Magnetic and structural investigations on La0.6Sr0.4MnO3 nanostructured manganite: Evidence of a ferrimagnetic shell

• Evidences of ferromagnetic shell in La0.6Sr0.4MnO3 ferromagnetic nanoparticles.
• Core(ferromagnetic)–shell(ferromagnetic) model for nanostructured manganite.
• Sol–gel method was successfully used to obtain nanostructured manganite.

This paper presents the structural and magnetic properties of La0.6Sr0.4MnO3 nanoparticles with sizes from 21 to 106 nm, which have been prepared using the sol–gel method. The reduction of the nanoparticles׳ size tends to broaden the paramagnetic to ferromagnetic transition, as well as to promote magnetic hysteresis and a remarkable change on the magnetic saturation. In order to better understand the magnetic behavior of those nanoparticles, a simple model based on a ferromagnetic core and a ferrimagnetic shell was considered, where the magnetization was described in terms of the standard mean-field Brillouin function. This model matches the experimental data, leading to conclusion the nanoparticles with size <40nm are single magnetic domain. In addition, the output fitting parameters give information on the Landé factor of the core and shell.

Core–shell model: The core has a ferromagnetic character, while the shell is ferrimagnetic. Each one has two sub-lattices (Mn3+ and Mn4+) that interact through a mean-field (see Eq. (6)). Interactions strength and signals are also represented in this figure. In this figure the arrows (or vectors) represent the magnetic moment of ions Mn3+ (s=2) and Mn4+ (s  =3/2). βλβλ׳s describe the ferromagnetic interaction between Mn4+ ions into the core (βλco) and into the shell (βλsh), while αλαλ׳s represent ferromagnetic interaction between Mn3+ ions into the core (αλco) and into the shell (αλsh). The −λsh−λsh and +λcoco+λcoco are associated to the mean field parameter of interaction between Mn3+ and Mn4+ sub-lattices in the shell (ferrimagnetic, negative sign) and core (ferromagnetic, positive sign), respectively.Figure optionsDownload as PowerPoint slide