Eur. Phys. J. B (2013) 86: 410
https://doi.org/10.1140/epjb/e2013-40353-3

Regular Article

Magnetic ordering of spin systems having fractal dimensions Experimental study^*

¹ Graduate School of Science and Engineering, Ehime University, 2-5, Bunkyo-cho, Matsuyama, 790-8577 Ehime, Japan
² Research Institute for Electronic Science, Hokkaido University, Kita 21, Nishi 10, Sapporo, 001-0021 Hokkaido, Japan
³ Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Naka, 319-1195 Ibaraki, Japan

^a e-mail: tnaito@ehime-u.ac.jp
^b Present address: Department of Chemistry, Asahikawa Medical University, Asahikawa, 078-8510 Hokkaido, Japan
^c Present address: College of Engineering, Ibaraki University, 4-12-1 Nakanarisawa-cho, Hitachi, 316-8511 Ibaraki, Japan

Received: 13 April 2013
Received in final form: 19 June 2013
Published online: 2 October 2013

Abstract

It is well-known that cooperative properties such as magnetic ordering can depend on the samples’ dimensions (Ds) in a qualitative way. However, there have been no samples with well-defined non-integer Ds. The dimension of a given sample has been always discussed on the anisotropy of the electronic/crystal/magnetic structures, which has no definition suitable for quantitative discussion on dimensions vs. properties. On the other hand a particular type of porous samples, i.e. fractal bodies, can have well-defined non-integer Ds dependent exclusively on the geometrical feature of structures, and physical properties of such materials remains unexplored. This paper reports on magnetic ordering in samples covering 2.5 ≤ D ≤ 3, in addition to a way of precise control of the fractal dimensions of given samples simply by wax (alkylketene dimer). The results show that the magnetic ordering temperatures, i.e. Néel temperatures (T_Ns), of CoO depend on D, and rapidly enhance immediately below D = 3. This means that one can control or enhance the critical temperature simply by tuning D with keeping the remaining magnetic properties unchanged.