Structural, microstructural and magnetic investigations in high-energy ball milled BiFeO₃ and Bi_0.95Eu_0.05FeO₃ powders

Abstract

In this paper, synthesis, structural, microstructural and magnetic properties of high-energy ball milled BiFeO₃ and Bi_0.95Eu_0.05FeO₃ powders were thoroughly investigated through X-ray diffraction, scanning electron microscopy, Mössbauer spectroscopy and magnetization measurements. Single-phased compounds were processed by using both mechanosynthesis and post-milling annealing. The set of results did not indicate considerable alterations in the magnetic ordering of the powders, even though their ordering temperature, magnetization and coercivity were highly sensitive to the narrow grain sizes distribution of nanograins and substituting Eu ion. In addition, we have shown that enhanced magnetic properties of BiFeO₃ could be achieved by a low degree of Eu substitution, yet preserving the structural and microstructural characteristics of the processed powders.

Introduction

In recent years, many techniques have been employed to process single-phase magnetoelectric oxide materials [1], [2]. Among them, the high-energy ball milling (HEBM) technique has emerged as an attractive alternative [3]. High-energy ball milled products usually show high defect density, large surface area and enhanced diffusion rates [4]. This is due to the introduction of an excess of energy into the crystal lattice during the milling process, where the start materials are submitted to fracturing, deformation and welding [4], [5], facilitating the precursor reaction and, consequently, the final phase formation [4]. In particular, the suitability of HEBM for processing the BiFeO₃ multiferroic magnetoelectric compound, which has attracted much academic and technological attention [5], [6] as a promising candidate for applications in spintronics [7], [8] was recently demonstrated [9], [10].

Cationic substitutions in the structure of the BiFeO₃ magnetoelectric compound have been indicated as an attractive procedure for tuning its magnetic and electrical properties, as well as its magnetoelectric coupling intensity [9], [11]. The advantages of being able to tune the electrical and magnetic properties of the BiFeO₃ and BiEuO₃ compounds, make efforts at synthesizing these materials, especially in nanoscale, imperative [9], [10], [11], [12]. In this paper, the structural, microstructural, magnetic, and Mössbauer spectral properties of the BiFeO₃ and Bi_0.95Eu_0.05FeO₃ multiferroic magnetoelectric compounds, synthesized by the high-energy ball milling technique, were studied through X-ray diffractometry, scanning electron microscopy, magnetometry and Mössbauer spectroscopy. As it will be shown, the Eu substitution in BiFeO₃ structure can probably breaks its cycloidal spin structure, enhancing the coercivity of processed powders.