Surface spin-glass, large surface anisotropy, and depression of magnetocaloric effect in La0.8Ca0.2MnO3 nanoparticles

Abstract

The surface magnetic behavior of La 0.8 Ca 0.2 MnO 3 nanoparticles was investigated. We observed irreversibility in high magnetic field. The surface spin-glass behavior as well as the high-field irreversibility is suppressed by increasing particle size while the freezing temperature T F does not change with particle size. The enhanced coercivity has been observed in the particles and we attributed it to the large surface anisotropy. We have disclosed a clear relationship between the particle size, the thickness of the shell, and the saturation magnetization of the particles. The large reduction of the saturation magnetization of the samples is found to be induced by the increase of nonmagnetic surface large since the thickness of the spin-disordered surface layer increases with a decrease in the particle size. Due to the reduction of the magnetization, the magnetocaloric effect (MCE) has been reduced by the decreased particle size since the nonmagnetic surface contributes little to the MCE. Based on the core-shell structure, large relative cooling powers RCP(s) of 180 J/kg and 471 J/kg were predicted for a field change of 2.0 T and 4.5 T, respectively, in the small particles with thin spin-glass layer. V C 2012 American Institute of Physics. [http://dx

Chemical, electronic, and magnetic structure of LaFeCoSi alloy: Surface and bulk properties

“…8 For example, in materials such as manganites, the changes of magnetic and, in particular, magnetocaloric properties, have been investigated as a function of particle size, resulting, often, in a reduction of the MCE for smaller particles, where the reduction has been ascribed to the presence of a surface layer with properties different from the bulk. [9][10][11] On the other hand, a careful control of the thickness and the magnetic properties of this surface layer has been proposed in order to obtain a larger relative cooling power for nanoparticles when compared with the corresponding bulk material. 11 Within this scenario, it appears important a detailed characterization of the surface of magnetocaloric materials that, incidentally, is a largely unexplored research field.…”

“…[9][10][11] On the other hand, a careful control of the thickness and the magnetic properties of this surface layer has been proposed in order to obtain a larger relative cooling power for nanoparticles when compared with the corresponding bulk material. 11 Within this scenario, it appears important a detailed characterization of the surface of magnetocaloric materials that, incidentally, is a largely unexplored research field. This is partially due to the production methods typically employed for magnetocaloric systems that lead to a relatively weak control of the surface properties.…”

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“…For LSMO the magnetization, as a function of magnetic field, presents a hysteresis behavior for the NP while the bulk samples are free of magnetic losses . Xi et al concluded that it is due to the large surface anisotropy. Therefore, we assume that the magnetic anisotropy constant of the surface is larger than the bulk one, i.e.…”