AVS 53rd International Symposium
    Magnetic Interfaces and Nanostructures Tuesday Sessions
       Session MI-TuM

Paper MI-TuM6
Single Domain and Vortex State Phase Fractions in Arrays of sub-100nm Fe Nanodots*

Tuesday, November 14, 2006, 9:40 am, Room 2006

Session: Magnetic Nanostructures, Nanoparticles and Interfaces
Presenter: R.K. Dumas, University of California - Davis
Authors: R.K. Dumas, University of California - Davis
C.-P. Li, University of California - San Diego
I.V. Roshchin, University of California - San Diego
I.K. Schuller, University of California - San Diego
K. Liu, University of California - Davis
Correspondent: Click to Email
Deep sub-100 nm magnets have been the focus of intense research interest due to their fascinating fundamental properties and potential technological applications. Here we report the investigation of magnetization reversal in arrays of Fe nanodots prepared by a nanoporous alumina shadow mask technique.@footnote 1@ In particular we have examined the single domain to vortex state transition in 52, 58, and 67 nm nanodots, using a first order reversal curve (FORC) method.@footnote 2-5@ Striking differences in the FORC diagrams have been observed, despite only subtle differences in their major hysteresis loops. The 52 nm nanodots exhibit single domain behavior. The extracted coercivity distribution agrees well with a simple theoretical calculation. The 67 nm dots have more complex FORC characteristics which clearly indicate reversal via a vortex state. These experimental FORC features have been confirmed by OOMMF micromagnetic simulations. The 58 nm dots show characteristics common to both the 52 and 67 nm samples. By selectively integrating the normalized FORC distribution corresponding to the single domain phase, we have determined that 43% and 10% of the nanodots in the 58 and 67 nm sample, respectively, are in the single domain state. Additionally, we have studied the single domain phase fraction as a function of temperature in the 67 nm dots. With decreasing temperature, it is more difficult to nucleate vortices within the dots and the single domain phase fraction increases. @FootnoteText@ *Supported by NSF, ACS-PRF, AFOSR, UC-CLE, and the Alfred P. Sloan Foundation. @footnote 1@K. Liu, et al, Appl. Phys. Lett. 81, 4434 (2002). @footnote 2@C. P. Pike, et al, J. Appl. Phys. 85, 6660 (1999). @footnote 3@H. G. Katzgraber, et al. Phys. Rev. Lett. 89, 257202 (2002). @footnote 4@J. E. Davies, et al, Phys. Rev. B 70, 224434 (2004). @footnote 5@J. E. Davies, et al, Appl. Phys. Lett. 86, 262503 (2005).