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arXiv:1012.4133 · Physical Review Letters

Metastability of Free Cobalt and Iron Clusters: A Possible Precursor to Bulk Ferromagnetism

Xiaoshan Xu, Shuangye Yin, Ramiro Moro, Anthony Liang, John M. Bowlan, Walt A. de Heer

Published Jul 27, 2011• 42 citations
arXivHTMLPDF

Abstract

Homonuclear cobalt and iron clusters ${\mathrm{Co}}_{N}$ and ${\mathrm{Fe}}_{N}$ measured in a cryogenic molecular beam exist in two states with distinct magnetic moments ($\ensuremath{\mu}$), polarizabilities, and ionization potentials, indicating distinct valences. The $\ensuremath{\mu}$ is approximately quantized: ${\ensuremath{\mu}}_{N}\ensuremath{\sim}2N{\ensuremath{\mu}}_{B}$ in the ground states and $\ensuremath{\mu}_{N}{}^{*}\ensuremath{\sim}N{\ensuremath{\mu}}_{B}$ in the excited states for Co; ${\ensuremath{\mu}}_{N}\ensuremath{\sim}3N{\ensuremath{\mu}}_{B}$ and $\ensuremath{\mu}_{N}{}^{*}\ensuremath{\sim}N{\ensuremath{\mu}}_{B}$ for Fe. At a large size, the average $\ensuremath{\mu}$ of the two states converges to the bulk value with diminishing ionization potential differences. The experiments suggest localized ferromagnetism in the two states and that itinerant ferromagnetism emerges from their superposition.

DOI
10.1103/physrevlett.107.057203

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Magnetic properties of DyN{\mathrm{Dy}}_{N}DyN​ clusters in a molecular beam generated with a liquid-helium--cooled nozzle are investigated by Stern-Gerlach experiments. The cluster magnetizations ${\ensuremath{\mu}}_{z}$ are measured as a function of magnetic field (B=0−−1.6(B=0--1.6(B=0−−1.6 T) and cluster size (17< N< 55).(17<~N<~55).(17< N< 55). The most important observation is the saturation of the magnetization ${\ensuremath{\mu}}_{z}(B)$ at large field strengths. The magnetization approaches saturation following the power law $|{\ensuremath{\mu}}_{z}\ensuremath{-}{\ensuremath{\mu}}_{0}|\ensuremath{\sim}1/\sqrt{B},$ where ${\ensuremath{\mu}}_{0}$ denotes the magnetic moment. This gives evidence for adiabatic magnetization.
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