Spin pumping and tuning of magnetization damping by spin Hall currents. Hubert Głowiński

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1 Spin pumping and tuning of magnetization damping by spin Hall currents Hubert Głowiński Institute of Molecular Physics, Polish Academy of Sciences, Poland This work has been carried out within Project No. NANOSPIN PSPB-045/2010 supported by a grant from Switzerland through the Swiss Contribution to the enlarged European Union.

2 Outline Spin currents and spin pumping Rashba SO effect on interfaces Finemet+Al : Fe66.5Cu1Nb3Si13.5B9Al7 Ferromagnetic resonance Gilbert damping (low damping) Capping Pt layer FM/NM interface Spin Hall effect DSHE & ISHE

3 SPIN CURRENT J S in metallic systems Spin Hall angle GENERATION of SC (DSHE) DETECTION of SC (ISHE)

4 Spin pumping & detection of spin current? at interface

5 Spin pumping spin memory loss J.-C. Rojas-Sánchez et al., PRL 112, (2014)

6 Spin-memory Loss Main conclusion: spin-memory loss at interface induces a strong spin current depolarization different spin diffusion length measured in FMR and ISHE experiment J.-C. Rojas-Sánchez et al., PRL 112, (2014)

7 SP in the presence of SO coupling Conventional theory without SO: scattering theory (Tserkovniak) Conventional theory: influence of disorder at interface influence of SOC (spin-memory loss) SOC: effect Rashba Rashba! Γo SP cond. across interf. without disorder η Rashba factor ξ back-flow factor Chen, Zhang PRL 114 (2015)

8 SP in the presence of SO coupling (THEORY) ~ 7 nm -2 ~ 8 nm spin diffusion length ~ ev nm ~ 11 nm -1 ~ 9 ev ~ 5 nm mean free path of Rashba parameter of back-flow factor increase in α due to SP Chen, Zhang PRL 114 (2015)

9 SP in the presence of SO coupling spin-memory loss Or spin current jump Theory: spin-pumping formalism in the presence of SOC origin of spin-memory loss at interfaces without SO with SO Chen, ZhangPRL 114 (2015)

10 Finemet Finemet (Fe 73.5 Cu 1 Nb 3 Si 13.5 B 9 ) with its nanocrystalline microstructure provides: High permeability (~10 5 ) High saturation magnetization (~ 1.2 T) High squareness Low magnetostriction (~10-6 ) Y. Yoshizawa, S. Oguma, K. Yamauchi, J. Appl. Phys. 64 (10) (1988) 6044 Nanocrystalline soft magnetic material Finemet, Hitachi Metals, Ltd.

11 Frequency [GHz] VNA-FMR measurements of Al substituted Finemet Field [koe] ω γ 2 = H FMR ( H + 4πM ) FMR eff Linewidth [Oe] Frequency [GHz] 3 nm

12 Why Finemet+Al.?. Fe66.5Cu1Nb3Si13.5B9Al7 Permalloy widely used α = & H o = 10 Oe CoFeB low damping α = but H o = Oe FINEMET + Al * - α = & H o = 3-7 Oe! epi YIG ** - α = & H o = 2-8 Oe Essential issue for FM: damping as low as possible Ho

13 VNA-FMR with CPW Thickness (nm) 0.5 nm/mm Pt X (mm) x A Finemet thin film with wedged Pt capping layer VNA-FMR CPW 16 f=7 GHz f: 5mm 7mm 8mm 9mm 10mm 11mm 13mm f=7 GHz 5mm 7mm 8mm 9mm 10mm 11mm 13mm 3-40 GHz Ho (Oe) mm 17mm 15mm 17mm 0 19mm Magnetic field (Oe) 19mm Magnetic field (Oe) thickness dpt (nm)

14 STRUCTURE of Finemet-Al with a Pt wedge nm roughness 0.12 nm nm AFM

15 Finemet-Al with a Pt wedge for 7 GHz AFM Low roughnesswith maximum for discontinuous Pt Maximum in Η corresponds to maximum in RMS Hr modulation

16 SPIN PUMPING in Finemet-Al capped with Pt conventional theory Fe-Al-30 nm Pt wedge : 0 7 nm OK, but this region is ill defined g eff = cm -2 λ sf = 2.5 nm

