4/30/2014. Electronics. Outline. Charge, Spin, and Heat Transport in the Proximity of Metal/Ferromagnet Interface. Ssu-Yen Huang

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Outline Charge, Spin, and eat Transport in the Proiit of Metal/Ferroagnet Interface Ssu-Yen uang National Taiwan

Effect (SSE) Entangled with anoalous Nernst effect (ANE) Intrinsic spin-dependent theral transport Entangled with

of Inforation Technolog G-kW-h 1. igh efficienc deices 2.

Borkar, Intel 4 In the beginning, there was onl electronics.

1 Outline Charge, Spin, and eat Transport in the Proiit of Metal/Ferroagnet Interface Ssu-Yen uang National Taiwan Uniersit Johns opkins Uniersit Introduction 1G and 2G Spintronic deices Spin current Spin all effect Spin Seebeck Effect (SSE) Entangled with anoalous Nernst effect (ANE) Intrinsic spin-dependent theral transport Entangled with agnetic proiit effect (MPE) Intrinsic Spin Seebeck effect New MR b MPE (or Spin all MR) Suar 1 2 Power Consuption of Inforation Technolog G-kW-h 1. igh efficienc deices 2. Reduction of heat dissipation Refreshing in off state 5% 20% of total electrical power Monuental proble METI / Green IT Prootion Council (2008) E. Pop, Nano Res 3, 147 (2010) 3 IC Power densit approaches that of nuclear reactor Can spin proide a solution? S. Borkar, Intel 4 In the beginning, there was onl electronics.. Electronics Charge Three iportant discoeries in Spintronics Giant Magnetoresistance (GMR) (1988*) Tunnel Magnetoresistance (TMR) (1995) Spin Transfer Torque (STT) (1996, 2000) Areal Densit Spintronics bits/in 2 *2007 Nobel Grünberg/Fert GMR increase in densit Spin 10-8 reduction in cost Spin-ale read-head 5 6 1

GMR 1 etal 2 Spin-dependent scattering Spintronic GMR and TMR Deices TMR 1 insulator 2 Spin-selectie tunneling free fied P Low R 0 1 Storage Reference AP igh R Field Sensing & Non-olatile Storage

densit Eliinate field writing word / sense lines Field (1G) Deices 7 Uniersal eor: speed as SRAM, densit as DRAM, rewritabilit as flash 8 e - Spin transfer torque electrical current affects agnetic

field Large M: spin polarier Sall M: M can be rotated Sloncewski, JMMM 159, L1 (1996) Berger, PR B 54, 9353 (1996), JAP 57, 1266 (1984), JAP 49, 2156 (1978) Waintal et al.

2 GMR 1 etal 2 Spin-dependent scattering Spintronic GMR and TMR Deices TMR 1 insulator 2 Spin-selectie tunneling free fied P Low R 0 1 Storage Reference AP igh R Field Sensing & Non-olatile Storage Non-olatile Storage: Magnetic Rando Access Meor (MRAM) Magnetic Tunnel Junction (MTJ) high R low R 1 0 Read Write Adantages: Non-olatile eor Short access tie Low power consuption Ke Challenges: igh densit Eliinate field writing word / sense lines Field (1G) Deices 7 Uniersal eor: speed as SRAM, densit as DRAM, rewritabilit as flash 8 e - Spin transfer torque electrical current affects agnetic configurations M torque sin Incident electron transitted Field Sensing & Non-olatile Storage 1G and 2G Spintronic Deices P Low R 0 1 Storage Reference AP igh R I > I C I reflected without a agnetic field Large M: spin polarier Sall M: M can be rotated Sloncewski, JMMM 159, L1 (1996) Berger, PR B 54, 9353 (1996), JAP 57, 1266 (1984), JAP 49, 2156 (1978) Waintal et al., PRB 62, (2000) 9 (1G) Field Deices Requires er large j c > 10 6 A/c 2!! What are new Spintronic Effects for 3G deices? (2G) Current (STT )Deices 10 arious all effects Charge, Spin, Theral Transport in thin fils Ordinar all effect (E.. all, 1879) Anoalous all effect (E.. all, 1880) B ( or M ) Integer quantu all effect (on Kliting, Nobel 1985) jt e jt e Fractional quantu all effect (Storer, Tsui, Laughlin, Nobel 1998) Spin all effect Inerse spin all effect E B Magnon all effect Topological all effect abe ore 11 Edwin all (1879, 1880) A student of enr JU : all Effect Walther Nernst T : Nernst Effect 12 2

