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M.R. Ibarra
Institute of Nanosciencie of AragónLaboratory of Advanced MicroscopiesCondensed Matter Physics Department
Spin, charge and energy transport in novel materialsHvar, Croatia, October 1 - 7, 2017
Charge and spin currents
JS = 0
Jc
Jc = 0
JS JS
Jc = 0
Jc: charge current JS: spin current
Spin current: no Joule heating!
Conduction-electronspin current
Spin wave (magnons)spin current
Spin current detection: Inverse spin hall effect
𝑱𝑱𝑪𝑪 =𝜃𝜃𝑆𝑆𝑆𝑆𝜌𝜌𝐴𝐴
2𝑒𝑒ℏ
𝑱𝑱𝑺𝑺 × 𝝈𝝈
High SOC metal
Saitoh, E., Ueda, M., Miyajima, H., & Tatara, G. (2006). Conversion of spin current into charge current at room temperature: Inverse spin-Hall effect. Applied Physics
Letters, 88(2006), 1–4.
5
Spin Seebeck effect effect: Spin current generation by heat
)( NFB
SS TTkGI −−=
H. Adachi et al. PRB 83, 094410 (2011), Rep. Prog. Phys. 76, 036501 (2013)
J. Xiao et al. PRB 81, 214418 (2010)
7
Longitudinal spin Seebeck effect (LSSE)
Longitudinal SSE setup
paramagnet
ferromagnet
Inverse spin Hall effect:
SHE s∝ ×E j σ
K. Uchida et al.,Appl. Phys. Lett. 97, 172505 (2010).
Spin Seebeck basic principles
• Spin current proportional to applied thermal gradient
• Injected spin current converted in electric voltage by the inverse spin Hall effect
H. Adachi et al. Phys. Rev. B 83, 094410,& Rep. Prog. Phys. 76, (2013) 036501
𝐸𝐸𝐼𝐼𝑆𝑆𝑆𝑆𝐼𝐼 =𝜃𝜃𝑆𝑆𝑆𝑆𝜌𝜌𝐴𝐴
2𝑒𝑒ℏ
𝐽𝐽𝑆𝑆 × �⃗�𝜎
𝐼𝐼𝑆𝑆 = −𝐺𝐺𝑆𝑆𝑘𝑘𝐵𝐵ℏ
(𝑇𝑇𝐹𝐹 − 𝑇𝑇𝑁𝑁)
J. Xiao et al. Phys. Rev. B 81, 214418
Magnon emission associatedwith spin accumulation at themetal-ferromagnet interface (Takahasi et al ICM 2009)
Spin angular momentumtransfer at the interface:Magnon and elecronspin currentinterconversion(Steven et al. PRB 86 (2012) 214424)
SPIN CURRENT AT THE INTERFACES
10
Fe3O4
Pt
Fe3O4
SSE in [F/N]n multilayers
Pt
Combined PLD & Sputtering
KrF Laser (λ = 248 nm)
PLD-sputtering (Neocera Llc) P180-sys
(Neocera Llc)
Sputtering module
12
Atomic resolution morphological characterization
MgO/(Fe3O4/Pt)
STEM-HAADF image
0,21 nm MgO
Fe3O4
Interface Fe3O4/MgO
0,39 nm
Pt
a~ 0,83 nm
Fe3O4
Pt
Fe3O4
50 nm
MgO
Fe3O4
Pt
FIB-Pt-C
14Atomic resolution chemical mapping of the interfaces
SSE vs number of Fe3O4/Pt bilayers
-8 -6 -4 -2 0 2 4 6 8-10
-5
0
5
10
V ML /
∆T
(µV/
K)
H (kOe)
n = 1 n = 2 n = 3 n = 6
T = 300 K
n = 1
n = 6
SSE voltage enhancement with incresing number of Fe3O4/Ptbilayers
50 nmMgO
Fe3O4
Pt
50 nm
Ramos et al. Phys. Rev. B 92, 220407(Rap. Comm.) (2015)
-6 -4 -2 0 2 4 6
-0.5
0.0
0.5
1 x Pt/Fe3O4(tF), 300K
tF = 40 nm
(Vy/∆
T) (L
z/Ly)
(µV
/K)
H (kOe)
tF = 160 nm
tFPt
Fe3O4MgO
-6 -4 -2 0 2 4 6
-0.5
0.0
0.5 n = 4
H (kOe)
