All Acoustic Manipulation and Probing of Spin Ensembles

Transcription

1 All Acoustic Manipulation and Probing of Spin Ensembles Hans Huebl, Sebastian T.B. Goennenwein, Rudolf Gross, Mathias Weiler Walther-Meißner-Institut Bayerische Akademie der Wissenschaften

2 Andrew Davidhazy Mechanical Oscillators beginnersguitarstudio.com Newton, Philosophiae Naturalis Principia Mathematica (1687) Gina Waga (2014) National Geographics Perdue Bashir group (2006) iphone4 gyroscope - Ifixit AFM, Giessibl, Rev. Mod. Phys. 79, 949 (2003)

3 Mechanics with magnetic systems Magnetism Mechanics wondermagnet.com typical classical representation: magnetization vector motional amplitude Gina Waga (2014) quantum effects in large objects

4 Walther-Meißner-Institute Abdi et al., Phys. Rev. Lett. 114, (2015) Weiler et al., Phys. Rev. Lett. 106, (2011) Dreher et al., Phys. Rev. B 86, (2012) Weiler et al., Phys. Rev. Lett. 108, (2012) Pernpeintner et al., J. Appl. Phys. 119, (2016)

5 Strings mechanical resonance frequency r 10μm norm. mechanical response Ω m m L Γ m drive frequency (MHz) nano-string σ tensile stress ( 800 MPa) ρ material density ( 2700 kg/m 3 ) L length of the nanostring ( 30 μm) violine σ tensile stress ( 1200 MPa) ρ material density ( 7800 kg/m 3 ) L length of the string ( 300 mm)

6 Nano-spinmechanics- magnetostriction 10μm Magnetostriction in thin magnetic films Mangon-phonon interaction

7 Magnetic straincontrol dielectric + - P converse magnetoelectric E P inverse piezoelectric magnetoelectric magnetic M ε piezoelectric lattice M H magnetoelastic magnetostrictive σ ε = Δc/c Spaldin & Fiebig, Science 309, 391 (2005).

8 Magnetic straincontrol magnetoelectric magnetic M converse magnetoelectric H M magnetoelastic magnetostrictive dielectric E P + inverse piezoelectric ε - P piezoelectric σ lattice μ 0 H M m r L ε = Δc/c Spaldin & Fiebig, Science 309, 391 (2005).

9 Magnetic straincontrol magnetoelectric magnetic M converse magnetoelectric H M magnetoelastic magnetostrictive dielectric E P + inverse piezoelectric ε - P piezoelectric σ lattice μ 0 H M m r L ε = Δc/c Spaldin & Fiebig, Science 309, 391 (2005).

10 Magnetostriction nanomechanical detection cos $ Φ 10 nm thin magnetic Co film λ = x 10-6 λ = 27.9 x 10-6 λ / comptible with bulk Co Model à technique applicable to ultrathin films only resonance frequency required Pernpeintner et al., J. Appl. Phys. 119, (2016)

11 Magnetic straincontrol magnetoelectric magnetic M converse magnetoelectric H M magnetoelastic magnetostrictive dielectric E P + inverse piezoelectric ε - P piezoelectric σ lattice μ 0 H M m r L ε = Δc/c Spaldin & Fiebig, Science 309, 391 (2005).

12 Dynamic strain magnetization coupling phonons (sound wave) magnon-phonon-coupling (spin-sound-wave) + magnons (spin wave) New physics (e.g. acoustic FMR) Natural mode matching v sound v magnon

13 Ferromagnetic resonance In equilibrium: M H eff H eff external magnetic field Dynamics: Landau-Lifshitz- Gilbert equation H eff H eff t m = γm μ 0 H eff +a m t m γ: gyromagnetic ratio a : damping parameter precession damping H eff M M M equilibrium M excitation dynamic relaxation time equilibrium

14 Ferromagnetic resonance excitation schemes (microwave) photon-driven ferromagnetic resonance phonon-driven ferromagnetic resonance ω 9:; = γμ = H :?? h A (t) = h A cos(ω DEF t) real, external magnetic driving field H GHI:J (t) = H GHI:J cos(ω DEF t) virtual, internal magnetic driving field this talk

15 Ferromagnetic resonance free energy μ = H eff = mf VW effective magnetic field F VW = μ = H m+b` u m $ $ + B a m c Zeeman term in-plane anisotropy 2B^ 10 mt shape anisotropy 2B [ 1T in-plane F DC contour m = M/M s u: unit vector shape anisotropy in-plane anisotropy M: magnetization H: external magnetic field M direction: along min(f DC )

16 Surface acoustic waves (SAWs) Nickel/Cobalt thin film LiNbO 3 substrate Surface acoustic wave Magnetoelastic coupling k SAW ε<0 ε>0 x rf strain ε(t) 10-5 along x velocity 3500 m/s (λ SAW =20μm, f=175 MHz)

17 Magnetoelastic drive μ = H GHI:J = m F ef F ef (t) = B A ε h (t)m h $ magnetoelastic coupling constant ( 20 T) strain ( 10-5 ) Pure strain ε along x Magnetoelastic material (B 1 0): Nickel thin film radio frequency strain ε: surface acoustic wave ε h > < 0

