Multiferroic materials are of great interest from the scientific and technological viewpoints based on their multifunctional behavior involving ferroelectricity, ferromagnetism, ferroelasticity and strong electromagnetic coupling properties. Among these materials, BiFeO3 (BFO), is a well-known multiferroic with simultaneous ferroelectricity (TC=1103K) and G-type antiferromagnetism (TN=643K). In this work, we doped BiFeO3 with Mn species and studied the doping effect on the corresponding magnetic properties, expected from the substitution of Bi3+ by Mn2+. Additionally, the optimum processing conditions to minimize the formation of any impurity phase were also identified. X-Ray Diffraction (XRD) characterization confirmed the formation of powdered impurity-free BFO in pure and 7 at.% Mn-BFO only after annealing of the precursor compounds at suitable temperatures and time (700°C, 15 minutes). Scanning Electron Microscopy (SEM) analyses were used to determine the size and morphology of synthetized powders. Vibrating sample magnetometry (VSM) measurements showed that maximum magnetization values increased with doping and reached a maximum value in the 7 at.% Mn-doped BFO annealed at 700°C for 15min; the corresponding magnetization in the non-saturated MH loops reached 0.68 emu/g. This behavior can be attributed to the actual incorporation of Mn species into the BFO lattice and the substitution of non-magnetic Bi species.

The present work addresses the systematic evaluation of the influence of the incorporation of dopant species (Ca+2, Ag+1) on the structural and functional properties of bismuth ferrite (BFO) nanocrystalline powders and films. Pure and doped BFO powders and thin films were synthesized by a modified sol-gel method. The concentration of the doping species varied from 0 up to 7 at %. The development of the host BFO structure was confirmed by XRD analyses of samples annealed at 700°C for one hour in air and nitrogen atmosphere. Thicknesses of films varied between 80 and 200 nm, depending on the concentration of Ca+2 species. Doped BFO exhibited a magnetic behavior that turned from paramagnetic into ferrimagnetic with the increase of Ca+2 concentrations.

The effective incorporation of dopant species into ZnO host structure should induce changes in its physical and chemical properties enabling the establishment of novel multi-functional properties. Doping with transition metal ions and the subsequent exchange interaction between available spins of the magnetic species are expected to induce a ferromagnetic behavior. This ferromagnetic functionality will enable the application of this material in data storage and spintronics-based devices. The present research addresses the study of the effect of the oxidationstate of Fe species and the influence of the annealing atmosphere on the structural and functional properties of nanocrystalline ZnO-based powders.

The present study addressed the effect of the incorporation of Praseodymium species in the BiFeO3(BFO) structure on the corresponding structural and functional properties of powders and films. The level of the doping species varied from 0 at% to 4 at%. BFO powders and thin films were synthesized by a sol-gel method, where glycol was aggregated to the main solvent to increase the viscosity of the precursor solutions and promote their adhesion onto platinum substrates. The development of the host BFO structure was confirmed by XRD analyses of samples annealed at 700°C for one hour (powders) or 500°C for 2 hours (thin films), in air. The average crystallite size varied from 37 nm to 41 nm and 28nm to 40nm for powders and thin films, respectively, due to the increase of the doping level. The incorporation of specific dopant species played an important role in the ferromagnetic and ferroelectric behavior in the material.

The main challenge associated with the synthesis of pure bismuth ferrite (BFO) is the extremely high stability of parasitic or secondary phase Bi-oxides, which contaminates the single ferrite phase and affects the corresponding functional properties. Therefore, any attempt to determine the optimum synthesis conditions conducive to the inhibition of the formation of those impurity phases becomes indispensable. Accordingly, the present work addresses the systematic evaluation of the type of solvent and synthesis parameters to exclusively produce the BFO structure. Nanocrystalline BFO powders were synthesized after thermal treatment of the solid intermediates formed in ethylene glycol and acetic acid media. The experimental work also considered the effect of the excess of Bi species with respect to the BiFeO3stoichiometry and the annealing of the intermediates at different temperatures. The structure formation was confirmed by XRD analysis and magnetic properties were studied by VSM. X-ray diffraction analyses confirmed that powders exhibiting single phase BFO structure were produced after annealing the intermediate which was formed in acetic acid for one hour at 700°C. The average crystallite size and lattice parameter were calculated to be approximately 40 nm and 5.36 Å, respectively. It was also found that the synthesis under 7% of Bi-stoichiometric excess inhibited the formation of the parasitic phases after annealing the intermediate produced in ethylene glycol medium. The saturation magnetization of the powders annealed at 700°C were 0.15 emu/g and 0.17 emu/g when the BFO intermediates were formed in ethylene glycol and acetic acid media, respectively. The corresponding coercivity values were 6 Oe and 21 Oe.

A systematic study was carried out to determine the effect of the composition and annealing atmosphere (air and N2) on the structural, optical and magnetic properties of pure, doped and co-doped ZnO [Zn(1-y)(CoV)yO] nanocrystalline powders and films. The (Co+V) doping level, ‘y’, was fixed at 2 at% with variable individual concentrations of Co and V species. Powders and films were synthesized via a sol-gel approach where the films were grown on silicon (100) substrates. X-ray diffractometry verified the formation of the ZnO host structure after annealing of the precursor phases. The variation of the average crystallite size of Co-V (2 at.%) ZnO powders annealed in air at 500°C were negligible and averaged 33 nm. Photoluminescence (PL) measurements of powder corroborated the formation of high-quality ZnO host structure, as well as in films annealed in air. In turn, XRD and PL measurements confirmed an enhanced crystallinity of the ZnO host, with an average crystallite size of 41 nm, for films annealed at 500°C under a N2 atmosphere. M-H measurements evidenced a ferromagnetic behavior at room temperature in powders and films that was dependent on the type and amount of the dopant species.

This study reports on the structural and magnetic characterizations of free-standing bismuth ferrite, BiFeO3, nanoparticles synthesized in polyol medium. Fine tuning of the ferrite magnetic properties was achieved by adding an excess bismuth species or doping with cobalt ions, coupled with thermal annealing. Crystalline Bi1-yCoyFeO3 powders (where ‘y’ ranges from 0.00 to 0.10) were produced after annealing the precursors for one hour at 700οC. The average crystallite size was calculated to be approximately 22 nm. We found that the synthesis under stoichiometric excess of Bi species (up to 10 at.%) promoted a more complete crystallization of the material, i.e., no precursor phases remained. Furthermore, both the saturation magnetization and the coercivity of the synthesized powders were strongly influenced by the concentration of Co. They increased from 0.13 emu/g and 19 Oe to 3.5 emu/g and 1183 Oe for pure BiFeO3 and 10 at.% Co-doped BiFeO3, respectively.