Untersuchung des Spin - Reorientierungsübergangs in ultradünnen Filmen und Nanostrukturen mittels spinaufgelöster Rastertunnelmikroskopie
Final Report Abstract
Magnetic contrast of Fe/Mo(110) nanowires was observed using tungsten tips covered by Au/Co thin films. Due to the spin reorientation transition of Co films on Au an out-of-plane magnetic sensitivity is obtained for tips with thin cobalt films up to 8 monolayers (ML) of Co, while for thicker Co coverage an in-plane magnetization component can be probed. At the lowest temperature (5 K), a single Fe monolayer (ML) and a double layer (DL) of Fe on Mo(llO) show perpendicular magnetization. An in-plane easy axis has been observed for structures equal or thicker than 3 ML with an atomically sharp transition ofthe easy axis. A coverage of one ML Au on the Fe/Mo(110) monolayer changes the easy axis fi-om out of plane to in-plane. This transition occurs for coverage larger than 0.1 ML Au as a discontinuous transition involving the complete system. Post-deposition-annealing at 700 K results in the formation of circular shaped double layer islands with perpendicular magnetization in the centre of monolayer patches consisting of a homogeneous paramagnetic AuFe alloy. Using spin-polarized spectroscopy the transport spin polarization through the Au ML could be determined. A statistical analysis of the magnetization direction in the DL islands reveals a coupling through the substrate and the surrounding AuEe ML.This-lateraL indirect exchange coupling outbalances the antiparallel dipolar coupling at distances closer than 5 nm. For the clear case of the DL Fe/Mo(110) with perpendicular magnetization at 5 K the temperature dependence ofthe magnetic anisotropy was measured in detail. We observed a temperature-driven spin-reorientation transition. Magnetization components along the vertical and horizontal directions were detected separately using the spin reorientation transition in the tip for thin and thick Co coverage. For Fe DL nanostripes, the magnetic easy axis of the Fe DL continuously rotates from the vertical direction at 5 K to an in-plane direction at 20 K. The rotation angle is independent on the width ofthe Fe DL nanowires. Both out-of-plane and in-plane magnetic asymmetries show a strong decrease at the SRT. In contrast the asymmetry remains constant in the case of area-like Fe DL structures. In order to investigate the anisotropy change we investigated the domain wall width in the Fe ML and DL as a function of temperature. A different behaviour for different domain wall orientations indicates an orientation dependent magnetic anisotropy with the result of a nearly temperature-independent anisotropy and a sudden change ofthe easy axis at the SRT. The change of the pre-amplifier and the corresponding cables in the vacuum part of the STM required a factory reassembling of the whole system which was conducted at the start of the funding period. The new pre-amplifier enables a considerable reduction of capacitive over talk. The tunnelling current can now be changed in a much wider range than before. Due to the improved noise performance of the pre-amplifier tunnelling spectroscopy shows more reproducible results. Conductivity maps can be measured directly from the current versus voltage measurement without modulation enabling a faster data acquisition.
Publications
- Magnetic Anisotropies and Coupling Mechanisms in Fe/Mo(lJO) Nanostripes. Phys. Rev. Lett. 95, 2005,187202
J. Prokop, A. Kukunin, H. J. Elmers
- Magnetic Properties of laterally confined ultrathin fdms IBM research center, Rüschlikon, Switzerland, 13. December 2006
Hans-Joachim Elmers
- Properties of ultrathin alloy fdms -frontiers of magnetic storage density Trinity College Dublin, Ireland, 08. November 2006
Hans-Joachim Elmers
- Properties of Ultrathin Alloy Films: Frontiers of magnetic Storage Density 2. Physikalisches Institut B, RWTH Aachen (Germany), 4 May 2006
Hans-Joachim Elmers
- Spin-polarized scanning tunneling microscopy and spectroscopy of ultrathin Fe/Mo(110) films using W/Au/Co tips. Phys. Rev. B 73, 2006, 014428
J. Prokop, A. Kukunin, H. J. Elmers
- Spin-polarized scanning tunneling microscopy and spectroscopy ofFe(110)/Mo(110) nanostructures 4th International Conference on Scanning Probe Spectroscopy, Hamburg, 25. Juli 2006
Hans-Joachim Elmers
- Spin-polarized Scanning Tunneling Microscopy of Ultrathin Films. Acta Phys. Pol. A 109, 2006, 371
A. Kukunin, J. Prokop, H. J. Elmers
- A view on ferromagnetism on the atomic level: spin-polarized scanning tunneling microscopy and spectroscopy Physikalisches Kolloquium, Bielefeld, 4. October 2007
Hans-Joachim Elmers
- Komplexität hilft - Neue Materialien fur die Spintronik PhysikalischesKolloquium, TU Chemnitz, 18. April 2007
Hans-Joachim Elmers
- Reconstructed bcc Co films on the Cr(l110)/W(1 10) surface, Surf Sci. 601, 2007, 5026
T. Methfessel and H. J. Elmers
- Spin-polarized tunneling spectroscopy and magnetic coupling in Au-coated Fe/Mo(110) nanostructures. Phys. Rev. B 75, 2007, 144423
J. Prokop, A. Kukunin, and H. J. Elmers
- Spinpolarized current through a Au monolayer Drei-Königstreffen, Bad Honnef, 06. January 2007
Hans-Joachim Elmers
- Structural, electronic, and magnetic properties of pseudomorphic CrFe nanostripes on W(110). Phys. Rev. B 75, 2007, 184419
T. Methfessel, M. Pratzer, and H. J. Elmers
- Structure and magnetism on a nanoscale Seeheim Conference on Magnetism, Seeheim, 26.August 2007
Hans-Joachim Elmers
- Temperature-driven spin reorientation transition in Fe/Mo(110) nanostructures. Phys. Rev. B 76, 2007, 134414
A. Kukunin, J. Prokop, and H. J. Elmers
- Temperature dependence of magnetic properties in 2-dimensional systems and in complex compounds Eindhoven, Netherlands, 08. June 2008
Hans-Joachim Elmers
- Morphology and electronic structure of bcc Co(110) and fcc/hcpCo(111) on Fe(1 10) investigated by STM and STS. Surf Sci. 603. 2009, 462
T. Methfessel and H.J. Elmers