all effect Anoalous all effect Spin all effect The echanis of SE 1879 1880 2004

Spin-Orbit Coupling Onl Charge Charge + Spin Onl Spin Detect b oltage Detect b

,) AE can be either sign Definite Ais but Not Definite Sign SE can be either sign

Inerse Spin all effects ISE in detects pure spin current Direct Spin all Inerse

accuulation Charge Current Spin Dependent Scattering Transerse Spin Ibalance

) Spin Current Transerse Charge Ibalance (easured b side oltage) 15 Optical

Science 306, 1910 (2004) 16 Spin Calortronics Electronics Spin Seebeck Effect

3 all effect Anoalous all effect Spin all effect The echanis of SE Spin-Orbit Coupling Electron frae sees B field with gradient B Lorent Force Spin-Orbit Coupling Onl Charge Charge + Spin Onl Spin Detect b oltage Detect b oltage Wh? Detect b what? F=q (E+ B) Definite Sign q( B) (Nagaosa et al.,) AE can be either sign Definite Ais but Not Definite Sign SE can be either sign 13 + nucleus E - electron 14 Direct Spin all s. Inerse Spin all effects ISE in detects pure spin current Direct Spin all Inerse Spin all (Optical) Obseration of Spin all effect Charge current pure spin accuulation Charge Current Spin Dependent Scattering Transerse Spin Ibalance (easured b what?) Spin Current Transerse Charge Ibalance (easured b side oltage) 15 Optical obseration SE in seiconductors ow to detect? 15 Kato et. al. Science 306, 1910 (2004) 16 Spin Calortronics Electronics Spin Seebeck Effect Charge ST spin S spin T j j ( S S )( T ) K. Uchida et al., Nature, 455, 778, (2008). Spin Spin Caloritronics eat J c =0 up J c =0 J s 0 down Spin Seebeck effect 17 T Metals, insulator, or seiconductors T Ferroagnetic etals ow to detect J S? 18 3

Detection of Spin Current b Inerse Spin all Effect Long

conerts a spin current into an electrootie force E SE Mster

dissipation? Cold side ot side E E SE D ISE J S 4?

Proportional to T Mster 1: Conduction-electron spin current

, Nature, 455, 778, (2008). 19 K. Uchida et al.

seiconductors GaMnAs/GaAs Transission of spin currents?

Metal, Insulator SSE in Insulator Reision 2 : agnon-phonon

, Nature Materials, 9, 898 (2010) E ( t) G T Where is

intentional in-plane T Transerse configuration ( T) insulator

strip and in-plane teperature gradient T indicated Intrinsic

strip detects j S Intrinsic spin Seebeck effect?

4 Detection of Spin Current b Inerse Spin all Effect Long transission of Spin Current ISE in (spin orbit scattering) conerts a spin current into an electrootie force E SE Mster 2: spin current ( s >> spin diffusion length) without dissipation? Cold side ot side E E SE D ISE J S 4? etals 6 4 Sign change 8 insulators Asetric in Sign change Proportional to T Mster 1: Conduction-electron spin current Asetric in Spin-wae spin current K. Uchida et al., Nature, 455, 778, (2008). 19 K. Uchida et al., Nature 455, 778 (2008); Nature Mater. 9,894 (2010); Kajiwara et al., Nature 464, 262 (2010) Spin Seebeck effect in broken seiconductors GaMnAs/GaAs Transission of spin currents? Transerse ( T) and Longitudinal ( T) Spin Seebeck SSE in Metal, Insulator SSE in Insulator Reision 2 : agnon-phonon drag through substrate C. M. Jaworski et al., Nature Materials, 9, 898 (2010) E ( t) G T Where is intrinsic SSE? th T ( t) sd tanh( ) Adachi et al., APL 97, (2010) Jaworski et al., PRL 106, (2011) 21 p S t t 2 sd T etal Metal intentional in-plane T Transerse configuration ( T) insulator intentional ertical T Longitudinal configuration ( T) 22 strip and in-plane teperature gradient T indicated Intrinsic Caloritronic effect (not substrate doinated)? strip detects j S Intrinsic spin Seebeck effect? Intrinsic spin-dependent theral transport? Uchida et al., Nature 455, 778 (2008) In-plane T T in-plane Uchida et al., Nat. Mater 9, 894 (2010) Jaworski et al., Nat. Mater 9, 898 (2010) uang, Wang, Lee, Kwo, and Chien, Intrinsic spin-dependent theral transport, PRL 107, (2011)

