Spin Mechanics of Ferromagnets

Transcription

1 Spin Mechanics of Ferromagnets Content Gerrit Bauer Gerrit E.W. Bauer Einstein's only experiment Einstein-de Haas effect (1916) B M L Mechanics of Einstein-de Haas effect Barnett effect (1915) ωl, L L L 0 H Barnett ω ω 1

2 Recent experiments Chudo et al. (2014): Barnett-field detection by NMR of rapidly rotating samples. Ganzhorn et al. (2016): Einstein-de Haas effect suppresses quantum tunneling of spin in molecular magnets (cf. theory by Kovalev et al., 2011) 3 Spin mechanics in optics 4 Spin mechanics in transport Magnetoelasticity and striction Magnetic anisotropy couples magnetic and lattice order Magnon-polaritons Kittel (1958) Rücriegel et al. (2014) Kamra et al. (2015) Dynamics E LA TA E - thermalization of lattice and spin - magnon-phonon drift - hybridized states (Kittel, 1958) 0 1/μm magnon 0 Magnetomechanics of nanoparticles Macro-spin & -lattice model Einstein de Haas Total angular momentum: J L M Einstein-de Haas: d L Μ Μ B dt Barnett: ext LLG Bext Banis M Μ M ΜMω M s B ext Newton damping torque Barnett instantaneous rotation axis in lab frame 2

3 Fe sphere with cubic anisotropy Linear response Fe dis Linear response eff 10 4 B m 0 n 0 d = 2 nm = 0.01 FMR 1 2 B m 0 n 0 D = 15 nm, d = 2 nm = 0.01 Yttrium Iron Garnet Y 3 Fe 2 (Fe O 4 (2-) ) 3 A.R. Chahmouradian Yttrium Iron Garnet Y 3 Fe 2 (Fe O 4 (2-) ) 3 80 atoms & 20 magnetic moments/unit cell Spin waves (magnons) d M Landau-Lifshitz equation: MB dt Linearized solution (exchange magnons): 2 2 A 0 - electrical insulator (band gap 2.8 ev) - Curie temperature 550 K - low acoustic damping - high magnetic quality factor Q= large Faraday effect (by doping) - tunable magnetic anisotropy (by doping) Planc (Rayleigh-Jeans) distribution: M M s d v g d magnon 1 T B n T B e 1 3

4 Sublattice model for ferrimagnets Spin waves in magnetite Fe 3 O 4 Acoustic (FMR) mode in eff. magnetic field: B T room Optical (AFM) mode in eff. exchange field: Temperature dependence and chirality red: + chirality blue: - chirality J. Barer & GB (2016) Pump & probe spectrosocpy Femto-second optical excitation Excitation by Inverse Faraday effect Heat Detection by Faraday or Kerr rotation Theory Snapshots (Shen & GB, 2015) 3.45ns Ogawa et al. (2015) Satoh et al. (2012) Hashimoto et al. (unpublished). Ogawa Experiment (Ogawa et al., 2015) Shen & GB (2015) 4

5 Transverse and longitudinal MPs 6.2ns v LT / wave pacage Magnetic field dependence Theory: E LA TA 0 1/μm magnon Experiment by Ogawa et al.: (Longitudinal) spin Seebec effect spin-dependent Seebec effect! V [V] Uchida et al. (2010/2011) Glitches in the SSE (Kiawa et al., 2016) T. Kiawa et al.: experiments B. Flebus, K. Shen et al.: Boltzmann theory Magnon-polaron occupation Planc distributions for two temperatures f (0) () T. Kiawa 5

6 Cross vs. touch (Kiawa et al., 2016) Magnon-polarons in YIG (Kiawa et al., 2016) MEC V V magnon phonon cross point touch point Tae-home messages 1 The FMR of magnetic nanoparticles show low frequency satellites with very high magnetic quality 2 Spin transport in YIG induced by focused lasers is dominated by phonons. 3 The magnon-polaron anomaly in the spin Seebec effect proves strong magnonphonon coupling 4 The acoustic quality of YIG films is better than its magnetic quality. Collaborators Japan Oleg Tretiaov Adam Cahaya Taahiro Chiba Saburo Taahashi Joe Barer Sadamichi Maeawa Yanting Chen Iran Baba Zare Rameshti Hedyeh Keshtgar Sendai Taashi Kiawa Eiji Saitoh Dazhi Hou Koi Taanashi Kenichi Uchida Netherlands Yaroslav Blanter Ka Shen Aash Kamra Sanchar Sharma Simon Streib Rembert Duine Benedetta Flebus Germany Stefan Geprägs Sebastian Gönnenwein c.s. Michael Schreier Mathias Kläui China Peng Yan Yunshan Cao Ke Xia Jiang Xiao Groningen Bart van Wees Ludo Cornelissen 6