2015年 第76回応用物理学会秋季学術講演会

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10 スピントロニクス・マグネティクス » 10.2 スピントルク・スピン流・回路・測定技術

[14p-2J-5~18] 10.2 スピントルク・スピン流・回路・測定技術

2015年9月14日(月) 15:00 〜 18:45 2J (223)

座長:森山 貴広(京大)

17:15 〜 17:30

[14p-2J-13] Reduction of bias current density using Heusler alloy spin injection layer in mag-flip spin-torque oscillator devices for microwave-assisted magnetic recording

〇(P)Subrojati Bosu1, Hossein Sepehri-Amin1, Yuya Sakuraba1, Masamitsu Hayashi1, Kazuhiro Hono1 (1.National Institute for Materials Science)

キーワード:MAMR,Heusler alloy,STO

The main challenges of microwave assisted magnetic recording (MAMR) for next generation high areal density magnetic recording are development of a mag-flip spin torque oscillator (STO) [1] consisting of the in-plane magnetized field generating layer (FGL) and the perpendicular magnetized spin-injection layer (SIL) that is able to generate a large Hac from FGL with a frequency over 20 GHz at small bias current density JC < 1.0 X 1012 A/m2 [2]. We have investigated the oscillation behavior of a mag-flip STO device (Fig. 1(a)) with 100 nm diameter circular pillar using highly spin polarized ferromagnetic Heusler alloy, Co2Fe(Ga0.5Ge0.5) (CFGG), perpendicularly magnetized with FePt as SIL to reduce JC, and also compared with a typical ferromagnetic alloy CoFe SIL. ΔR-Hex curves in Fig. 1 (b) and (c) for CFGG and CoFe SILs, respectively, for various negative dc bias currents Idc with Hex applied perpendicular to film plane (θ ~0°) reveals higher MR values for CFGG SIL than CoFe SIL. Moreover, for CFGG SIL when |Idc| > 5.5 mA a sudden jump to the intermediate resistance state at high Hex region in the ΔR-Hex curves indicates excitation of magnetization dynamics by the reflected spin current from the SIL interface. On the other hand, for CoFe SIL intermediate resistance state appears for |Idc| > 13 mA. Such difference in MR and Idc seems to be due to the higher spin polarization in CFGG than CoFe. Figures 1(d), and (e) show, ΔR-Hex for |Idc| > 9 mA, and corresponding rf signals for CFGG SIL respectively, with Hex slightly tilted θ ~7° from the film normal. A maximum f ~12 GHz has been observed for Hex ~ 10 kOe, which systematically decreases following Kittle’s equation. Moreover, the blue shift of f with Idc (not shown here) also confirms detection of oscillation perpendicular to plane for the bias current density JC ~ 0.95 to 1.15 × 1012 A/m2, which is close to the desired JC for application.