18 rotatable Electromagnet: µ 0 H 1 T Port 2 Aluminium Aluminium 200μm Nickel SAW LiNbO 3 Port 1 VNA: measure complex S 21 (transmitted SAW power and phase) micrograph of actual sample Weiler et al., Phys. Rev. Lett. 106, (2011) & Dreher et al., Phys. Rev. B 86, (2012)

19 Microwave transmission 0 S 21 (db) st = 172 MHz 5 th H=0 7 th 9 th Frequency (GHz) Several SAW transmission maxima Weiler et al., Phys. Rev. Lett. 106, (2011) & Dreher et al., Phys. Rev. B 86, (2012)

20 0 S 21 (db) st = 172 MHz 5 th 7 th 9 th Frequency (GHz) S 21 (db) α=30 no FMR 7mT FMR 100mT Frequency (GHz) strong change in SAW transmission as a function of magnetic field strength! Δ S 21 (7mT)=-5 db y H SAW α x in-plane magnetic field Weiler et al., Phys. Rev. Lett. 106, (2011) & Dreher et al., Phys. Rev. B 86, (2012)

21 Acousticferromagnetic resonance S 21 - S mT (db) GHz upsweep Δ S 21 (7mT) = S 21 (7mT)- S 21 (150mT) =-5 db α= µ 0 H (mt) Weiler et al., Phys. Rev. Lett. 106, (2011) & Dreher et al., Phys. Rev. B 86, (2012)

22 Acousticferromagnetic resonance S 21 - S mT (db) GHz Acoustic ferromagnetic resonance! upsweep downsweep α= µ 0 H (mt) Weiler et al., Phys. Rev. Lett. 106, (2011) & Dreher et al., Phys. Rev. B 86, (2012)

23 Acousticferromagnetic resonance S 21 (db) S 21 - S mT (db) 1 st = 172 MHz 0.17 GHz GHz GHz GHz th 9 th 7 th Frequency (GHz) µ 0 H (mt) α=30 ω 9:; = γμ = H :?? Weiler et al., Phys. Rev. Lett. 106, (2011) & Dreher et al., Phys. Rev. B 86, (2012)

24 Acousticferromagnetic resonance GHz Color code: S 21 ɸ 0 =90 ɸ 0 =30 in-plane magnetic field H k SAW α H SAW α ( ) 0 ɸ 0 =0 H k SAW µ 0 H (mt) ɸ 0 =-90 H k SAW Weiler et al., Phys. Rev. Lett. 106, (2011) & Dreher et al., Phys. Rev. B 86, (2012)

25 Comparison: Measurement vs. simulation Measurement Pabs Simulation Measurement Pdisp u=x Bu=2.5 mt Bd=400 mt B1=25 T Ms=370 ka/m a=0.1 quantitative Simulation no further parameters Simulation in-plane rotation ε (measured) Weiler et al., Phys. Rev. Lett. 106, (2011) & Dreher et al., Phys. Rev. B 86, (2012)

26 Spin pumping in a nutshell V J s s 3 Detection: Inverse spin Hall effect J c = α 2e SHE ħ J s s α SHE : Spin Hall angle α SHE 0.01 (Pt) 2 Relaxation (Spin pumping contribution) J s = ħ 4π g m t m J s ħν 2 g sin $ Θ 1 Ferromagnetic resonance F. Czeschka, PhD thesis, TUM (2011) t m = γm μ 0 H eff +a m t m

27 Acousticly driven spin pumping / time domain P rf =+30 dbm Raw data Field dep. P IDT (mw) ΔP IDT (µw) EMW EMW P(µ 0 H)-P(µ 0 H ref ) µ 0 H ref =30mT SAW +4mT SAW +30 mt t (µs) -4mT V DC (mv) ΔV DC (µv) α=10 Weiler et al., Phys. Rev. Lett. 108, (2012) EMW EMW µ 0 H ref =30mT SAW V(µ 0 H)-V(µ 0 H ref ) +4mT SAW t (µs) -4mT Separation of EMW-driven and SAW-driven contributions EMW: Speed of light SAW: Speed of sound

28 Acousticly driven spin pumping a ΔP IDT (µw) b ΔV DC (µv) 0 FMR -2-4 t=0.7 μs SAW t=0.6 μs MSP V dc M J s µ 0 H (mt) Weiler et al., Phys. Rev. Lett. 108, (2012) ΔP IDT (µw) ΔV DC (µv) 0 +4mT -2 EMW SAW -4-4mT -6 4 SAW 2 +4mT 0 EMW -2-4mT t (µs)

29 Acknowledgements Lukas Dreher Martin S. Brandt Mehdi Abdi Michael Hartmann Nano-Mechanics Matthias Pernpeintner Achim Marx Philip Schmidt Daniel Schwienbacher Friedrich Wulschner Fredrik Hocke Rasmus Holländer Anh Tu Bohn Magnetiker Franz Czeschka Christian Heeg Frederik S. Goerg Matthias Opel Stephan Geprägs

30 Summary Sensing magnetoelastics in nanostructures Acousticly driven ferromagnetic resonance Acousticly driven spin pumping ΔP IDT (µw) ΔV DC (µv) EMW EMW +4mT SAW -4mT SAW +4mT -4mT t (µs)