Synthesis And Properties Of Magnetic Nanoparticles With Tunable Magnetic Anisotropy Energy
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Synthesis And Properties Of Magnetic Nanoparticles With Tunable Magnetic Anisotropy Energy Vincent Dupuis, Véronica Gavrilov-Isaac, Sophie Neveu, Merwen Aouadi, Sébastien Abramson Sorbonne Universités, UPMC Univ Paris 06, UMR 8234, PHENIX, F-75005 Paris, France CNRS, UMR 8234, PHENIX, F-75005 Paris, France, ABSTRACT In this paper, we discuss several strategies to tailor magnetic properties related to the magnetic anisotropy energy, such as the blocking temperature or the low temperature coercivity, of magnetic nanoparticles or materials made with magnetic nanoparticles. We describe a first approach that consists in synthesizing and dispersing bi and tri-magnetic core-shell nanoparticles that include a core made of a material with a weak anisotropy energy density and a shell made with a material with a large anisotropy energy density. This approach is a promising route to tune the blocking temperature of low temperature coercivity of a particle without altering its magnetization and with a good control of its size. Additionally, we also explore another route for the control of the shape of the hysteresis loop of material made with magnetic nanoparticles that consists in the simple mixture of magnetically soft and hard magnetic nanoparticles to create binary mixtures. In this case, it is the mixing ratio that allows one to adjust the properties of the final material. INTRODUCTION Magnetic single domain nanoparticles can be seen as the nanoscale analogue of permanent magnets and are found in an increasing variety of applications, ranging from engineering (i.e. smart nanocomposite materials that respond to an applied magnetic field) to nanomedicine (i.e. MRI, magnetic hyperthermia in cancer therapy or magnetically assisted drug delivery) [1,2]. Thanks to their huge magnetic moment µ, equal to the saturation magnetization ms times the volume of the particule Vp, they can be easily manipulated using the field gradients produced by inexpensive magnets [3]. Another important property of these particles, that proved to be crucial for an increasing number applications, is their magnetic anisotropy energy, that is the strength of the energy barrier that opposes the fluctuations of the orientation of the particle’s magnetic moment and makes it stick to its easy axis [4]. While weak anisotropy energies yield room temperature superparamagnetism with a reversible magnetization process, large anisotropy energies, easily obtained with Cobalt ferrite (Table 1), give the possibility to trap a remanent magnetization with significant coercivity at room temperature and thus create permanent nanocomposite magnets [5]. Among the various methods used in the last decades to prepare magnetic nanoparticles two have become very popular: co-precipitation [6,7,8] and thermal decomposition [9,10]. While the co-precipitation performed in alkaline conditions is a fast and cheap method to prepare large amounts of biocompatible magnetic nanoparticles (with however a significant size polydispersity), thermal decomposition of metallic precursor (done at
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