Berlin 2008 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 29: Spin Structures / Magnetic Phase Transitions

MA 29.3: Vortrag

Donnerstag, 28. Februar 2008, 18:15–18:30, H 1012

Direct Experimental Observation of Fermi-Surface Nesting in Tb and Dy Metal — •Kristian Döbrich¹, Aaron Bostwick², Kai Rossnagel², Jessica McChesney², Eli Rotenberg², and Günter Kaindl¹ — ¹Institut für Experimentalphysik, Freie Universität Berlin, Germany — ²Advanced Light Source, Lawrence Berkeley National Laboratory, UC Berkeley, USA

Some of the lanthanide metals develop antiferromagnetic phases with a helical arrangement of the localized 4f electron spins. The magnetic coupling is mediated by the valence electrons (RKKY interaction). The commonly accepted nesting hypothesis links the formation of helical ordering to the existence of parallel sheets of the Fermi surfaces (FS), the so-called FS nesting. For Y and Y-Gd alloys, FS nesting was observed with positron annihilation. However, for a pure lanthanide metal, nesting had not been observed prior to this work.

Angle-resolved photoemission as performed at beamline 7.0.1 of the Advanced Light Source, Lawrence Berkeley National Laboratory, USA, gives access to the occupied part of the electronic structure over a wide region of momentum space, covering several Brillouin zones. We studied Gd metal that orders ferromagnetically as well as the two metals Tb and Dy, which exhibit helically-ordered antiferromagnetic phases. The photoemission data on Gd presented here confirm the absence of FS nesting in this metal, while our data on Tb and Dy give clear evidence of FS nesting in these two metals. The present results therefore provide strong support for the correctness of the nesting hypothesis.

This work was supported by the DFG project No. STA 413/3-1.