Role of annealing conditions on the ferromagnetic and dielectric properties of La 2 NiMnO 6
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S.K. Deshpande UGC-DAE Consortium for Scientific Research, Bhabha Atomic Research Centre, Mumbai 400085, India
P.S.R. Krishna Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India
S. Chatterjee and P. Ayyub Department of Condensed Matter Physics, Tata Institute of Fundamental Research, Mumbai 400005, India
A.K. Tyagib) Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400085, India (Received 5 September 2010; accepted 20 December 2010)
La2NiMnO6 (LNMO) was prepared by a combustion method followed by heating at high temperature. Subsequently, the preformed LNMO was annealed in air, oxygen, or N2 atmosphere and characterized by powder x-ray diffraction (XRD), neutron diffraction, superconducting quantum interference device magnetometry, and dielectric analysis. Structural studies by XRD and neutron diffraction revealed the coexistence of partially cation disordered monoclinic (31%) and rhombohedral (69%) phases in the sample annealed in air. However, the sample annealed in oxygen shows about 50:50% of monoclinic and rhombohedral phases. Relaxor-like behavior with relative permittivity of the order of 104 was observed in the sample annealed in air, while relative permittivity decreases to about 200 in samples annealed in oxygen atmosphere. The magnetic properties indicate a well-defined ferromagnetic phase in the oxygen-annealed sample compared to a feeble ferromagnetic signature in the air-annealed one. The dielectric and ferromagnetism of LNMO samples have been related to formation and annihilation of oxygen vacancies.
I. INTRODUCTION
Recent interests on magnetoelectric materials are focused on the materials exhibiting simultaneous ferro/ antiferromagnetic and ferroelectric (multiferroics) properties due to their wide range of possible applications in electronic devices.1,2 A large number of materials with lone pair containing elements, like Pb2+, Bi3+, etc., are being explored for coupled electric and magnetic polarization. In the aspect of lead-free environment friendly materials, significant attention had been paid to perovskite (ABO3, A 5 rare earth, Bi3+; B 5 transition metal ions like Fe, Mn, Cr, etc.) type materials and in particular on BiFeO3 and BiMnO3 due to their intrinsic high Curie temperature ferroelectric nature.3–8 Similarly, a large magnetoelectric effect has been reported in hexagonal RMnO39 and RMn2O5,10 where R 5 rare-earth cation type materials have also been investigated. The role of magnetic frustration has been attributed to the enhanced
Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/jmr.2011.4 J. Mater. Res., Vol. 26, No. 4, Feb 28, 2011
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magnetoelectric coupling in these materials. However, the intrinsic antiferromagnetic nature of BiFeO3 and RMnO3 compositions or low ferromagnetic transition temperature of BiMnO3 restricts the practical importance of these materials. In addition, these simple perovskites, R2BB9O6 (R 5 rare
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