Proximity Magnetism and Spin-Hall Anomalous Hall Effect in Pt on Y 3 Fe 5 O 12 (YIG) Sibylle Meyer 1 , Richard Schlitz 1 , Stephan Geprägs 1 , Matthias Opel 1 , Fabrice Wilhelm 2 , Katharina Ollefs 2 , Andrei Rogalev 2 , Sebastian T.B. Goennenwein 1,3 , Rudolf Gross 1,3,4 1 Walther - Meißner - Institut (WMI), Bayerische Akademie der Wissenschaften , 85748 Garching , GERMANY 2 European Synchrotron Radiation Facility (ESRF), 38043 Grenoble Cedex 9, FRANCE 3 Nanosystems Initiative Munich (NIM), 80799 München, GERMANY 4 Physik - Department, Technische Universität München (TUM), 85748 Garching, GERMANY www.wmi.badw.de International Workshop on Oxide Electronics (Paris, 2015), P47 www.wmi.badw.de 2 4 6 -100 -50 0 50 B (pm) μ 0 H (T) 50 100 150 Pt(3.1nm)|YIG A (pm) Pt(2.0nm)|YIG Spin Currents resonant excitation theory: Tserkovnyak, PRL 88 , 117601 (2002) expt.: Mosendz, PRL 104 , 046601 (2010) scaling: Czeschka, PRL 107 , 046601 (2011) FMM: Uchida, Nature 455 , 778 (2008) FMI: Uchida, Nature Mater. 9 , 894 (2010) DMS: Jaworski, Nature Mater. 9 , 898 (2010) local SSE: Weiler, PRL 108 , 106602 (2012) thermal excitation Transport of Angular Momentum, No Moving Charges spin current normal metal NM ferromagnet FM magnons spin current detection → via inverse spin-Hall effect (iSHE) in normal metal (NM) problem → conductivity of the ferromagnet (FM) solution → use ferromagnetic insulators (FMI) Laser-MBE of Y 3 Fe 5 O 12 Thin Films substrate IR heating laser and pyrometer 140 W, 938 nm RHEED screen UV excimer laser 248 nm target carousel zoom optics plasma plume target PLD parameters substrate: Y 3 Al 5 O 12 (111) (YAG) target: Y 3 Fe 5 O 12 (YIG) fluence: 2 J/cm 2 rep. rate: 10 Hz temperature: 500°C atmosphere: 2.5×10 -2 mbar O 2 thickness: ~ 60 nm 20 nm, 10 nm, 7 nm, 3 nm, 1.6 nm Pt by in-situ electron-beam evaporation 60 nm YIG(111) by pulsed laser deposition (PLD) SUB YAG(111) lattice mismatch = 3% Y 3 Fe 5 O 12 (111) FM insulator Pt normal metal Y 3 Al 5 O 12 (111) substrate PLD target PLD plasma plume 10 mm In-situ Thin Film Deposition via PLD (Y 3 Fe 5 O 12 ) and Electron-Beam Evaporation (Pt) -5000 0 5000 -200 -100 0 100 200 no Pt 3 nm Pt 7 nm Pt 10 nm Pt 0 H (mT) M (kA/m) Pt/YIG 300 K -20 0 20 0 H (mT) M (kA/m) 4 NM|FMI samples Pt|Y 3 Fe 5 O 12 on Y 3 Al 5 O 12 NM|FMM reference sample Pt|Fe on Y 3 Al 5 O 12 -100 -50 0 50 100 -1000 -500 0 500 1000 no Pt 10 nm Pt 0 H (mT) Pt/Fe 300 K YIG bulk SQUID Magnetometry SQUID results magnetization of Pt|Y 3 Fe 5 O 12 close to Y 3 Fe 5 O 12 bulk value of 143 kA/m excellent magnetic quality Pt|Fe sample for comparison Geprägs et al., Appl. Phys. Lett. 101 , 262407 (2012) XRD results epitaxial, oriented growth no secondary phases detectable low mosaic spread FWHM = 0.1° for YIG(444) X-Ray Diffraction (XRD) ω-2θ scan 20° 40° 60° 80° 100° 120° 10 1 10 2 10 3 10 4 10 5 10 6 10 7 10 8 * * I (cps) 2 YIG (888) YAG (888) Y 3 Fe 5 O 12 on Y 3 Al 5 O 12 * 50° 51° 52° 53° 54° 10 1 10 2 10 3 10 4 10 5 YIG (444) YAG (444) Althammer et al., Phys. Rev. B 87 , 224401 (2013) Pt and Yttrium Iron Garnet (Y 3 Fe 5 O 12 ) FMI: Y 3 Fe 5 O 12 (y ttrium i ron g arnet, YIG) NM: Pt (large spin-Hall angle) Y 3 Fe 5 O 12 (YIG) ferrimagnetic due to Fe 3+ ions high Curie