preparation of (fe,mn) 3 o 4 nanoconstriction for magnetic memory application tanaka lab takayoshi...
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Preparation of (Fe,Mn)3O4 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)3O4 ナノ狭窄構造の作製 )
We aim to realize large MR using (Fe,Mn)3O4
For ubiquitous information technology
Magnetic memory (MRAM)Highly integrated memory devices
Magnetoresistance (MR) effect plays the key role in the operation.
Introduction
Magnetoresistance effect ( 磁気抵抗効果 )
Resistance change induced by magnetic field (H)
%501001000
1000500
)( 1000
0
% ρ
ρρ
H
HHMRMR (%)
H (Oe)
High “0”
Law “1”
HH under y resistivit:ρ
Introduction
20
10
0
Fe/Al2O3/Fe
Spin polarization ( スピン偏極率 )
The degree to which the spin is aligned with a given direction
P=0.5
FF
FF
EDED
EDEDP
P=1P=0E
EF
E
EF
E
EF
Introduction
H
Ferromagnetinsulator
Ferromagnet
%1001
22
2
P
PMRJulliere equation
Basic structure: magnetic tunneling junction
Example : Tunneling magnetoresistance (TMR) Introduction
(Fe,Mn)3O4: Mn-doped Fe3O4
High spin polarization (P = 0.6-1.0) High Curie temperature (Tc = 800K)Physical properties can be tuned via external fields
H, E, hn
Introduction
large MR at RT
J. Appl. Phys. 95, 5661 (2004)
Fe3O4-SiO2
Granular structureTMR structure
J. Appl. Phys. 41, 387 (2002)
Fe3O4
AlOX
CoFe
Pseudo-spin-valve
Ni80Fe20
CuFe3O4
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
Preparation of a ferromagnetic nanoconstriction
Ni
60 nm
Phys. Rev. B 75, 220409 (2007)
Realization of large MR using (Fe,Mn)3O4
( ナノ狭窄構造 )
Strategy
Ni
Appl. Phys. Lett. 97, 262501 (2010)
50 nm Only one material!!
No heterointerface
Introduction
Parallel
Anti-parallel
Mechanism of “domain wall” MR
Constricted structure
Introduction
magnetic wall ( 磁壁 )
Wire structure without constriction
600
500
400
300
200
100
0
14012010080604020
=2 =5 =10 =50
d(nm)
Mag
neto
resi
stan
ce(%
)
Estimation of “domain wall” MR Phys. Rev. Lett. 83, 2425 (1999) J. Magn. Magn. Mater. 310, 2058 (2007)
dS
CS
SFMO nanoconstriction
SC
MRAM
onconstricti ofsection -cross:Sc
onconstrictinon ofsection -cross:S
length channel :d
With downscaling (d and SC), the MR is greatly enhanced!
Introduction
P = 0.9
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.
Recipe for FMO nanoconstriction
1. FMO nanowire
2. Au/Ti electrode
3. FMO magnetic domain pad
Fabricate and evaluate
step by step
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
50 μmTop view (SEM)
100 nm
140 nm 40 nm
Cross-section
100 nm
40 nm
Size controllabilitywidth : 30 - 150 nmheight : 50 - 150 nm
length : 100 μm -14
Large area formation of FMO nanowires
TED: FMO wire + Al2O3
[1012]
[1210]
[1014] Al2O3
(220) FMO(311) FMO(440) FMO
×
Road to FMO nanoconstriction
1. Polycrytalline FMO nanowire (sub-100 nm scale)
2. Au/Ti electrode
Electrode gap: 4 μm
1 μm
Au/Ti electrode
Capture a single nanowire for the characterization
Au/Ti
Au/Ti
17
Ⓐ
H
FMO polycrystalline NWs were successfully fabricated with my recipe!!
Capture a single nanowire for the characterization
MR measurement
Summary
Fabrication FMO polycrystalline nanowires Width: 30-150 nmHeight: 50-150 nmLength: over 100 μm
The final step: FMO magnetic domain pad
ongoing
CharacterizationConfirmed the ferromagnetic character of FMO nanowiresfrom MR measurements
100 μmPhoto lithography system
64 unit/cm2
Electrode pattern
nanowires
Capture a single nanowire for the characterization
直観的解釈 ( スピン蓄積・ ΔR の起源 )
V-m
V+
m
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
FMO 狭窄構造で予想される磁気抵抗値
J. Appl. Phys. 103, 07D702 (2008)nm 80
9.0
F
P
d
FPMR F
2100
40 nm
2d=50 nm1 μm
10 nm
25cS
S
nm 160/20 KAW
nm 2233 32223
0
W
WD
理論 1 :磁壁の圧縮
理論 2 : ”スピン蓄積誘起”磁気抵抗
207%
10μm
CF4,O2plasma
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 : Al2O3(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
CF4: 10sccm 50W 2min 2.0Pa
O2: 10sccm 50W 2min 1.0Pa
モールド
UV
高い端面平坦性大面積・一括
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 :Fe2.5-Mn0.5-O
P base :~ 10-6PaPO2 : 10-4Pa基板温度 : 室温蒸着角度: 60°
P base :~ 10-6PaPO2 : 10-4Pa温度: 400℃時間: 5h
浸漬 :6h、 90℃(1-メチル -2ピロリドン )
ECR 3min
FMO
Mo
AFM tip
MoO3Mo
electrode
Pulsed laser
Deposition of Mo Oxidation of Mo(AFM lithography)
Lift off MoO3 Deposition of FMO Lift off Mo
FMO
Final step: AFM lithography
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 ~
予想される磁気抵抗特性
抵抗
外部磁場0
Phys. Rev. B 75, 220409 (2007)
狭窄有
狭窄無
LSMO 狭窄構造
8K