Dipolar and magnetic ordering in Nd-modified BiFeO3 nanoceramics

https://doi.org/10.1016/j.jmmm.2008.05.005Get rights and content

Abstract

The polycrystalline samples of Bi1−xNdxFeO3 (BNFO) with x=0, 0.05, 0.1, and 0.15 were prepared by a chemical route (metal ion complex precursor solution method). A systematic change in crystal structure from rhombohedral to tetragonal on increasing Nd substitution was observed. The reduction of low-frequency dispersion in permittivity and loss pattern due to Nd substitution in BiFeO3 (BFO) was observed in its dielectric response curve. The loss tangent (tan δ) was found to be reduced on increased Nd concentration in BNFO. Dielectric anomaly near the reported Neel temperature of BFO and peaks in all the BNFO samples were observed in the permittivity vs. temperature graph. Significant opening in the room temperature MH loop was observed on Nd substitution, which was more prominent for higher concentration of Nd.

Introduction

Simultaneous occurrence of electric and magnetic ordering in same phase has made multiferroic materials, a boon for the future technology in information storage and sensors [1], [2]. Though, nowadays, a good number of multiferroics of different structural family are available, BiFeO3 (BFO) with perovskite structure has been considered as one of the most fascinating multiferroic material because both of its ferroelectric transition (850 °C) [3] and antiferromagnetic Neel temperature (370 °C) are well above the room temperature [4]. Unfortunately, the formation of secondary phase during synthesis, low resistivity due to oxygen ion vacancy and spiral spin structure are some of the major problems of this material, for fabrication of multifunctional devices [5], [6], [7]. It has been observed that partial substitution of rare-earth elements like La or Nd at the Bi site of BFO helps in eliminating the secondary (pyrochlore) phase along with a structural phase transition improving ferroelectric properties and also helps in releasing latent magnetization locked within the spin cycloid [8], [9]. Though multiferroic properties of Nd-substituted BFO on both bulk and thin film have been reported [9], [10], [11], [12], [13], [14] in literature, detailed studies on the magnetic properties and variation of dielectric parameters with temperature and frequency on nanosized sample have not yet been reported. Therefore, in this report the dielectric and magnetic properties of Nd-modified BFO nanoceramics have been discussed.

Section snippets

Experimental

The nanoscale polycrystalline samples of Bi1−xNdxFeO3 (BNFO) with x=0, 0.05, 0.1 and 0.15 were prepared by metal ion complex precursor solution method using high-purity raw materials Bi(NO3)3·5H2O, Fe(NO3)3·9H2O and Nd2O3. Triethleyene amine (TEA) was used as a complexing agent. The fluffy black carbonaceous mass formed after complete evaporation of the precursor solution by heating at 200 °C was calcined for 6 h each at optimized temperatures 600, 650, 650 and 700 °C for x=0, 0.05, 0.1 and 0.15,

Structure

Fig. 1 compares the room temperature X-ray diffraction (XRD) pattern of BNFO samples with x=0, 0.05, 0.1 and 0.15. It is clear from the figure that the number of peaks and peak splitting gradually decrease on increasing Nd concentration in BNFO. All the XRD peaks of BNFO system were indexed using a standard computer program POWDMULT [15]. The hkl values are mentioned above the corresponding peaks in the figure. On the basis of best agreement between observed and calculated values of d

Conclusion

The nanoscale polycrystalline samples of a general formula BNFO with x=0, 0.05, 0.1 and 0.15 were prepared by a chemical route. Nd substitution in BFO helps in the formation of single-phase compound. The XRD patterns show that Nd substitution causes a systematic structural change in BFO. This structural change improves the dipolar ordering, reduces the conductivity there by enhancing the ferroelectric properties. Also, Nd substitution introduces ferromagnetic component in BFO.

Acknowledgments

The authors acknowledge DST, Government of India for funding the VSM. One of the authors R. K. Mishra expresses gratitude to Government of Orissa and principal of his parent college (V.N. College, Jajpur Road, Orissa) for grant of study leave to carry out this research work. Help received from Dr. Shrabanee Sen (NML, India) in preparing the sample is also acknowledged.

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