Microwave Responce from La- and Dy- doped BiFeO 3 Thin Films
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0966-T05-08
Microwave Responce from La- and Dy- doped BiFeO3 Thin Films Peter Kr. Petrov1, Vaijayanti R Palkar2, Neil McN Alford1, Alexander K Tagantsev3, K Prashanthi4, Hsin-I Chien1, Anna-Karin Axelsson1, and S Bhattacharya2 1 London South Bank University, London, SE1 0AA, United Kingdom 2 Tata Institute of Fundamental Reasearch, Mumbai, 400005, India 3 EPFL, Lausanne, CH-1015, Switzerland 4 Indian Institute of Technology Bombay, Mumbai, 400076, India
ABSTRACT The dielectric response of La- and Dy- doped BiFeO3 thin films to electric- and magnetic fields was measured at microwave frequencies (up to 12GHz) in a temperature range from 25 oC to 300 oC. Interesting phenomena were observed. Significant oscillations in the C(f) characteristic which were unaffected by the electric field or by elevated temperature but which were dampened by a magnetic field. We also observed ‘N’-type I-V characteristics. A possible explanation for this mesoscopic response is the presence of structural features that cause resonance (e.g. grains, grain-boundaries, domains, domain walls etc), with a contribution strong enough to be averaged by the system. The exact origin of these features is unknown at present. INTRODUCTION Multiferroic materials are these where more than one ferroic order (magnetic, electric, elastic) co-exists and are coupled [1]. BiFeO3 (BFO) as one of the very few single-phase multiferoic material is subject to increased scientific interest [2-4]. The challenges with BiFeO3 come from the fact that at room temperatures bulk BFO is ferroelectric and antiferromagnetic [3], as well as its large leakage current[4]. In this work dielectric properties of enhanced BFO thin films were investigated at microwave frequency. To enhance BFO magnetization and induce ferromagnetism, samples were doped with Dy at Bi site. It does not alter the crystal structure or destroy ferroelectricity. Also, it is known that BFO with a perovskite structure has a significantly reduced leakage current. However, the temperature window for obtaining the perovskite phase is very narrow [2]. La doping helps to stabilize the phase [4] and hence to reduce leakage current, therefore in one sample in addition to Dy, La was also added. EXPERIMENT Thin films of Bi0.7Dy0.3FeO3 and Bi0.6La0.1Dy0.3FeO3 were deposited on single crystal LaAlO3 and MgO substrates using pulsed laser deposition (PLD). PM882 GSI-Lumonics, 248 KrF excimer laser was used for the ablation process. For the deposition, stoichiometric targets of Bi0.7Dy0.3FeO3 and Bi0.6La0.1Dy0.3FeO3, synthesized by a partial co-precipitation route were used. NaOH was used as the precipitating agent. The precipitate was filtered out, washed and then
dried under infra-red lamp. The dried powders were pulverized and calcined at 600oC for 1 hour to obtain the reacted material. The calcined powder was pressed to form a pellet and sintered at 800oC for 2 hours to obtain a dense target for laser ablation. Pulsed laser ablation conditions, were optimized to achieve phase-pure, granular, homogeneous and insulatin
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