Effect of Diamagnetic A 2+ Substitution on the Magnetic and Ferroelectric Properties of the Bi 1-x A x FeO 3 Multiferroi
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Effect of Diamagnetic A2+ Substitution on the Magnetic and Ferroelectric Properties of the Bi1-xAxFeO3 Multiferroics V. A. Khomchenko1, D. A. Kiselev1, J. M. Vieira1, Li Jian1, A. M. L. Lopes2, Y. G. Pogorelov2, J. P. Araujo2, and A. L. Kholkin1 1 Department of Ceramics and Glass Engineering & CICECO, University of Aveiro, Aveiro, 3810-193, Portugal 2 IFIMUP/ Department of Physics, University of Porto, Rua Campo Alegre 687, Porto, 4169-007, Portugal ABSTRACT Investigation of crystal structure, magnetic and local ferroelectric properties of the diamagnetically-substituted Bi1-xAxFeO3 (A= Ca, Sr, Pb, Ba; x= 0.2, 0.3) ceramic samples has been carried out. It has been shown that the solid solutions have a rhombohedrally distorted perovskite structure described by the space group R3c. Piezoresponse force microscopy data have revealed existence of the spontaneous ferroelectric polarization in the samples at room temperature. Magnetization measurements have shown that magnetic state of these compounds is determined by the ionic radius of the substituting elements. A-site substitution with the biggest ionic radius ions has been found to suppress the spiral spin structure of BiFeO3 and to result in the appearance of weak ferromagnetism. The magnetic properties have been discussed in terms of the substitution- induced changes of the magnetic anisotropy. INTRODUCTION Multiferroics which exhibit a coupling between magnetic and ferroelectric order parameters have been widely noted as materials promising for applications in multiple-state memory devices. However, a sufficiently strong coupling of the order parameters has not been obtained at room temperature so far. Known magnetic ferroelectrics tend to have low magnetic ordering temperature and are often antiferromagnets, in which a sizable response to the application of magnetic field cannot be expected. Among all known multiferroics, BiFeO3 is one of the most promising material for the technological applications, since spin and dipole orderings in the compound coexist at room temperature (the Neel temperature is about 640 K, the ferroelectric Curie temperature is about 1100 K). However, it is an antiferromagnet with a spatially modulated spin structure [1], which does not allow net magnetization and also inhibits observation of the linear magnetoelectric effect [2]. One of the possible ways of inducing net magnetization in BiFeO3 is a chemical substitution in the A-sublattice of the ABO3 perovskite. The substitution is able to suppress the incommensurate spin structure [3] and to cause the spontaneous magnetization through antisymmetric exchange mechanism [4-6]. Enhancement of magnetization has been reported both for the Bi1−xRExFeO3 (RE = Nd, Sm, Tb etc.) solid solutions doped by magnetically active rare-earth ions [7-9] and for the diamagnetically- substituted Bi1−xAxFeO3 (A= La, Ba, Pb) samples [10- 12]. It has been found that value of the net magnetization depends strongly on the kind of the diamagnetic substituting element [12]. While the existence of this de
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