Regensburg 2000 – wissenschaftliches Programm

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SYOM: Oberflächenmagnetismus

SYOM 1: Oberflächenmagnetismus I

SYOM 1.3: Vortrag

Dienstag, 28. März 2000, 12:00–12:15, H10

The Spin Density Wave Ground State at the Cr(110) Surface — •Joerg Schaefer¹, Eli Rotenberg¹, and Stephen Kevan² — ¹Advanced Light Source, Lawrence Berkeley National Laboratory, Mailstop 7-222, Berkeley, CA 94720, USA — ²Department of Physics, University of Oregon, Eugene, OR 97403, USA

Spin density waves (SDWs) in the vicinity of a surface take our present understanding of antiferromagnetic exchange coupling to the limit. The SDW in Cr has been studied at the (110) surface using angle-resolved photoemission. This provides, for the first time, direct evidence of the formation of an energy gap in a SDW phase transition at a surface.

Bandmaps intersecting the Fermi surface yield in the antiferromagnetic state i) a backfolding of the electronic bandstructure so far only predicted theoretically, and ii) the occurrence of an energy gap at E_F of ∼200 meV (exceeding the 120 meV in the bulk). A SDW nesting vector of 0.95 Γ-H is inferred. The gap extends with constant magnitude across major parts of the Fermi surface and is matched in position by density functional calculations. From the temperature-dependence of the energy gap, a surface transition temperature of 440 K is determined, considerably above the bulk transition of 311 K. This and the increased energy gap can be understood from the enhanced magnetic moments calculated for the topmost layers. The low critical exponent of 0.38 points at reduced dimensionality behavior near the surface.