From Basic Magnetic Concepts To Spin Currents (Introduction) - PowerPoint PPT Presentation

European School on Magnetism, Cluj 2015 From Basic Magnetic Concepts To Spin Currents (Introduction) Laurent Vila Institut Nanosciences et Cryogénie , CEA, Grenoble, France N F I F Pure spin current Spin waves Spin-polarised current

The discovery of Giant Magnetoresistance M. N. Baibich et al., Phys. Rev. Lett. 61 , 2472 (1988), A. Fert, P. Grunberg Nobel prize 2007  Ultra High Vaccum deposition techniques, Thin films / atomic empilements + Spin dependent conduction ρ α    1 ρ  Antiferromagnetc coupling -> anti-parallel state + Fe Cr Fe

Band structure : ferromagnetism and transport Density of states Spin dependent Magnetic order conductivity Asymétrie Polarisation p F Competition between: exchange, magneto-static,    F F 2 current model : j j j magneto-cristalline, external field 

Modeling ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ρ α    1 ^ ^ ρ ^ ^ ^  ^   2 R R R R       ( ) R P ( ) R AP  sf R R 2   2 CSRM then CPP-GMR model Valet & Fert, PRB 93’

Spin injection at F/ NM interface Ferromagnetic | Non-magnetic Spin dependent current density   N N j j   F F  j j  Characteristic length   Electrochemical N F  potential sf Spin diffusion length Current polarisation From C. Chappert, A. Fert, and F. Van Dau, Nature Materials 6 , 813 (2007)

Magnetization manipulation by spin current From C. Chappert, et al, Nature Materials 6 , 813 (2007) Spin transfer torque J. Slonczewski JMMM 1996 L. Berger PRB 1996 Precessional regime Domain wall displacement Magnetization reversal (HF emission) (memories) (electrical commutation) J. Grollier, APL 78 (2001) O. Boule, Nat. Phys. (2007) M. Klaeui, PRL 95 (2005)

Charge to Spin current conversion by Spin Orbit Coupling: at Ferromagnetic | Non-magnetic interfaces  Spin Hall Effect Lead to GMR effect and spin transfert Torque Localized Spin-Orbit interaction  Rashba-Edelstein Effect By charge current injection Spin pumping Heat gradient,…

Spin Orbit effects in Ferro-Magnetic / Non-Magnetic tri-layers Ox, NM FM NM Pt/Co/Al 2 O 3 , Ta/CoFeB/MgO, Pt(t)/Co(/Ni)/P(t)…. Efficient systems to propagate DW or to switch magnetization with in plane currents (and for skyrmions) Spintec, Cornell, Tohoku, IBM, Kyoto,… very active field of research SOT + DMI Miron et al Nature 2011, Liu et al Science 2012, Emori et al Nat. Mat., Ryu et al Nat. Nano. 2013,…

Spin Orbit effects in Ferro-Magnetic / Non-Magnetic tri-layers Ox, NM FM NM Pt/Co/Al 2 O 3 , Ta/CoFeB/MgO, Pt(t)/Co(/Ni)/P(t)…. Efficient systems to propagate DW or to switch magnetization with in plane currents (and for skyrmions) Spintec, Cornell, Tohoku, IBM, Kyoto,… very active field of research SOT + DMI The nature of DW revealed by (NV center) scanning nanomagnetometry, T. Hingant, L. V. et al, Nat. Commun. 2015

Spin Orbit effects in Ferro-Magnetic / Non-Magnetic bi-layers FM NM Spin Hall effect How to efficiently transfer spins from NM to FM ? What is the source of the SOT

Spin Orbit effects in Ferro-Magnetic / Non-Magnetic bi-layers FM NM Rashba effect ? Spin momentum lock-in at Rashba interfaces and Topological Insulator Rashba-Edelstein effect

Spin Orbit effects in Ferro-Magnetic / Non-Magnetic bi-layers FM NM Spin currents in presence of Domain walls Interplay between spin current and DWs walls, Spin Orbit Torque ?

Spin current induced by FM/NM junction Spin Orbit Coupling Spin Hall and Rashba effects Johnson, Silsbee 1985, Jedema 2001 Spin waves Spin Pumping Thermal Spin Injection F NM F V Silsbee, Monod 1979, Tserkovnyak, Bauer 2002 A.Slachter et al. Nat. Phys. 2010 Kajiwara et al . Nature Phys. 2010 Saitoh 2006

Spin transport in Lateral Spin Valves Non local measurements, separating charge and spin currents       N N N N N N j j j j j j   C S Lateral spin transport in Metals, S.-C.s or carbon based hybrid structures: µ N -to access material parameters,  N µ -to find optimum spin injection/detection j   V N conditions, -to exploit spin currents…  N µ j  N X = L X = 0 Charge    N N N 0 j j j current   C Spin    N N N 0 j j j current   S

Nonlocal spin valve measurement Cu Cu 0.4 Cu P Ie 0.2 V/I (m Ω ) Cu V+ 0 V- -0.2 AP Py 2 Py 1 -0.4  -1000 -500 0 500 1000 Magnetic field (Oe) Detector in parallel P x d Charge neutral point shifts upward.

Nonlocal spin valve measurement Cu Cu 0.4 Cu P Ie 0.2 V/I (m Ω ) ∆ R S Cu V+ 0 V- -0.2 AP Py 2 Py 1 -0.4  -1000 -500 0 500 1000 Magnetic field (Oe) Detector in antiparallel AP x d Charge neutral point shifts downward.

