Vojtĕch Uhlíř1,2, Stefania Pizzini1, Nicolas Rougemaille1, Zahid Ishaque1, Olivier Fruchart1, Vincent Cros3, Fausto Sirotti4, Erika Jimenez5, Julio Camarero5 et Jan Vogel1
1 Institut Néel, CNRS and UJF, 25 Rue des Martyrs, 38000 Grenoble, France
2 Institute of Physical Engineering, Brno University of Technology, 61669 Brno, Czech Republic
3 Unité Mixte de Physique CNRS/Thales, Route départementale 128, 91767 Palaiseau, France
4 Synchrotron SOLEIL, L’Orme des Merisiers, Saint-Aubin, 91192 Gif-sur-Yvette, France
5 Dept. Física de la Materia Condensada, Univ. Autónoma de Madrid, 28049 Madrid, Spain
Domain walls in magnetic nanowires have been proposed to constitute a new type of fast and cheap magnetic storage medium, the so-called race-track memory [1]. The displacement of the domain walls in these nanowires is induced by short current pulses, through the so-called spin-transfer-torque (STT) effect. Many experimental studies have used magnetic microscopy to investigate current-induced domain wall motion, but all of them used quasi-static measurements, imaging the position and shape of the magnetic domain wall before and after a current pulse. For a better theoretical and experimental understanding of the interaction between spin polarized currents and domain walls it is crucial to directly observe the magnetic configuration of the nanowires during the current pulses.
We have used time-resolved x-ray photoemission electron microscopy (PEEM) to investigate the magnetization dynamics induced by nanosecond current pulses in 300 nm and 400 nm wide NiFe(5nm)/Cu(5nm)/Co(5nm) nanowires [2]. The measurements were carried out at the TEMPO beamline using a pump-probe technique, synchronizing the current pulses injected into the wires with the synchrotron x-ray pulses in the 8-bunch mode. The magnetic images taken during the current pulses directly show, for the first time, that quasi-static and precessional effects are induced by the Oersted magnetic field that is present during the current pulses. This Oersted field induces a large tilt of the NiFe magnetization in the direction transverse to the wire, which may contribute to the increased efficiency of current-induced domain wall motion observed in NiFe/Cu/Co nanowires [3,4].
[1] S.S.P. Parkin, M. Hayashi, and L. Thomas, Science 320, 190 (2008).
[2] V. Uhlíř, S. Pizzini, N. Rougemaille, V. Cros, E. Jiménez, L. Ranno, O. Fruchart, M. Urbánek, G. Gaudin, J. Camarero, C. Tieg, F. Sirotti, and J. Vogel, arXiv:1002.1302v2 [cond-mat.mtrl-sci].
[3] J. Grollier, P. Boulenc, V. Cros, A. Hamzić, A. Vaurès, A. Fert, G. Faini, Appl. Phys. Lett. 83, 509 (2003).
[4] V. Uhlíř, S. Pizzini, N. Rougemaille, J. Novotny, V. Cros, E. Jimenez, G. Faini, L. Heyne, F. Sirotti, C. Tieg, A. Bendounan, F. Maccherozzi, R. Belkhou, J. Grollier, A. Anane, J. Vogel, Phys. Rev. B 81, 224418 (2010).
