1. Preparation of (Fe,Mn) 3 O 4 nanoconstriction for magnetic memory application Tanaka lab Takayoshi Kushizaki M1 colloquium 11/16/2011 ( 磁気メモリ応用を目指した (Fe,Mn) 3 O 4 ナノ狭窄構造の作 製 )

2. We aim to realize large MR using (Fe,Mn) 3 O 4 For ubiquitous information technology Magnetic memory (MRAM) Highly integrated memory devices Magnetoresistance (MR) effect plays the key role in the operation. Introduction

3. Magnetoresistance effect ( 磁気抵抗効果 ) Resistance change induced by magnetic field (H) MR (%) H (Oe) High “0” Law “1” Introduction 20 10 0 Fe/Al 2 O 3 /Fe

4. Spin polarization ( スピン偏極率 ) The degree to which the spin is aligned with a given direction P=0.5P=1P=0 E EFEF E EFEF E EFEF Introduction

5. H Ferromagnet insulator Ferromagnet Julliere equation Basic structure: magnetic tunneling junction Example : Tunneling magnetoresistance (TMR) Introduction

6. (Fe,Mn) 3 O 4 : Mn-doped Fe 3 O 4 High spin polarization (P = 0.6-1.0) High Curie temperature (T c = 800K) Physical properties can be tuned via external fields H, E, h Introduction large MR at RT

7. J. Appl. Phys. 95, 5661 (2004) Fe 3 O 4 -SiO 2 Granular structure TMR structure J. Appl. Phys. 41, 387 (2002) Fe 3 O 4 AlO X CoFe Pseudo-spin-valve Ni 80 Fe 20 Cu Fe 3 O 4 Attempts towards large MR effect J. Appl. Phys. 103, 07D702 (2008) MR @RT 14% 5% 1% The spin coherence is lost at the heterointerface. （ヘテロ界面・複合界 面） Introduction

8. Preparation of a ferromagnetic nanoconstriction Ni 60 nm Phys. Rev. B 75, 220409 (2007) Realization of large MR using (Fe,Mn) 3 O 4 ( ナノ狭窄構造 ) Strategy Ni Appl. Phys. Lett. 97, 262501 (2010) 50 nm Only one material!! No heterointerface Introduction

9. Parallel Anti-parallel Mechanism of “domain wall” MR Constricted structure Introduction magnetic wall ( 磁壁 ) Wire structure without constriction

10. Estimation of “domain wall” MR Phys. Rev. Lett. 83, 2425 (1999) J. Magn. Magn. Mater. 310, 2058 (2007) d S FMO nanoconstriction SCSC MRAM With downscaling (d and S C ), the MR is greatly enhanced! Introduction P = 0.9

11. electrode( 電極 ) substrate Towards FMO nanoconstriction However, it is difficult to pattern oxide nanostructure, especially, the narrowest part (< 100 nm). In this work, we have attempted to fabricate the FMO nanowire as the first step.

12. Recipe for FMO nanoconstriction 1. FMO nanowire 2. Au/Ti electrode 3. FMO magnetic domain pad Fabricate and evaluate step by step

13. Controlling the height Nanowires Controlling the width TargetPulsed laser Pulsed Laser Deposition (PLD) Fabrication of nanowires using sidewall deposition Resist Transferring the thickness of film deposited, which can be controlled in Å-scale, to the width of nanowire pattern

14. 50 μm Top view (SEM) 100 nm 140 nm 40 nm Cross-section 100 nm 40 nm Size controllability width ： 30 - 150 nm height ： 50 - 150 nm length ： 100 μm - 14 Large area formation of FMO nanowires TED: FMO wire + Al 2 O 3 [1012] [1210] [1014] Al 2 O 3 (220) FMO (311) FMO (440) FMO ×

15. Road to FMO nanoconstriction 1. Polycrytalline FMO nanowire (sub-100 nm scale) 2. Au/Ti electrode

16. Electrode gap: 4 μm 1 μm Au/Ti electrode Capture a single nanowire for the characterization Au/Ti

17. 17 Ⓐ H FMO polycrystalline NWs were successfully fabricated with my recipe!! Capture a single nanowire for the characterization MR measurement

18. Summary  Fabrication FMO polycrystalline nanowires Width: 30-150 nm Height: 50-150 nm Length: over 100 μm The final step: FMO magnetic domain pad ongoing  Characterization Confirmed the ferromagnetic character of FMO nanowires from MR measurements

20. 100 μm Photo lithography system 64 unit/cm 2 Electrode pattern nanowires Capture a single nanowire for the characterization

21. 直観的解釈 ( スピン蓄積・ ΔR の起 源 ) V-  V+  磁化平行磁化反平行 ΔV スピン蓄積とスピン緩 和 の結果生じる界面電圧 電子注入方向 スピン蓄積 ※電荷は蓄積しない 電流一定より、 ΔV が ΔR にな る

22. FMO 狭窄構造で予想される磁気抵抗 値 J. Appl. Phys. 103, 07D702 (2008) 40 nm 2d=50 nm 1 μm 10 nm 理論 1 ：磁壁の圧 縮 理論 2 ： ” スピン蓄積誘起 ” 磁気抵 抗 

23. 10μm CF 4,O 2 plasma パターン作製 ( ナノインプリント ) レジスト 2 基板 レジスト 1 基板 : Al 2 O 3 (0001) レジスト 1: 熱硬化レジス ト (nanonex NXR-2030) レジスト 2:UV 硬化レジス ト (nanonex NXR-3032) 基板面出す ( エッチング ) 作製プロセス ① CF 4 : 10sccm 50W 2min 2.0Pa O 2 : 10sccm 50W 2min 1.0Pa モール ド UV 高い端面平坦性 大面積・一括

24. 結晶化 ( ポストアニー ル ) FMO ナノワイヤー Ar plasma レジスト除去 形状を整える ( イオンミリング ) サイドウォー ル蒸着 作製プロセス ② ターゲット : Fe 2.5 -Mn 0.5 -O P base : ～ 10 -6 Pa P O2 ： 10 -4 Pa 基板温度 : 室温 蒸着角度： 60° P base : ～ 10 -6 Pa P O2 ： 10 -4 Pa 温度： 400 ℃ 時間： 5h 浸漬 :6h 、 90 ℃ (1- メチル -2 ピロリドン ) ECR 3min FMO

25. Mo AFM tip MoO 3 Mo electrode Pulsed laser Deposition of Mo Oxidation of Mo (AFM lithography) Lift off MoO 3 Deposition of FMO Lift off Mo FMO Final step: AFM lithography

26. 狭窄構造作製可能寸法 狭窄 ( ワイヤー ) 幅 20 ～ 200 nm パッド幅 100 nm ～ 狭窄長さ 50 nm ～

27. 予想される磁気抵抗特性 外部磁場 0 Phys. Rev. B 75, 220409 (2007) 狭窄有 狭窄無 LSMO 狭窄構造 8K