Probes configurations and expected results F1 F2 NL 0 Δ R s 0 GMR ~2 x Δ R s (NL) 0

Non-Local results NiFe/Al T=77K, L=200nm GMR NL 46m Ω 21m Ω Δ Rs(GMR) ~ 2 x Δ Rs(NL) Sum of the spin accumulation at the two interfaces P. Laczkowski et al, APEX 4 , 063007 (2011)

NiFe/( Cu or Al ) lateral spin valves T=77K, L=150nm Py/Al Generally a few mΩ at low temperature Yang et al. Nat. Phys. 2007 : Py/Cu, 18.5 mΩ , T=10K, Py/Al, T=300K 24.2m Ω Py/Cu 21.3m Ω L sf , with P~45% T=300K T=77K Al ~450nm ~750nm Cu ~300nm ~770nm P. Laczkowski et al, APEX 4 , 063007 (2011)

NiFe/( Au, Cu or Al ) lateral spin valves T=77K, L=150nm 5.4m Ω 18.5 mΩ R Balance between & sinh -1 (L N /l N sf ) F R N R F /R N ~ 0.1 - 0.2 with Al & Cu Al, Cu ~ 0.5 for NiFe/Au sinh -1 (L N /l N sf ) Au sinh - sf ) 1 (d N /l N R F I s R N I c L N /l N sf

Enhancement of the spin accumulation by lateral confinement Coll. A. Fert, J.M. George, H. Jaffrès Opened vs Confined Geometries P. Laczkowski, Phys. Rev. B 85 , 220404 (R) (2012)

4-wires circuitry : lsf in NM, STT, SHE Out of equilibrium of spin accumulation  Spin sink experiment to measure lsf in NM Side view T. Kimura et al , PRB (2005)  Insertion of a magnetic dot for STT) Yang et al, Nature Phys 2008 1 2 3 W. F. Savero Torres V/I(m  ) 13 V/I (m Ω ) 12 11 -0,2 -0,1 0,0 0,1 0,2 B(T B (T)

Pure spin-current for spin Hall effect and magnetization swithcing Shadow evaporation Spin Hall effect for in-vacuum interface fabrication Magnetization switching Valenzuela et al, Nature 2006 Yang et al, Nature Phys 2008

Spin current induced by FM/NM junction Spin Orbit Coupling Spin Hall and Rashba effects Johnson, Silsbee 1985, Jedema 2001 Spin waves Spin Pumping Thermal Spin Injection F NM F V Silsbee, Monod 1979, Tserkovnyak, Bauer 2002 A.Slachter et al. Nat. Phys. 2010 Kajiwara et al . Nature Phys. 2010 Saitoh 2006

Inverse spin Hall effect by ferromagnetic resonance and spin pumping Absortion derivative P = 200 mW FMR NiFe(15)/Pt(5)// lorentziane 80 V voltage peak at ISHE V (  V) resonance field Saitoh APL 2006 SHE Tserkovnyak PRL 2004 40 0.08 0.10 0.12 0.14 Silsbee, PRB 1979 H (T) Magnetization precession + Interfacial Electronic coupling + spin to charge conversion in FM at FM/NM in NM

Ferromagnetic resonance (FMR) //CFB(15)/Al(5) P=200 mW dX"/dH (a.u) f= 9.6786 GHz 500 600 700 800 900 1000 Field (Oe)  H res   H pp FMR is a power technique: •Magnetic anisotropies (angular dependence, frequency dependence) •Magnetic transition (temperature dependence) •Magnetic coupling •..etc

Ferromagnetic resonance - Spin pumping Enhancement of damping constant: dX''/dH (a. u.) Spin pumping effect Tserkovnyak et al. 2002 CFB(15)  Spin mixing conductivity π   4   M t α  α s F g CFB(15)/Pt(5) / FM N M e f f µ FM g B -0.01 0.00 0.01 H-H res (T) Note: Not always  α is only due to SP

ISHE by FMR - Spin pumping Spin pumping and ISHE: E. Saitoh et al. APL 2006 dX''/dH (a. u.)  Voltage ISHE: symmetrical Lorentzian peak at H res  Note: symmetrical contribution can also be due to other effects in the FM layer (AMR or PHE, AHE, ..IAHE or ISHE?) CFB(15)/Pt(5) V ISHE V ISHE 0 V (  V) R NM R NM I C I C -100 R FM R FM Ando et Al. 2008 -200 -0.01 0.00 0.01 H-H res (T)

Spin Pumping and spin to charge current conversion •Spin-pumping – ISHE or IEE: – Pure spin currents – Easy lithography (if any) – Spin  Charge: Simple electrical detection (dc voltage measurement) Ando, Saitoh (2009) Also som e diffic ult ies ex ist … Determining the spin current  Many variables FMR Spin current ISHE or IEE H. Nakayama et al , Phys. Rev. B 85, 144408 (2012) Voltage

Spin Pumping and spin to charge current conversion •Spin-pumping – ISHE or IEE: – Pure spin currents – Easy lithography (if any) – Spin  Charge: Simple electrical detection (dc voltage measurement) Also som e diffic ult ies ex ist … Determining the spin current  Many variables From the ISHE voltage measurement : V  ISHE I C R t  θ  NM tanh( ) I W j C SHE sf S  2 sf

The Spin Hall Angle and Spin Diffusion Length in Pt •Platinum is widely studied, but results are scattered H. Nakayama et al , Phys. Rev. B 85, 144408 (2012) Values found in the literature are not consistent and spread on one order of magnitude.