Spin caloritronics: Moosa Hatami spin-dependent thermoelectrics and beyond Gerrit E.W. Bauer Reimei Institute for Materials Research & WPI-AIMR, Tohoku University Kavli Institute of NanoScience, TU Delft Spin caloritronics Thermodynamic analysis of interfacial transport and of the thermomagnetoelectric system M. Johnson and R. H. Silsbee, Phys. Rev. B 35, 4959 (1987) name alternative name electronics spintronics calorimetry caloritronics spin caloritronics subject control of charge transport spin electronics control of spin & charge transport measuring heat heattronics, thermotronics control of heat transport spin caloric transport control of spin, charge & heat transport Spin Caloritronics 4 Spin caloritronics: G.E.W. Bauer, E. Saitoh & B.J. van Wees, In: Nature Materials Insights “Spintronics”, Nature Materials 11, 391 (2012). Contents • Why? • Heat • Spin • Spin and Heat Physics of spin caloritronics • Spin-dependent (magneto) thermoelectrics o Spin-dependent Seebeck and Peltier effects o Magneto-Seebeck tunneling • Spin Seebeck/Peltier effects • Thermal spin injection • Thermal spin transfer torques • Heat-driven magnetization dynamics • Magnonic heat & spin transport • Nanoscale magnetic heat engines • Spin, planar and anomalous Nernst, Ettingshausen, and Righi-LeDuc effects • Spin-dependent heat conductance (spin heat valve) • General spin-dependent irreversible thermodynamics Not: magnetocalorics (adiabatic demagnetization) 1 STT MRAM Applied thermoelectrics Peltier spot cooling of integrated circuits © nextreme.com STT-M + IBM/Micron, Sony, Intel, Qualcomm, … Energy waste in Gcal/year underground train stations Thermoelectric conversion of waste heat Toshiba Review 63, 7 (2008) mheat scavenging/harvesting unrecycled waste heat transformer steel furnace-related waste incinerators © cosmosmagazine.com 温度(°C) Contents Metals • Why? • Heat • Spin • Spin and Heat Thomas Johann Seebeck (1770-1831) Jc V T 0 V1 Jc V2 G T1 JQ T2 J Ke Q T J Wiedemann-Franz Law: Lorenz number: c 0 Ke L0T G 2 2 kB L0 3 e lim T 0 2 Thermoelectric power T1 Peltier effect V S T J c 0 T2 T JQ Jc J Q J c T 0 T2=T Seebeck coefficient Peltier coefficient V Thermoelectric heat pump: Thermocouple: T1 SA T2 J Q A J Q J Q A B J c Jc V S B S A T B SB Heat transport in metals Heat and charge transport (electron like) E E Je> Jh Je kBT(x) EF kBT(x) EF x x Jh Jh g(E)f(E,x) f(E,x) lim S T 0 eL0T g ( ) 0 g ( F ) F Heat and charge transport (hole like) Lars Onsager Memorial at NTNU Trondheim E Je< Jh kBT (x) EF x The Nobel Prize in Chemistry 1968: “for the discovery of the reciprocal relations bearing his name, which are fundamental for the thermodynamics of irreversible processes” Jh g(E)f(E,x) lim S T 0 eL0T g ( ) 0 g ( F ) F Lars Onsager 3 Figure of merit Thermoelectrics V J c L11 L21 J T L L Q 12 22 T L12 L21 V R J Q T V T+T V+V S 1 , R1 , K 1 W Onsager reciprocity R = 1/G K S = ST electrical resistance thermal conductance Seebeck coefficient Peltier coefficient Onsager-Thomson (Kelvin) relation TH 1 ZT 1 1 ZT TL TH S 1 S 2 T R1 R2 K 1 K 2 2 ZT S 2 , R2 , K 2 S Jc K T W T JQ TH TL C.B. Vining, An inconvenient truth about thermoelectrics, NatMat (2009). Electron spin Contents up • Why? • Heat • Spin • Spin and Heat © U. Regensburg down Spin-accumulation and spin-current Stoner metallic ferromagnet F EF N Nsd D sf py 2 pF pF px Nsd D sf spin-flip diffusion length diffusion constant spin-flip relaxation time 4 Spin valve and giant magnetoresistance (GMR) Current-induced spin-transfer torque N F GMR R AP RP R AP m 2 R R 2 P R R z y ISN ISF 0 T I SN g VN VN / 2 g ↑ Onsager reciprocals (Brataas et al., 2011) LLG equation Magnetization motion causes spin currents (spin pumping, Tserkovnyak, 2002). Heff spin transfer torque L M mm J s L sm L ms Heff L ss Vs L sm Μ L T ms Μ g e Vs s N Berger (1996) Slonczewski (1996) spin accumulation • Why? • Heat • Spin • Spin and Heat spin mixing conductance Thermal spin-injection by metals FM Js M spin conductance spin pumping ↓ Contents Spin torque and spin pumping Spin currents cause magnetization motion (spin transfer torque, Slonczewski, 1996). spin-mixing conductance Thermal spin-injection by metals Jc Js G J Q 1 P ST P 1 P ST ST P ST L0T 2 spin-dependent Peltier effect V V / 2 V V T / T P E PG E G EF spin-dependent Seebeck effect JQ Mark Johnson and R. H. Silsbee (1987) 5 