Create in-plane gradient T Consistent, Robust, but Strange th(,) Results

1 2 3 4 5 P 25 But this is phsicall ipossible! e.g.

27 This is anoalous Nernst effect with perpendicular T!

! Unifor eating fro substrate T Thin fil on substrate: in-plane and

5 Create in-plane gradient T Consistent, Robust, but Strange th(,) Results Asetric in P/Si sin θ =2000 Oe igher T Lower T ot Cold eat flow θ P 25 But this is phsicall ipossible! e.g., opposite signals at = 90 and = 270. P P T T 26 Reersed T, Sae!! Out-of-plane T!! T T =2000 Oe =2000 Oe Sign change No sign change T T ust be out-of-plane! 27 This is anoalous Nernst effect with perpendicular T!! T (Top iew) Transerse geoetr, 28 Onl T!! Unifor eating fro substrate T Thin fil on substrate: in-plane and out-of-plane gradient Anoalous Nernst effect: sensitie detector of and T E ANE T T due to substrate T substrate Sae ANE sign and alue eerwhere intentional in-plane T In the transerse configuration ( T) : where does T coe fro?

What causes out-of-plane gradient T? Electric Current s.

510-6 10-6 Theral conductiit 125 56 30 80 (W/-K) Theral conduction through substrate oerwhels!

(due to T) and SSE (due to T) Anoalous Nernst Effect (ANE) Spin Seebeck Effect (SSE) sensitie detector of and T T T 10 4 thicker!

entangled 33 S. Y. uang et. al, Phs. Re. Lett.

Nernst Effect (Transerse) 34 Intrinsic spin transport properties with in-plane T Longitudinal oltage: theral th = th + ( th - th

6 What causes out-of-plane gradient T? Electric Current s. eat Current Electrical Current eclusiel in-plane Electrical - eat Current NOT eclusiel in-plane Theral T - Resistiit (Ωc) > 1 > Theral conductiit (W/-K) Theral conduction through substrate oerwhels! + Substrate (10 4 thicker) Electricall Insulating T + Substrate (10 4 thicker) Not therall Insulating Entangleent of ANE (due to T) and SSE (due to T) Anoalous Nernst Effect (ANE) Spin Seebeck Effect (SSE) sensitie detector of and T T T 10 4 thicker!! E ANE T Both along (E SSE ) ANE and ( SSE ) additie, both are asetric in (or ) In transerse configuration: SSE and ANE are entangled 33 S. Y. uang et. al, Phs. Re. Lett. 107, (2011) Reoal of out-of-plane gradient ( T) Theral (Longitudinal) Substrate-Free saple ( T onl) T substrate Planar Nernst Effect (Transerse) 34 Intrinsic spin transport properties with in-plane T Longitudinal oltage: theral th = th + ( th - th )cos 2 M Setric in b using a substrate free saple Transerse oltage: Planar Nernst effect sin2 M cos 2 M sin2 M Necessar Signatures of fil with in-plane T! 35 Spin Seebec effects with in-plane T and out-of-plane T SSE in Metal T etal Metal intentional in-plane T Transerse configuration SSE + ANE Substrate-free SSE in liit Insulator No strong eidence of SSE insulator intentional ertical T PRB 83, (2011), PRL 109, Longitudinal (2012), PRL 111, configuration (2013), PRB 88, (2013), PRB SSE (2013), PRB 88, (2013), and etc. 36 6