temperature T C = 560 K electrically insulating Nakayama et al., PRL 110 , 206601 (2013) -40 -20 0 20 40 408.7 408.8 408.9 long (nm) Althammer et al., PRB 87 , 224401 (2013) -20 -10 0 10 20 -150 -100 -50 0 50 100 150 M (kA/m) 0 H (mT) Experimental observations magnetic hysteresis in ferrimagnetic Y 3 Fe 5 O 12 magnetoresistance effect in non -magnetic Pt magnetic proximity effect? Spin-Hall Magnetoresistance (SMR) in Pt on Y 3 Fe 5 O 12 (YIG) Spin -Hall Effect in Pt spin separation Spin Current J s perpendicular to S and J q ⇓ Spin Accumulation at the interface to YIG ⇓ Spin Absorption by YIG via spin-transfer torque (STT) ⇓ Dissipation of spin current J s ⇓ Increase of Electrical Resistivity ρ in Pt ⇓ Pt Y.-T. Chen et al., Phys. Rev. B 87 , 144411 (2013) YIG ONLY IF M ⊥ s Althammer et al., PRB 87 , 224401 (2013) Nakayama et al., PRL 110 , 206601 (2013) j C j S s Novel SMR effect: SMR = 0 − 1 2 m t = transverse component of M (along s) Conventional (polycrystalline) AMR effect: AMR = 0 + Δ 2 m j = longitudinal component of M (along j c ) -90° 0° 90° 180° 270° 406.5 406.6 406.7 (nm) 300 K 1 T experimental data SMR simulation (m t = sin β, ρ ∝ sin 2 β) AMR simulation (m j = 0) photo- lithography rotating magnetic field h absorption of spin current reflection of spin current absorption of spin current Compound Whiteline Intensity ("XAS step height") PtO 1.6 2.20 a.u. PtO 1.36 1.50 a.u. Pt 1.25 a.u. Temperature Dependence of the SMR SMR Amplitude in Pt|Y 3 Fe 5 O 12 Temperature/thickness dependence SMR model 0 5 10 15 20 3.0x10 -4 6.0x10 -4 9.0x10 -4 1.2x10 -3 3.0x10 -4 6.0x10 -4 9.0x10 -4 1.2x10 -3 3.0x10 -4 6.0x10 -4 9.0x10 -4 1.2x10 -3 50K 20K 10K t (nm) 150K 100K 75K 300K 250K 200K − 1 0 = 2 SH 2 2 ↑↓ tanh 2 1+2 ↑↓ coth Y.-T. Chen et al., Phys. Rev. B 87 , 144411 (2013) Pt resistivity: ρ Pt thickness: t Pt spin diffusion length: λ ≃ 1.5 nm Pt spin-Hall angle: α SH ≃ 0.08 … 0.11 Spin mixing interface conductance: G ↑↓ ≃ 4×10 14 Ω -1 m -2 Meyer et al., Appl. Phys. Lett. 104 , 242411 (2014) Results from fits Result SMR max. for Pt Thickness ≈ Spin Diffusion Length Summary This work was supported by the ESRF via HE-3784, HC-1500 and the DFG via priority program SPP 1538 High -quality epitaxial Y 3 Fe 5 O 12 (YIG) thin films via pulsed laser deposition on Y 3 Al 5 O 12 (YAG) substrates In -situ e-beam evaporation of thin Pt layers (1.6, 3, 7, 10 nm) XANES at Pt L 2,3 edges compatible with metallic Pt on Y 3 Fe 5 O 12 No indication for oxidation of Pt → high interface quality Finite XMCD for Pt|Fe (FMM), no XMCD for Pt|Y 3 Fe 5 O 12 (FMI) No indication for magnetic proximity effect in Pt on Y 3 Fe 5 O 12 Spin -Hall angle for Pt ≃ 0.08 … 0.11 Spin -Hall anomalous Hall effect with higher order contributions S. Meyer et al., Appl. Phys. Lett. 104 , 242411 (2014). S. Meyer et al., Appl. Phys. Lett. 106 , 132402 (2015). M. Althammer et al., Phys. Rev. B 87 , 224401 (2013). H. Nakayama et al., Phys. Rev. Lett. 110 , 206601 (2013). Y.M. Lu et al., Phys. Rev. Lett. 110 , 147207 (2013). Y.