(Vy/∆
T)(L
z/Ly)
(µV/
K)
n = 1
n x Pt/Fe3O4(40), T=300 K
PtFe3O4
MgO
4 x
Fe3O4
Pt (15 nm)t (nm)
2mm
7mm
SSE dependence on Fe3O4 thickness
A. Anadón et al. 2016) APL (2016)
16
Dependence of SSE versus metal/insulator interlayer
Spin current across the multilayer must be considered
-8 -6 -4 -2 0 2 4 6 8-30
-20
-10
0
10
20
30
V ML /
∆T
(µV/
K)
H (kOe)
n x Fe3O4/Pt(tN) n = 1 n = 6
GSSE
T = 300 K
Pt 15 nm
Pt 7 nm
Optimized configuration
-8 -6 -4 -2 0 2 4 6 8
-30
-20
-10
0
10
20
30 n = 12n = 6
V ML/∆
T (µ
V/K)
H (kOe)
T = 300 K
n = 1
[Fe3O4(23)/Pt(7)]n
Largest SSE voltage measured in a thin film based structure!!
VML ≈ 28 µV/ K !!
20
Mechanism of LSSE enhancement in multilayer systems
Essence of LSSE enhancement: Boundary conditions for spin currents flowing normal to P/F interfaces
(i) spin currents must disappear at the top and bottom surfaces(ii) spin currents are continuous at the interfaces
Spin
cur
rent
PtFe3O4 Fe3O4
T = 300 K
z
PtFe3O4
Magnon spin current
Electron spin current
Qualitative agreement with experimental results
0 1 2 3 4 5 6 70
2
4
6
8
10
experiment
T = 300 K
S SSE (µV
/K)
Number of Fe3O4/Pt bilayers (n)
0.00
0.02
0.04
0.06
0.08
0.10
model
<JS>
Average SSE voltage measured:
𝐽𝐽𝑆𝑆 =1𝑡𝑡𝑁𝑁𝑛𝑛
�𝑖𝑖=1
𝑛𝑛�
𝑧𝑧𝑖𝑖=0
𝑡𝑡𝑁𝑁
𝑑𝑑𝑑𝑑 𝐽𝐽𝑠𝑠(𝑖𝑖)(𝑑𝑑)
Maximum spin current at central interlayers
Envelope curve(JS(z)):
Ramos et al. Phys. Rev. B 92, 220407(Rap. Comm.) (2015)
22
23
K. Uchida et al. Phys. Rev.B 95, 184437 (2017)
Spin peltier effect
24
K. Uchida et al. Phys. Rev.B 95, 184437 (2017)
25
Strong enhancement of the spin peltier effect in multiple bilayers
26
Spin Seebeck device
Wide area, low cost thermoelectric devices
Conventional charge thermoelectric device:
Many thermocouples necessaryHigh cost, difficulty in integration
T-gradient over centimeter scale neededThin film device difficult
Spin-Seebeck thermoelectric device
Many thermocouples unnecessaryLow cost, ultimate integration
T-gradient over nanometer scale is sufficientThin film device possible
(IMR, Tohoku Univ. / NEC / ASRC, JAEA/Zaragoza)
SSE thermopilesBilayer Multilayer
TP2TP1
Spin current conversión at the interfaces F/N gives rise to anstrong enhancement of the thermospin effects in multiplebilayers and constitutes an excellent play ground for thestudy of new physical phenomena and promising for devicesapplication
29K. Uchida et al. review Proceedings of the IEEE 104, 1499 (2016)
LSSE Termopower LSSE power factor
Development of thin-film thermoelectric SSE baseddevices
Strategic Japanese-Spanish Cooperative Research Program Nanotechnologies and new materials for environmental
challenges
