The recent progress made in lithography technologies allows the elaboration of well-controlled artificial structures exhibiting exciting behaviors such as quantum magnetism, order - disorder statistics... This is also the case for magnetic nanostructures for which the elaboration artificial networks of ferromagnetic single-domain structures allows to explore local magnetism, and in particular magnetic interactions between artificial nanostructures.

In a geometrically ordered network[1], these interactions generate magnetic frustrations similar to those observed in Spin-Ice systems[2]. The size and shape of the nanostructures are chosen so that only the single-domain configuration is stable (a few tens of nanometers and strong shape anisotropy) in order to avoid any influence of micromagnetism. The system can then be modeled by a network of spins (magnetic single-domain) arranged in the form of networks treated within the Ising model approximation[3]. Using lithography techniques, we can then create but also control the problem of magnetic frustration.

We present the results of a first study of frustrated magnetic systems composed of hexagonal (Kagomé) and square ordered networks using the combination of high-resolution X-PEEM microscopy and Magnetic Force microscopy. The goal of this work is to highlight the importance and the influence of short-range interactions and of the geometry on the magnetic frustration phenomena and relaxation.

Figure : ‘Spin-Ice’ Kagomé Network : periode 700nm. Nanostructure individual size : 100x400nm. a) LEEM microscopy image b) Magnetic domains images obtained using X-PEEM microscopy highlighting the magnetic frustration.

[1] Moessner, R. Can. J. Phys. 79, 1283-1294 (2001).

[2] R. F. Wang, C. Nisoli, R. S. Freitas, J. Li, W. McConville, B. J. Cooley, M. S. Lund, N. Samarth, C. Leighton,V. H. Crespi et P. Schiffer Nature 439, 303 (2006)

[3] M. Tanaka, E. Saitoh, H. Miyajima, T. Yamaoka et Y. Iye. Phys Rev B 73, 052411 (2006).

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