Journal of Magnetism and Magnetic Materials 258–259 (2003) 119–124 Electronic noise in magnetic low-dimensional materials and nanostructures B. Raquet a, *, M. Viret b , M. Costes a , M. Baibich c , M. Pannetier b , M. Blanco- Mantecon b , H. Rakoto a , A. Maignan d , S. Lambert d , C. Fermon b a Laboratoire National des Champs Magn ! etiques Puls ! es, LNCMP, Av. de Rangueil, 31432 Toulouse, France b CEA, Saclay, Service de l’Etat Condens ! e, Orme des merisiers, 91191 Gif sur Yvette, France c Instituto de F! ısica, UFRGS, Av. Bento Gon , calves 9500, Caixa Postal 15051, 91501-970 Porto Alegre, RS Brazil d Laboratoire CRISMAT, UMR CNRS 6508, ISMRA, Boulevard du Mal Juin, 14050 Caen, France Abstract After a brief review underlining the power of electronic noise studies to probe local magnetic instabilities, we present new data in three different systems in terms of dimensionality and magnetic ordering: the first results we present deal with low-frequency longitudinal and Hall resistance fluctuations in Ni nanostructures, where we address the questions of the inhomogeneous behavior of the noise at a nanometric scale. In order to get some insight into the atomic process, wereportonnoisegeneratedinatomiccontactsofNiobtainedbythebreakjunctiontechnique.Andfinally,wepresent the first electronic noise study in a one-dimensional frustrated magnetic Ca 3 Co 2 O 6 single crystal composed of parallel Co spin chains. From the magnetic noise analysis, we discuss the interplay between the low-temperature three- dimensional magnetic ordering and the spin-dependent hopping conductivity on the Co sites. r 2002 Elsevier Science B.V. All rights reserved. Keywords: Electronic noise; Magnetic fluctuations; Magnetic nanoctructures; Low-dimensional magnetic oxides; Ca 3 Co 2 O 6 single crystal With the advent of information technologies and their drive to reduce devices size, there is presently a renewed interest in studying mesoscopic magnetic structures and low-dimensional magnetic materials, especially regard- ing noise properties. Noise of magnetic origin, called ‘‘mag-noise’’, represents a most interesting physical quantity to probe the intrinsic electronic and magnetic properties of low-dimensional materials and devices. The phenomena involved in generating the noise include thermal spin fluctuations, magnetic domains instabilities (magnetization orientation fluctuations), vibrational excitations of magnetic domain walls or domain wall hopping between pinning sites. These distinct sources of noise, called ‘‘fluctuators’’, explain why magnetic fluctuations can cover more than 12 decades in the frequency space from the mHz to few GHz. We may distinguish two kinds of mag-noise investigations : the first one is based on direct measurements of the magnetic activity dMðtÞ [1–3]. Very recently, using a scanning niobium micro-squid microscope, the magnetic fluctuations of self-assembled cobalt nanoparticules arising from thermally activated nanoparticle spin flips have been measured [3]. The second type of mag-noise studies relies on electronic noise measurements on conducting magnetic materials, exploring the galvano- magnetic coupling between magnetic instabilities and the spin-dependent charge carriers scattering [4,5].Ithas been demonstrated that non-Gaussian resistivity fluc- tuations dRðtÞ; far above the electronic apparatus noise, may be an unique fingerprint of localized magnetic fluctuationsoftheorderoffewhundredsof m B [6,7].The electronic noise studies on magnetic materials also give an insight into the electronic transport properties and constitute a powerful probe of microscopic mechanisms which drive electronic and magnetic transitions. *Corresponding author. Lab. de Physique de la Matiere, Condensee de Toulouse, Av. de Ragueil, Toulouse 31077, France.. E-mail address: raquet@insa-tlse.fr (B. Raquet). 0304-8853/03/$-see front matter r 2002 Elsevier Science B.V. All rights reserved. PII:S0304-8853(02)00993-9