7 R AE () R AE () th (a.u.) th () R 4/30/2014 Metals (Cu, P, ) on Insulators (Si, YIG) /YIG s. /Si all Ferroagnetic Insulator: YIG (Y 3 Fe 5 O 12 ) ll M/Ms /YIG! cos 2 Ferroagnetic! : Magnetic Proiit effects Line T M/M S T -1.0 YIG (Oe) shape anisotrop uang et al., Phs. Re. Lett., 109, (2012) 37 Cu/YIG Non-agnetic /Si Non-agnetic Cu (10n)/YIG II (10n)/Si (Oe) 38 Thickness dependence of in P/YIG & /YIG s. New MR P(t)/YIG (t)/yig YIG QuickTie?and a decopressor are needed to see this picture. QuickTie?and a decopressor are needed to see this picture t (n) /YIG and P has opposite t dependence 20 constant at large t 0 at sall t All oents contribute New MR 0 at large t New MR increases at sall t Magnetic Proiit effect Moents near interface contribute Anoalous all Effect in /YIG R () M Z B Z I (10n)/YIG (koe) T(K) = R O B + R S 4M K 5K (10n)/YIG K 250 K K 100 K 100K 50 K 250K K 5 K K (koe) 41 Theral oltages in /YIG and /Si (all saples) Share dependence /YIG Theral oltage New MR ( ) th II 0.2 (10n)/YIG ( 12 ) th T = 11 K 0.05 (15n)/Si ( 12 ) th ( 36 ) th 0.05 Cu (10n)/YIG (Oe) 42 R () 7

R() R() 4/30/2014 Thicknesses dependence of theral oltage /YIG P/YIG siilarl large (up to 6 µ/k) ) th 60 /YIG 40 P/YIG 20 P/Si 0 2 10 ANE onl t (n) R () P/YIG Theral 835.4 835.2 II 1 835.

8-1000 -500 0 500 1000 (Oe) 30 (E ANE ) P T th () 43 Induced agnetic oents in /Ni, /Co, & /Fe X-ra Magnetic Circular Dichrois (XMCD) /Ni 0.29 μ B /Fe 0.5 μ B PRL 85, 413 (2000) Phs.

076 B X ra Circular dichrois (XMCD) 7 laers Assuing all hae sae oent 6Å YIG All four laers are significantl polaried.

8 R() R() 4/30/2014 Thicknesses dependence of theral oltage /YIG P/YIG siilarl large (up to 6 µ/k) ) th 60 /YIG 40 P/YIG 20 P/Si ANE onl t (n) R () P/YIG Theral II P(10n)/YIG ( ) th ( 12 ) th (Oe) 30 (E ANE ) P T th () 43 Induced agnetic oents in /Ni, /Co, & /Fe X-ra Magnetic Circular Dichrois (XMCD) /Ni 0.29 μ B /Fe 0.5 μ B PRL 85, 413 (2000) Phs. Status Solidi A 196, 33 (2003) Magnetic proiit effect in /YIG /Co 0.68 μ B PRB 60, (1999) 44 Induced agnetic oents in /YIG (1.5n)/YIG 300K B 20K B X ra Circular dichrois (XMCD) 7 laers Assuing all hae sae oent 6Å YIG All four laers are significantl polaried. Au laers are essentiall unpolaried Spin densit Four laers Au or Coparison of /YIG and Au/YIG /YIG s. Au/YIG Intrinsic SSE Spin Seebeck 50 larger Obsered New MR Yes No Anoalous all Yes No Moent (Theor) Yes No Moent (XMCD) Yes Not obsered Phs. Re. Lett. 110, (2013) spin current detector: Au? 45 Phs. Re. Lett. 110, (2013) New Magnetoresistance New Magnetoresistance in /YIG: Magnetic Proiit Effect in the plane M (I) M/Ms Anisotropic MR s. New MR I() & M P New MR P(10n)/Si ,, (degree) 360 () > T () sae scan (2.5n)/YIG ,, (degree) () > T () sae scan M (I) Ɵ M (I) () T () scan = scan scan = constant () () New MR!! scan = scan scan = constant 47 PYSICAL REIEW B 87, (R) (2013) 48 8

