Investigation of Magnetic Behaviour of Mechanical Activation Derived Multiferroic BiFeO 3
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0997-I08-07
Investigation of Magnetic Behaviour of Mechanical Activation Derived Multiferroic BiFeO3 Ashish Garg1, Hari Kishan Thota1, Brajesh Pandey2, and H C Verma2 1 Materials and Metallurgical Engineering, Indian Institute of Technology, Kanpur, 208016, India 2 Department of physics, Indian Institute of Technology, Kanpur, 208016, India ABSTRACT Here we report on the synthesis of multiferroic BiFeO3 ceramics by mechanical activation and detailed investigation into its magnetic behavior. The mechanically milled BiFeO3 ceramic was calcined at temperatures up to 800∞C. X-ray diffraction studies showed that the maximum amount of BiFeO3 phase forms upon calcination at 700∞C. Vibrating sample magnetometer (VSM) measurements, carried up to 1.5 Tesla, show a weak magnetic ordering in the ceramics. Measurements were also done on the samples heat treated under various cooling conditions and pronounced effect of cooling on the magnetization hysteresis curves was found. Mˆssbauer measurements suggest the presence of magnetic ordering in the samples. The nature of ordering improves upon heating from 600 to 700∞C, suggested by maximum amount of BiFeO3 phase formation at 700∞C. Magnetization vs temperature measurements show an antiferromagnetic transition at ~370∞C in the sample heat treated at 700∞C for 1hr and air cooled. INTRODUCTION: Multiferroics possess both ferroelectric and ferromagnetic (or antiferromagnetic) order in the same phase. As a result, they exhibit reversible spontaneous polarization and magnetization and often some coupling can be observed between the two [1]. Single-phase BiFeO3 (BFO) ceramic, which has ferroelectric order below a high Curie temperature (TC~830∞C) and antiferromagnetic order below a high NÈel temperature (TN~370∞C), is one of the most widely studied multiferroic materials due to its potential applications in spintronic and data storage devices [1ñ3]. However, bulk BFO suffers from high leakage current (i.e., subject to dielectric breakdown at fields 99.9% purity, Sigma Aldrich), weighed and mixed in stoichiometric proportions, were milled in a high energy planetary ball mill using ball to powder ratio of 1:1 for a period of 100 hrs. The mixture derived from mechanical activation was subjected to various heating and cooling conditions: (i) calcination at 600°C for 1 hr followed by air cooling; and calcination at 700°C for 1 hr followed by (ii) air cooling, (iii) water quenching, (iv) furnace cooling (v) furnace cooling in an oxygen atmosphere. X-ray diffraction (XRD) patterns of the milled samples after calcination were acquired using Siefert X-ray Diffractometer (Cu Kαλ: 1.54056 ≈) operated at 30 kV and 20 mA. Magnetic characterization of the calcined samples was done using a vibrating sample magnetometer (AD Magnetics-DMS-EV-7,VSM). Mˆssbauer spectroscopy analysis was carried out to investigate the magnetic ordering in the samples. RESULTS AND DISCUSSIONS X-ray diffraction patterns of BiFeO3 powders heat treated at 600 and 700°C after mechanical milling for 100 hrs are shown in figure 1
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