Vertical magnetization process in sub-micron permalloy dots

N. Kikuchi, S. Okamoto, O. Kitakami, Y. Shimada, S. G. Kim, Y. Otani, K. Fukamichi

Research output: Contribution to journalConference articlepeer-review

16 Citations (Scopus)


For a circular dot with the lateral size larger than the exchange length lex(= A1/2/M8), it is well known that the stable remanent state is a vortex structure where the spins around the center of the dot direct up-or down-ward. If only these two states are allowed in the vortex structure, it is possible to use it as a bi-stable memory element. In order to cheek this possibility, we have investigated vertical magnetization process of various sub-micron permalloy dots by PMOKE and MFM. Polycrystalline circular dots with 180-4000 nm in diameter and 40-80 nm in height were fabricated using electron. Lithography and a lift-off technique. While PMOKE measurements show very low remanence against vertical field, MFM detects distinct spin vortex structures where spins around the dot centers direct up-or down-ward. This result suggests a possibility of spin vortex structures as bi-stable switching memory elements, although their averaged remanence is quite small. From LLG calculations, it is found that lateral dimension of the spin vortex coincides with the exchange length lex = A1/2/M8, ∼ 15 nm regardless of the dot diameter. Furthermore we have established a magnetic phase diagram of permalloy dots as functions of dot diameter and height.

Original languageEnglish
Pages (from-to)2082-2084
Number of pages3
JournalIEEE Transactions on Magnetics
Issue number4 I
Publication statusPublished - 2001 Jul
Event8th Joint Magnetism and Magnetic Materials -International Magnetic Conference- (MMM-Intermag) - San Antonio, TX, United States
Duration: 2001 Jan 72001 Jan 11


  • Bi-stable memory
  • Exchange length
  • Lithography
  • Permalloy dot
  • Spin vortex


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