%0 Journal Article
%T Structural and Magnetic Properties of Microwave Assisted Sol-Gel Synthesized Manganite Nanoparticles
%A Mahin Eshraghi
%A Parviz Kameli
%J ISRN Nanotechnology
%D 2014
%R 10.1155/2014/867139
%X The structural and magnetic properties of nanoparticles of (LSMO) were studied using powder X-ray diffraction (XRD), transmission electron microscope (TEM), and magnetic measurements. The XRD refinement result indicates that samples crystallize in the rhombohedral structure with R-3C space group. The dc magnetization measurements revealed that samples exhibit no hysteretic behavior at room temperature, symptomatic of the superparamagnetic (SPM) behavior. The results of ac magnetic susceptibility measurements show that the susceptibility data are not in accordance with the N¨¦el-Brown model for SPM relaxation but fit well with conventional critical slowing down model which indicates that the dipole-dipole interactions are strong enough to cause superspin-glass-like phase in LSMO samples. 1. Introduction Magnetic nanoparticles are currently the subject of intense research because of their potential applications in high density magnetic storage and biomedical applications [1¨C3]. The perovskite manganite with the formula ( , Ca, Ba, or vacancies) has attracted considerable attention due to the discovery of the phenomenon of colossal magnetoresistance (CMR) and its potential application [4¨C7]. The properties of these materials are explained by double exchange theory of Zener [7] and electron lattice interaction [8]. By varying the composition and consequently tuning the ratio, the compound reveals various electronic, magnetic, and structural phase transitions at different temperatures. These phase transitions have been attributed to strong coupling among spin, charge, orbital degree of freedom, and lattice vibrations. It is well known that the magnetic and transport properties of these materials strongly depend on the particle size, due to the influence of structural and magnetic disorders at the grain boundaries [9¨C13]. The size effects and the large surface area of magnetic nanoparticles intensely change some of the magnetic properties compared to bulk counter parts. Manganite nanoparticles display features like lower values of magnetization [14], higher values of low field magnetoresistance [15], exhibiting superparamagnetic (SPM) phenomena [16], and so forth. SPM nanoparticles with single domain microstructure have a high potential as carriers for biomedical applications. According to the Stoner-Wohlfarth theory, the magnetocrystalline anisotropy energy, , of a single-domain particle can be approximated by , where is the magnetocrystalline anisotropy constant, is the volume of the nanoparticle, and is the angle between the magnetization direction and the
%U http://www.hindawi.com/journals/isrn.nanotechnology/2014/867139/