Magnetic and magnetotransport behavior of granular Fe x Ag 100x thin films G. Sarmiento a, * , M.L. Fdez-Gubieda a , I. Orue b a Dpto. Electricicidad y Electro ´ nica, Universidad del Paı ´s Vasco (UPV/EHU), Apdo. 644, 48080 Bilbao, Spain b Servicios Generales de Investigacio ´ n (SGIKER), Vicerrectorado de Investigacio ´ n, UPV/EHU, Spain Available online 15 February 2007 Abstract We present magnetic and magnetotransport properties of Fe x Ag 100x granular thin films prepared by the pulsed laser deposition tech- nique. Increasing the Fe nanoparticles, x, the interactions among them modify the magnetic response from an interacting superparamag- netism to a ferromagnetic-like behavior with a crossover at x = 25. For this value, an extraordinary Hall effect becomes dominant while magnetoresistance decrease. The appearance of in-plane anisotropies are discussed through the study of extraordinary Hall effect. Ó 2007 Elsevier B.V. All rights reserved. PACS: 75.75.+a; 73.63.b Keywords: Laser deposition; Magnetic properties; Nanoparticles, colloids and quantum structures; Nanoparticles 1. Introduction Magnetic nanostructrures present outstanding proper- ties, such as giant magnetoresistance, GMR [1,2] and novel magnetic properties due to nanoscale [3]. While isolated noninteracting nanoparticles present ideal superparamag- netism, SP; increasing the amount of magnetic nanoparti- cles, the competition between interparticle interactions mainly of dipolar and exchange character and the intrapar- ticle anisotropy energy [3] give rise to different magnetic regimes. Below the percolation threshold, we find, interact- ing superparamagnetism, ISP [4], and for higher concentra- tion correlated super spin glass [3] and superferromagnetism [5] behaviors are described. The influence of magnetic inter- actions in MR has also been reported [6–8]. Another inter- esting magnetotransport tool is the Hall effect, because the correlation between the Hall signal and magnetization is well established [9,10]. In this work we have studied the influence of the Fe con- tent in the magnetic and magnetotransport properties of Fe x Ag 100x (x = 6, 15, 25, 31, 49 atomic percentage) granu- lar thin films. 2. Experimental The films were prepared by the pulsed laser deposition technique using a Lambda Physik Compex 102 Laser (k = 248 nm, 100 mJ per pulse) onto single crystal Si h100i substrate, at room temperature and 2 · 10 5 mbar in a depo- sition chamber. The target is a rotating disc divided into sectors of Fe and Ag whose areas are chosen to get the desired final composition. The frequency of the laser pulse was 15 Hz and the target was rotating at angular speed of 30 rpm. The film thickness, ranging from 80 to 150 nm, was determined by Atomic Force Microscopy. The compo- sitional analysis had been done by means of Rutherford Backscattering and Energy Dispersion analysis. Magnetiza- tion loops were performed in a 7 T SQUID magnetometer at 5 K and 300 K. The magnetoresistance, defined as, MR% = 100 · [R(l 0 H)  R(l 0 H = 0)]/[R(l 0 H = 0)] was 0022-3093/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2006.12.078 * Corresponding author. Tel.: +34 946015371; fax: +34 946013071. E-mail address: websamug@lg.ehu.es (G. Sarmiento). www.elsevier.com/locate/jnoncrysol Journal of Non-Crystalline Solids 353 (2007) 944–946