Nd(0001): a spin glass with a twist?

  • Datum:
  • Plats: Ångströmlaboratoriet Å1203 (Fakultetsrummet)
  • Föreläsare: Prof. Dr. Alexander A. Khajetoorians
  • Kontaktperson: Diana Iusan
  • Seminarium

Scanning Probe Microscopy Department, Institute for Molecules and Materials, Radboud University, Nijmegen, The Netherlands

Spin-resolved scanning tunneling spectroscopy (SP-STM/SP-STS) has been a powerful methodology, which can reveal magnetic order with unprecedented spatial and energy resolution. SP-STM has been successfully applied to reveal the changes in magnetic order in single layer 3d transition metal films on a variety of 5d transition metal surfaces, revealing non-collinear or skyrmionic order [1, 2]. Unlike 3d transition metals, lanthanide metals can exhibit complex magnetic structures, resulting from different mechanism, compared to 3d transition metals. Neodymium (Nd) shows the most complicated behavior exhibiting several magnetic phase transitions below TN = 19.9 K, resulting in a multi-q structure according to interpretations based on magnetic neutron or X-ray diffraction experiments [3]. However, as these techniques lack spatial resolution, the variations in magnetic properties of Nd, as well as a deeper understanding of this ordering, at the atomic length scale are still unexplored. The local surface electronic structure of Nd(0001) has been studied only using spin-integrated STS [4,5]. In this talk, I will review the basis of SP-STM and its application to study magnetic order via the surface of thin magnetic films. I will then present ultra-low temperature SP-STM measurements of bulk-like Nd(0001) films grown on W(110), in magnetic fields. The most fascinating discovery is the observation of a new type of magnetic ordering on the surface of Nd(0001), previously unobserved. We observe multi-q magnetic behavior on the surface as evidenced by strong short-range order, but without the existence of long-range order. Magnetic field and temperature dependent measurements reveal high sensitivity of the spectral weight of q-states, without any clear unique ground state, as well as evidence of an aging-like behavior. We discuss our findings in the context of unconventional spin-glass behavior.

[1] M. Bode et al., Nature, 447, 190 (2007)
[2] S. Heinze et al., Nature Physics, 7,713 (2011)
[3] R. M. Moon & R. M. Nicklow, J. Magn. Magn. Mater. 100, 139 (1991)
[4] D. Wegner et al., Phys. Rev. B 73, 165415 (2006)
[5] D. Wegner et al., Jpn. J. Appl. Phys. 45, 1941 (2006)