S.N. de Medeiros

Structural, Magnetic, and Dielectric Investigations of the FeAlO3 Multiferroic Ceramics

The FeAlO3 phase presents an orthorhombic symmetry (Pna21 space group) with a double combination of hexagonal and cubic closed packing of oxygen ions. In this phase, there are four distorted different cationic sites, promoting piezoelectricity, ferrimagnetism and magnetoelectric effects at low temperatures. In this work, high-energy ball milling was employed to produce the FeAlO3 multiferroic compound. Its structural (Rietveld refinement), dielectric and magnetic properties were carefully investigated.

Structural, Microstructural and Magnetic Properties of the High-Energy Ball Milled BiFeO3 and BiFe0.95 Mn0.05O3 Ferroelectromagnetic Compounds

Multiferroic BiFeO3 ceramic powders were synthesized through high-energy ball milling. The structural, microstructural and magnetic properties of the obtained samples were carefully determined. The obtained samples were very fractured and strained due to the employed milling conditions, motivating the agglomeration of the nanopowders. The unit cell, Mössbauer and magnetic parameters presented considerable alterations in comparison with those for bulk materials, as a consequence of mechanosynthesis. The modification of BiFeO3 with 5 mol% of Mn ions do not induces significant microstructural or structural alterations in as-milled or annealed samples. However, an intense magnetization decreasing was observed.

Structural and Mössbauer characterization of the ball-milledFex(Al2O3)100−x system

Metal-oxide composites were synthesized by high-energy ball milling of metallic iron (α-Fe) and alumina (α-Al2O3) powders, varying the starting relative concentration and the milling time. The samples were characterized by scanning electron microscopy, x-ray diffraction, and Mossbauer spectroscopy. The results revealed the formation of a FeAl2O3+W spinel phase (hercynite) and of iron (super)paramagnetic nanoprecipitates, in addition to residual magnetic iron and alumina. We also observed that the relative amounts of nanoprecipitates and hercynite for isochronally milled samples were correlated with the sample nominal concentration x, with the precursor iron being relatively more converted in those phases for low x values. Particularly for x=10 milled sample, the relative amounts of the (super)paramagnetic and spinel phases were observed to increase linearly with the milling time. An x=20∕24h milled sample was annealed in H2 atmosphere and revealed the reduction of hercynite, with iron phase separation.