Single particle spin caloritronics (expt.) Experiment Spin-dependent Seebeck effect Magneto-Seebeck tunneling and magneto heat conductance Tunneling anisotropic magnetothermopower in GaMnAs/GaAs Reference Slachter et al. Walter et al., Liebing et al., Lin et al. Zhang et al. Naydenova et al. Thermal spin injection into Silicon Le Breton et al. Spin-dependent Seebeck effect ≠ spin Seebeck effect! Year 2010 2011 2012 2013 2011 T 2011 Spin-dependent Peltier effect Flipse et al. 2012 Spin heat accumulation Dejene et al. 2013 Slachter et al. (2010) Spin-dependent Peltier effect Collective effects in insulators magnetic (electric) insulator NM Onsager reciprocity holds between spin-dependent Seebeck and Peltier effects. Flipse et al. (2012) (Longitudinal) spin Seebeck effect Spin Hall effects V [V] ≠ spin-dependent Seebeck effect! spin Hall effect inverse spin Hall effect Uchida et al. (2010/2011) 6 Noise-induced spin currents (Longitudinal) spin Seebeck effect ≠ spin-dependent Seebeck effect! V [V] FM N © Kajiwara et al. Foros et al. (2005) Xiao et al. (2009) Uchida et al. (2010/2011) Onsager analysis of sSe (magn. insulators) Origin of spin Seebeck effect TF TN LsQ Xiao et al. (2010) m m0 Heff Js Js pump Js J-N noise A ' g T FM T Ne Xiao et al. (2010) Adachi et al. (2010) Collective spin caloritronics (expt.) Experiment Reference Year Spin Seebeck effect Uchida et al. Jaworski et al. 2008,2010 2010 Magnon-drag thermopower Costache et al. 2011 Thermal spin torque in spin valves Magnon heat conveyor belt Yu et al. 2010 Saitoh c.s. 2013. Parkin c.s. Unpublished. Heat current-induced domain wall motion Vs L mm M J s L sm J Q L mT Qm 0 V ISHE AJ s Re g T M sVcoh thermal field L ms L ss LQs mT0 magnon Peltier effect spin Seebeck effect m0LmQ Heff m0LsQ Vs LQQ T / T heat conductance spin Peltier effect Potential applications of spin caloritronics • Heat management and enhanced logics by magnetic tunnel junction • Spin Seebeck planar thermoelectric generator • Spin Seebeck position sensitive heat detector • Highly efficient thermal magnetization reversal • Spin caloritronic nanomachines 7 Magnetic tunnel junctions Thermopower of magnetic tunnel junctions MgO (optical): Walter et al. (2011) MgO (electrical): Liebing et al. (2011) Al2O3 (optical): Lin et al. (2011) MgO(electrical): Zhang et al. (2012) Fe () | MgO | Fe (/) 1 nm MgO CoFeB TMR - large thermopower (> 1 mV/K) - switchable thermopower (TMS > 200 %) - low heat conductance, large ZT? - thermal switching? R AP RP RP 1000% Walter et al. (2011) John Slonczewski (2010) John Slonczewski (2010) I V Torque generation efficiency: J. Xiao et al. (2010) I torque/ eV current/e F Heat assisted magnetic recording (HAMR) magnetic coherence volume spin pumping V spin torque I z S S T F T N spin torque torque/ eV ~ I /e 1 terabit per-square-inch breakthrough © Seagate/2012 8 Planar spin Seebeck generator Thermopile JQ V const . J Q L L~1m 1V m YIG t ~10-50 nm V Kirihara et al. (2012) Uchida et al. (2012) Position sensitive heat detector Spin Seebeck generators Image reconstruction Uchida et al. (2011) Primitive magnetic heat engine ferromagnets Magnetic nanoscale heat engines T1 T2 T1 Brownian motor: © www.imagesco.com T2 Continuum version of Feynman’s ratchet & pawl Heat pump: Motor: Kovalev et al. (2010,2011) Bauer et al. (2010) 9 Conclusions • Spin, charge, and heat transport are coupled in magnetic nanostructures -> spin caloritronics. • In magnetic metals the spin-dependence of the conductance causes spin-dependent thermoelectric effects. • The collective dynamics in magnetic insulators cause completely new phenomena such as the spin Seebeck effect. • Spin caloritronics provides new strategies for waste heat scavenging and heat management in nanostructures. Collaborators Sendai Oleg Tretiakov Adam Cahaya Takahiro Chiba Saburo Takahashi Isaac Acosta Europe Alireza Quaiumzadeh Arne Brataas Hans Skarsvåg Paul Kelly Delft Yanting Chen Peng Yan Fateme Joibari Yunshan Cao Hujun Jiao Akashdeep Kamra Yaroslav Blanter US Yaroslav Tserkovnyak Sendai Hiroyasu Nakayama Eiji Saitoh Koki Takanashi Kenichi Uchida Subrojati Bosu Asia Ke Xia Jiang Xiao Yan Zhou Hedyeh Keshtgar Sadamichi Maekawa Munich Sebastian Gönnenwein Mathias Althammer Michael Weiler Groningen Bart van Wees Fasil Kidane Nynke Vlietstra 10
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