Microwave Dynamics and Phase Locking in Spin Transfer Nanocontacts W. H. Rippard, M. R. Pufall S. Kaka*, S. E. Russek, T. J. Silva National Institute of Standards and Technology, Boulder, CO J. A. Katine Hitachi Global Storage Technologies San Jose, CA Supported by: NIST Nanomagnetodynamics DARPA SpinS program NIST OMP Office * Now at Seagate Research Labs, Pittsburgh, PA
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Microwave Dynamics and Phase Locking in Spin Transfer
Nanocontacts
W. H. Rippard, M. R. PufallS. Kaka*, S. E. Russek, T. J. Silva
National Institute of Standards and Technology,Boulder, CO
J. A. KatineHitachi Global Storage Technologies
San Jose, CASupported by: NIST Nanomagnetodynamics
DARPA SpinS programNIST OMP Office
* Now at Seagate Research Labs,Pittsburgh, PA
Outline
IntroductionSpin transfer effectsDevice geometry
Spin transfer induced dynamicsin plane fieldsout of plane fields
Phase locking of devices
Injection locking to source
Mutual synchronization of oscillators
Summary
0.1 0.2 0.3 0.4 0.5 0.6 0.7
-200
-100
0
100
200
V Osc
(µV)
Time (ns)
Idc= 7.85 mA
Idc= 7.8 mA
Idc= 7.6 mA
Idc= 7.4 mA
Magnetodynamics
Larmor term:precession
My
Mz
Mx
M
H
10 1 eff
dm m Hdt
µ γ= − ×r rr
Precession
H
Spin Torque
Damping
M
Spin Torque Term
Spin torque cancounteract damping
1 1 21
J( )
2inj
z s
m m mel Mε γ
+ × ×h r r v
1Larmor Damping SpinTransfer
dm T T Tdt
= + +r
M Initial
My
Mz
Mx
0 1 1( )effm m Hµ γα− × ×rr r
MFinal
H
Damping term:aligns M with HEFF
MInitial
Slonczewski 1996
TSpin Transfer ≅ TDampingJ ~ 107A/cm2
Device Schematic
V+
Au
Cu“Fixed” layer
“Free” layerInsulator
~50 nmV-
5 nm
20 nm
Measurement setup
Detection:40 GHz Spectrum
Analyzeror
Sampling scopeDC current in
Device
bias teehigh bwprobes
Spinwave radiation
Micromagnetics
Measured signal results from IDC and GMR effect
Nanocontact Dynamics Device Schematic
• Step DC current• Measure DC R, microwave
power output
5 6 7 8 924.8
25.0
25.2
25.4
Res
ista
nce
(Ω)
Current (mA)
9.6 9.7 9.8 9.9 10.0
0.0
0.1
0.2
0.3
0.4
6 mA
6.5 mA 7 mA
7.5 mA
8 mA
8.5 mA
9 mA
Pow
er (p
W)
Frequency (GHz)
Devices are nanoscale current controlled microwave oscillators
Au
Cu
~50 nmT = 300K
“Free” layer“Fixed” layer
In-Plane Applied Fields
0.0 0.2 0.4 0.6 0.8 1.00
10
20
30
40
Field (T)
26.2 ±0.5 GHz/T
Freq
uenc
y (G
Hz)
Small-angle FMR frequency7.5
6.9
7.2
7.8
5 6 7 8
-0.23 GHz/mA
Current (mA)
Freq
uenc
y (G
Hz)
Current Response Field Response
Consistent with large angle version of FMRQualitative behavior in accordance with
Slonczewski equation
φ ≈ 80˚H
M
Out of Plane Fields
Precession occurs about the applied field directionlarger tunablity with current
Low IDemag ≈ Ms
Heff=Happ-Hdemag
Demag ≈ 0 THigh I
0.5 0.6 0.7 0.8 0.9 1.0
20
25
30
35
40
Freq
uenc
y (G
Hz)
Field (T)
Tunability:20 GHz to >40 GHz
Field Response
Device Output
Integrated voltage output:
V = 850 µV
Maximum GMR response:
∆R = 250 mΩI = 10 mA
∆V = 2.5 mV
Lower bound: Impedance mismatch not accounted forBoth frequency and power indicate approaching ~80° precessional angles