9 Sheet resistance () Sheet resistance () R() R() Sheet resistance () Sheet resistance () 4/30/2014 Spin all Magnetoresistance (SMR) /P s. Au/P Spin all MR in /YIG: charge/spin current conersion (Nakaaa et al.,) SOC etals/no agnetic oent SE ISE j e j e The reflection J s depends on STT ρ () > ρ T () ; ρ () = ρ () Nakaaa et al. Phs. Re. Lett. 110, (2013) (2.5n)/YIG ,, (degree) SMR: SOC etals on YIG No agnetic oent Spin current ais (independent of ) 49 MR =MR +MR 38.0 (3n)/P(5n)/(1.5n) Au(3n)/P(5n)/Au(1.5n) ,, (degree),, (degree) New MR Magnetic Proiit can be detected in etal fro XMCD and NEW MR 50 (10-3 ) 38.0 Au(3n)/P(5n)/Au(1.5n) t P (n) P(t P ) Thicknesses dependence (own Moents) + New MR (induced Moents) New MR s. Spin all MR ,, (degree),, (degree) 12 Au(3 n)/p(t P )/Au(1.5 n) 15 (3 n)/p(t P )/(1.5 n) = 40 koe 8 4 (10-3 ) 38.0 (3n)/P(5n)/(1.5n) 37.8 New MR 12 = 40 koe t P (n) /P(t P )/ (10-4 ) ,, (degree) (t )/YIG (2.5n)/YIG = 15 koe New MR t (n) (t )/YIG 51 Eperiental obseration Induced Moent? (AE, XMCD) /YIG New MR Yes Yes /P + New MR Yes? /YIG BB New MR Yes? Au/P No? Au/YIG No new MR No? Spin all MR Prediction? New MR obsered in cases with induced oents Magnetic proiit effect accounts for all cases 52 Suar Transerse Spin Seebeck ( T) (etals, seiconductors, insulators): Entangleent with anoalous Nernst ( T) Intrinsic spin-dependent theral transport on substrate free saple Longitudinal Spin Seebeck Effect (ferroagnetic insulators): Coplicated Magnetic proiit effects in Entangleent of SSE and ANE New MR in etals and Insulator new MR in /YIG, P/YIG, /YIG BB, and /P No new MR in Au/YIG and Au/P New MR b agnetic proiit effect or Spin all MR? is not an ideal spin current detector (agnetic proiit effects): Au is better spin current detector 53 Acknowledgeent Johns opkins Uniersit: Prof. Chia-Ling Chien, Danru Qu, Bingfeng Miao Uniersit of Ariona: Prof. Weigang Wang National Tsing ua Uniersit: Prof. J. Ranien Kwo Acadeia Sinica: Dr. Shang-Fan Lee Uniersit of Delaware: Prof. John Q. Xiao Ariona State Uniersit: Prof. Tingong Chen Uniersit of California, irine: Prof. Ruaiqn Wu Chinese Acade of Science: Prof. Jianwang Cai US NSF Taiwan NSC 54 9

Longitudinal Spin Seebeck Effect in Silver Strip on CoFe Film. and K. Y. Wang, 1,b) Semiconductors, Chinese Academy of Sciences, Beijing , China

Longitudinal Spin Seebeck Effect in Silver Strip on CoFe Film. and K. Y. Wang, 1,b) Semiconductors, Chinese Academy of Sciences, Beijing , China Longitudinal pin eebeck Effect in ilver trip on CoFe Fil Y. heng, 1,2 M. Y. Yang, 1 Y. Cao, 3 K. M. Cai, 1 G. N. Wei, 1 G. H. Yu, 3 B. Zhang, 1 X. Q. Ma, 2,a) and K. Y. Wang, 1,b) 1 tate Ke Laborator of