-T. Chen et al., Phys. Rev. B 87 , 144411 (2013). S. Geprägs et al., arXiv:1307.4869 (2013). S. Geprägs et al., Appl. Phys. Lett. 101 , 262407 (2012). Hall Measurements in Pt|Y 3 Fe 5 O 12 Results Ordinary Hall effect (OHE) changes sign for thin Pt Anomalous Hall effect (AHE) increases for thin Pt Higher order contributions to AHE Meyer et al., Appl. Phys. Lett. 106 , 132402 (2015) Spin-Hall Anomalous Hall Effect (SH-AHE) trans = − 2 m n = normal component of M (along n) 2 = 2 SH 2 2 Im ↑↓ tanh 2 2 −1 +2Re ↑↓ coth 2 trans = sin + sin 3 -2 0 2 -80 -40 0 40 80 -2 0 2 -2 0 2 0 H (T) Pt(19.5nm)|YIG trans (pm) = 90° Pt(6.5nm)|YIG Pt(2.0nm)|YIG 2 AHE 0° 180° 360° -20 -10 0 10 20 trans (pm) 2T 4T 7T Pt(3.1nm)|YIG -20 -10 0 10 20 0 5 10 15 20 -10 0 10 20 Pt|YIG 10K 100K 300K A OHE (pm/T) Pt thickness t (nm) SH-AHE theory ImG = -3x10 13 -1 m -2 A AHE (pm) ImG = 1x10 13 -1 m -2 Pt L 2 edge: 2p 1/2 → 5d 13273 eV L 3 edge: 2p 3/2 → 5d 11564 eV Comparison with Lu et al. X-Ray Magnetic Circular Dichroism (XMCD) XANES results for Pt metallic Pt layer no indication for oxidation or intermixing with Y 3 Fe 5 O 12 Geprägs et al., arXiv:1307.4869 (2013) & Appl. Phys. Lett. 101 , 262407 (2012) XANES and XMCD in Pt|Fe 11540 11560 11580 11600 -1.00 -0.75 -0.50 -0.25 0.00 0.25 0.50 0.75 1.00 1.25 XMCD x100 Pt(10nm)/YIG Pt(10nm)/Fe Photon energy (eV) norm. intensity (a.u.) XANES = 0.03 μ B /Pt Pt|Fe: m s = 0.03 μ B /Pt consistent with literature values for Pt|Ni, etc… 1.25 11560 11580 11600 13250 13300 13350 0.0 0.5 1.0 1.5 * * L 2 edge norm. XANES (a.u.) 295 K 0.6 T Pt(1.6nm)/YIG Pt L 3 edge -1.0% -0.5% 0.0% 0.5% 1.0% 1.5% 2.0% XMCD 11540 11560 11580 11600 -0.50 -0.25 0.00 0.25 0.50 0.75 1.00 1.25 Pt(3nm)/YIG Pt(7nm)/YIG Pt(10nm)/YIG norm. intensity (a.u.) Photon energy (eV) XANES XMCD x100 < 0.003 μ B /Pt Normalized XANES and XMCD in Pt|Y 3 Fe 5 O 12 from integrated XMCD signal: Pt|Y 3 Fe 5 O 12 : m s < 0.003 μ B /Pt 1.25 1.25 EXAFS wiggle EXAFS wiggle Pt L 3 normalized whiteline intensity ~1.25 a.u. → compatible with metallic Pt EXAFS wiggles at ~11587 eV and ~13299 eV → characteristic for Pt metal Kolobov et al., APL 86 , 121909 (2005) Our XMCD results XMCD for Pt on Fe XMCD for Y 3 Fe 5 O 12 on Pt (“inverted” bilayer) BUT: no finite XMCD for Pt on Y 3 Fe 5 O 12 no magnetic proximity effect for Pt on Y 3 Fe 5 O 12 XANES whiteline intensities 11550 11580 11610 13260 13290 13320 13350 0.0 0.5 1.0 1.5 -1% 0% 1% 2% L 2 edge norm. XANES (a.u.) Photon Energy (eV) 295 K 0.6 T Pt(1.6nm)/YIG YIG/Pt(10nm) Pt L 3 edge XMCD Normalized XANES and XMCD in „inverted“ Y 3 Fe 5 O 12 |Pt = 0.037 μ B /Pt 1.25 EXAFS wiggle EXAFS wiggle from sum rules: Pt|Y 3 Fe 5 O 12 : m s = 0 Y 3 Fe 5 O 12 |Pt: m s = 0.037 μ B /Pt Pt L 3 normalized whiteline intensity ~1.25 a.u. → compatible with metallic Pt EXAFS wiggles at ~11587 eV and ~13299 eV → characteristic for Pt metal intermixing with/incorporation into Y 3 Fe 5 O 12 due to high energy of PLD particles? European Synchrotron Radiation Facility (ESRF) Beamline ID12 Lu, …, Chien, PRL 110 , 147207 (2013) 2.07 XAS/XMCD investigation of only one single sample XAS whiteline = 2.07 no EXAFS wiggles detected strong indication for non-metallic Pt MPMR explanation questionable for Pt on Y 3 Fe 5 O 12 Lu et al., Phys. Rev. Lett. 110 , 147207 (2013) Lu et al. report XMCD for Pt on Y 3 Fe 5 O 12 , BUT: Pt(1.5 nm)|YIG: m s = 0.054 μ B /Pt @300K YIG: LPE-grown, Pt: ex-situ sputtered