17 CALCULATIONS of α within the framework of SOC Pt islands 1 3ML thick Γo ~ 7 nm -2 α R ~ ev nm k F ~ 11 nm -1 α E F ~ 9 ev η ~ ξ ~ λsd ~ 8 nm spin diff. length t Pt (nm) λm ~ 5 nm mean free path

18 After ion beam etching g eff = cm -2 l sf =3 nm α α = gµ B g eff 4πM t s Al F (1 e 2t l sf Pt ) d Pt (cm) After ion etching sample s thickness is not homogenous XRF intensity position on sample [mm]

19 MODULATION of the resonance field (field-torque?) X 3 GHz Disentangled with spectr. splitting g (t Pt) : 2 2.2! 5 nm

20 CHANGES in α and modulation of resonace field modulation resonance field Fe/Pt Theory

21 Gold buffer 0.02 Au/Ti 3.5 4πM eff (kg) Thickness (nm) α Au 5 Co 2,5 Au Ti 4 Si thickness of gold (nm) Untypical decrease of damping with thickness increase of gold

22 Surface roughness Matczak et al., J. Appl. Phys. 114, (2013); K. Kurzydłowski i M. Lewandowska "Nanomateriały inżynierskie konstrukcyjne i funkcjonalne"

23 Surface roughness Au 8 Ti 4 Si Co 0-3 K K = s + pr d K V Matczak et al., J. Appl. Phys. 114, (2013);

24 Simulation 0.2 Depolarization probability 22% do 60% g eff Cu/Pt Co/Pt δ Thickness (nm) 0.3 Co/Cu Thickness (nm) J.-C. Rojas-Sánchez et al., PRL 112, (2014)

25 Nonlocal damping mechanism 0.02 Au/Ti α thickness of gold (nm)

26 ISHE measurements Spin current through NiO barrier

27 ISHE measurements FMR signal [a.u.] 0,15 0,10 0,05 0,00-0,05-0,10-0, ,6 GHz θ = 0 o FMR signal [a.u.] 0,10 0,05 0,00-0,05-0, ,6 GHz θ = 180 o -0, ISHE [uv] 3 2 ISHE [uv] Magnetic Field [Oe] Finemet 18nm / NiO 10nm / Pt 10nm Magnetic Field [Oe]

28 Spin pumping measurements NiO 1-8.5nm t NiO = 4 nm 180 Finemet Al 7 20 nm V ISHE (µv) V ISHE (µv) Finemet/NiO/Pt H (Oe) ISHE observation H (Oe) H0 [Oe] position [mm] α Slight enhancement of damping position [mm]

29 Damping measurements NiO 1-8.5nm Finemet Al 7 20 nm α H0 [Oe] position [mm] 0 Slight enhancement of damping position [mm]

30 Litography Contacts Waveguide Finemet/Pt

31 SNA-FMR Spectrum Analyzer H 9 8 t Pt = 5.45 nm 0, I [a.u.] -0,0002 f (GHz) Model Equation Reduced Chi-Sqr KittelHaHeb (Use r) y=(((ha+abs(h-h eb))*(ha+abs(h- Heb)+4*M*Pi))^0. 5)*( *g)/(2 *Pi) 1,04239E16-0, H [Oe] 2 1 Adj. R-Square 0, H (Oe) Value Standard Error f Ha 0 0 f Heb 0 0 f M 732, ,23283 f g 2, ,60554

32 ISHE devices ISHE voltage measured on ISHE devices Signal = AMR voltage + ISHE voltage Signal = antisymetric + symetric V ISHE (µv) exp ISHE+AMR ISHE AMR H (Oe) H Spectrum Analyzer V

33 Propagation of magnons Magnon propagation in Al substituted Finemet is of 15 microns. Measurement of S microns VNA-FMR measurements

34 SUMMARY Interface is discontinuous Pt islands up to 1.5 nm SP needs the presence of SO at interfaces Experiment α vs. d(pt) can be described assuming reasonable values of parameters for Pt (E F, k f, λ sd, λ m..) Modulation of Hr to be explained Observation of spin current flow through NiO ISHE measurements in Finemet/Pt devices Gościańska (Finemet, technology); H. Głowiński (experiment & analysis); A. Krysztofik (experiment); J. Barnas(theory); M. Cecot & T. Stobiecki (ISHE)

35 Thank you for your attention! This work has been carried out within Project No. NANOSPIN PSPB-045/2010 supported by a grant from Switzerland through the Swiss Contribution to the enlarged European Union.