Regensburg 2000 – wissenschaftliches Programm

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AM: Magnetismus

AM 13: Postersitzung: Dünne Schichten (1–22), Magnetowiderstand (23–40), Phasenübergänge (41–55), Mikromagnetismus (56–68), Spektroskopie (69–77), Nanokristalline Materialien (78–82), Anisotropie (83–86), Schmelzen (87–90), Weitere Bereiche (91–100)

AM 13.39: Poster

Dienstag, 28. März 2000, 16:00–20:00, A

A Simple Model for Ultrasmall Ferromagnetic Grains with Discrete Energy Levels — •Silvia Kleff and Jan von Delft — Institut für Theoretische Festkörperphysik, Universität Karlsruhe, 76128 Karlsruhe

We propose a simple model to describe ultrasmall ferromagnetic grains with discrete energy levels. The discrete spectrum of such grains was recently measured using single-electron tunneling spectroscopy [1]. These experiments allow the effects of an applied magnetic field H on a particle to be studied in unprecedented detail, since they reveal the H-dependence of individual eigenenergies, including what happens when the magnetization undergoes sudden, hysteretic changes. We propose what we would like to regard as the “simplest possible non-trivial yet sensible toy model” for an ultrasmall metallic grain made from a material that exhibits itinerant ferromagnetism (Co, Ni and Fe are the prime examples) in which the itinerant conduction electrons in the s, p and d bands of Co are treated explicitly, and not just their total spin S^→. Within this framework we take into account recent experiments which indicate a strong influence of the barrier on whether the tunneling current is carried by s or d electrons [2,3]. We use our model to make qualitative predictions for the tunneling spectrum and compare it to the measured ones.

[1] S. Guéron et al., [cond-mat/9904248]

[2] J.M. De Teresa et al., Science 286, 507 (1999)

[3] R. Meservey and P.M. Tedrow, Phys. Rep. 238, 173 (1994)