10% with a large scatter at 3.0 nm. This reduction is attributed to the loss of exchange coupling, which prevents the pillar from fully achieving the antiparallel configuration as the AgSn-spacer becomes excessively thin. To further enhance the MR ratio and minimize the critical thickness of the AgSn-spacer, it is necessary to reduce the surface roughness of underlying pinning layers. These findings provide a basic for optimizing the critical thickness of the AgSn-spacer in future CPP-GMR read heads