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Loss of long-range magnetic order in a nanoparticle assembly due to random anisotropy

By C. Binns, P.B. Howes, S.H. Baker, H. Marchetto, A. Potenza, P. Steadman, S.S. Dhesi, Mervyn Roy, M.J. Everard and A. Rushforth

Abstract

This paper was published as Journal of Physics: Condensed Matter, 2008, 20, 055213. It is available from http://www.iop.org/EJ/abstract/0953-8984/20/5/055213/. Doi: 10.1088/0953-8984/20/5/055213Metadata only entryWe have used soft x-ray photoemission electron microscopy (XPEEM) combined with x-ray magnetic circular dichroism (XMCD) and DC SQUID (superconducting quantum interference device) magnetometry to probe the magnetic ground state in Fe thin films produced by depositing size-selected gas-phase Fe nanoparticles with a diameter of 1.7 nm (~200 atoms) onto Si substrates. The depositions were carried out in ultrahigh vacuum conditions and thicknesses of the deposited film in the range 5–50 nm were studied. The magnetometry data are consistent with the film forming a correlated super-spin glass with a magnetic correlation length ~5 nm. The XPEEM magnetic maps from the cluster-assembled films were compared to those for a conventional thin Fe film with a thickness of 20 nm produced by a molecular beam epitaxy (MBE) source. Whereas a normal magnetic domain structure is observed in the conventional MBE thin film, no domain structure could be observed in any of the nanoparticle films down to the resolution limit of the XMCD based XPEEM (100 nm) confirming the ground state indicated by the magnetometry measurements. This observation is consistent with the theoretical prediction that an arbitrarily weak random anisotropy field will destroy long-range magnetic order

Publisher: Institute of Physics
Year: 2008
DOI identifier: 10.1088/0953-8984
OAI identifier: oai:lra.le.ac.uk:2381/7505
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