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

Homonuclear cobalt and iron clusters CoN and FeN measured in a cryogenic molecular beam exist in two states with distinct magnetic moments (μ), polarizabilities, and ionization potentials, indicating distinct valences. The μ is approximately quantized: μN~2NμB in the ground states and μN*~NμB in the excited states for Co; μN~3NμB and μN*~NμB for Fe. At a large size, the average μ 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.