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Theoretical and experimental study of multiferroics BiFeO3 and Bi(1-x)HoxFeO3

Among the different types of multiferroic compounds, bismuth ferrite (BiFeO3 ; BFO) stands out because it is perhaps the only one being simultaneously magnetic and strongly ferroelectric at room temperature. BiFeO3 and Bi1-xHoxFeO3 ultrafine nanopowders were synthesized by the hydrothermal method. Here we use simple, low-cost and energy-saving hydrothermal method, which has advantages over the conventional methods. The influence of Ho doping on the crystal structure and magnetic properties of bismuth ferrite (BFO) nanopowders was investigated. The diffraction pattern was recorded at room temperature and atmospheric pressure in the absence of any re-heating of the sample. A fitting refinement procedure using the Rietveld method was performed which showed the incorporation of Ho3+ ions in the BiFeO3 crystal lattice, where they substitute Bi3+ ions. All the samples belong to R3c space group.In addition, theoretical investigation using bond valence calculations have been performed in order to mimic pure and Ho doped BiFeO3 compounds produced in the experiment. Various BFO polymorphs were investigated as function of holmium concentration and final optimization of crystal structures has been performed on ab initio level using Density Functional Theory (DFT). Furthermore, electronic and magnetic properties of BiFeO3 were investigated using combination of experimental and theoretical methods.Magnetic behavior of synthesized materials was investigated by SQUID magnetometer in wide temperature interval (2-800 K). Splitting between the zero-field-cooled and field-cooled magnetization curves becomes more pronounced as the Ho concentration is increased, pointing to the development of weak ferromagnetic moment, which is usually connected with uncompensated spins or spin canting. Hysteresis loops show the same fact, attaining higher magnetization with more Ho included, and becoming wider, i.e. magnetically harder. Acknowledgmant: The authors acknowledge the financial support of Croatian Science Foundation (project Multiferroic and Magnetoelectric Systems - FerMaEl UIP-2014-09-8276)

Bismuth ferrite ; Multiferoics ; Magnetoelectric effect

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