Structural and Magnetic Properties of Granular Co-ZrO 2 Films
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Structural and Magnetic Properties of Granular Co-ZrO2 Films Z Konstantinović, M García del Muro, B J Hattink, M Varela1, X Batlle, and A Labarta Departament de Física Fonamental, Universitat de Barcelona, Avinguda Diagonal 647, 08028-Barcelona, Spain 1 Departament de Física Aplicada i Òptica, Universitat de Barcelona, Avinguda Diagonal 647, 08028-Barcelona, Spain ABSTRACT We present here the growth of Co-ZrO2 granular films by pulsed laser deposition (PLD). CoZrO2 prepared with PLD is an ideal system for investigating the properties of magnetic nanoparticle since the Co-ZrO2 interfaces are of high quality with no evidence of intermixing. The average composition of the samples is determined by x-ray photoemission spectroscopy and microprobe exsperiments. High resolution scanning electron microscopy shows existence of a regular distribution of Co nanoparticles embedded in the amorphous ZrO2 matrix. Ferromagnetic correlations among the Co nanoparticules are evident in the field-cooled state. The mean particle size and width of the distribution are determined by fitting the low-field magnetic susceptibility and isothermal magnetization in the paramagnetic regime to a distribution of Langevin functions. Magnetoresistance confirms its origin from the particle magnetization and also validates information about the particle distribution.
INTRODUCTION The rapid development of several thin film preparation techniques provides magnetic granular systems with a very well controlled nanostructure and thus, promising technological applications depending on basic properties of magnetic nanoparticles [1,2].From a scientific point of view, these technological advances make possible to prepare model of granular solids with well-controlled particle size and shape, thereby facilitating interpretation of their properties. Nevertheless, the behavior of these materials is determined by a complex interplay of intrinsic properties, size distribution of the nanoparticles, finite-size and surface effects and many body effects associated with interparticle interactions [3, 4, 5, 6]. In particular, granular films composed of Co clusters embedded in various insulating matrix is a very active research topic, where the interplay between the structure and magnetism can be studied [7, 8, 9, 10, 11]. In this paper, we present typical results of the magnetic and magnetotransport properties of granular Co-ZrO2 thin films prepared by pulsed laser deposition (PLD) with Co volume concentration x=0.42. Scanning electron microscopy shows a regular distribution of nanoparticles embedded in amorphous zirconia. Agglomerations of the Co particles in chains giving rise to a labyrinth structure manifest the proximity to percolation. The size distribution of magnetic nanoparticles is deduced from magnetic measurements. Although ferromagnetic interactions are evidenced from field-cooled (FC) measurements, the fitting of magnetoresistance using Julliere model by using a distribution of Langevin functions is still acceptable and gives rise to reasonable par
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