Spin Mechanics of Ferromagnets

Transcription

1 Spin Mechanics of Ferromagnets Content Gerrit Bauer Gerrit E.W. Bauer Einstein's only experiment 3 Yttrium Iron Garnet (YIG) 4 Spin mechanics in optics 5 Spin mechanics in transport Einstein-de Haas effect (1916) B M Mechanics of Einstein-de Haas effect Barnett effect (1915) ω, 0 0 H Barnett ω ω 1

2 Freely suspended magnetic wire Collectie coordinate approximation ext m x, t ext r w x r w x andau-ifshitz-gilbert & Newton equations: m mh e eff x m m I m mech ext mag mech external and internal magnetic fields magnetic friction mechanical friction w ext w w ww AM sh ext Onsager: w w EdH Barnett Recent experiments Chudo et al. (014): Barnett-field detection by NMR of rapidly rotating samples. Ganzhorn et al. (016): Einstein-de Haas effect suppresses quantum tunneling of spin in molecular magnets (cf. theory by Koale et al., 011) Spin mechanics Magnetic anisotropy couples magnetic and lattice order Magnon-polaritons Kittel (1958) Rückriegel et al. (014) Kamra et al. (015) Dynamics E A TA E - thermalization of lattice and spin - -phonon drift - hybridized states (Kittel, 1958) 0 1/μm k 0 k

3 Cf. poster by Hedyeh Keshtgar and Simon Streib Magnetomechanics of nanoparticles Total angular momentum: J M Einstein-de Haas: d Μ ΜB dt Barnett: dm dm MB M dt M M ω dt s B G Einstein de Haas Newton damping torque Barnett instantaneous rotation axis in lab frame Fe sphere with cubic anisotropy FMR inear response eff 10 4 Fe disk inear response B m 0 n 0 d = nm = 0.01 FMR 1 B m 0 n 0 D = 15 nm, d = nm = 0.01 Pump & probe spectrosocpy Femto-second optical excitation Excitation by Inerse Faraday effect Heat Detection by Faraday or Kerr rotation Ogawa et al. (015) Satoh et al. (01) Hashimoto et al. (unpublished). Ogawa 3

4 Snapshots 3.45ns Theory Experiment (Ogawa et al., 015) 6.ns 6.ns TA A Shen & GB (015) (ongitudinal) spin Seebeck effect Glitches in the SSE (Kikkawa et al., 016) V [V] T. Kikkawa & E. Saitoh: experiments B. Flebus & K. Shen: Boltzmann theory Uchida et al. (010/011) Magnon-polaron occupation Cross s. touch (Kikkawa et al., 016) two Planck distributions MEC T. Kikkawa phonon cross point touch point 4

5 Magnon-polarons in YIG (Kikkawa et al., 016) Take-home messages phonon The FMR of magnetic nanoparticles show should hae ery sharp low frequency satellites. Spin transport in YIG induced by focused lasers is dominated by phonons. 3 The -polaron anomaly in the spin Seebeck effect indicates better mechanical than magnetic quality of YIG films. Collaborators Japan Oleg Tretiako Adam Cahaya Takahiro Chiba Saburo Takahashi Joe Barker Sadamichi Maekawa Yanting Chen Iran Babak Zare Rameshti Hedyeh Keshtgar Sendai Takashi Kikkawa Eiji Saitoh Dazhi Hou Koki Takanashi Kenichi Uchida Netherlands Yarosla Blanter Ka Shen Akash 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 an Wees udo Cornelissen 5