Ivane Javakhishvili Tbilisi State University Institute of Condensed Matter Physics Giorgi Khazaradze M Synthesis and Magnetic Properties of Multiferroic BiFeO 3 Tbilisi, 2012 A

Collaboration M Supervisor : Professor Alexander Shengelaya Dr. D. Daraselia Tbilisi State University Dr. D. Japaridze Tbilisi State University Z. Guguchia University of Zürich A

Introduction In the 1960’s it was discovered a new class of materials, where ferromagnetic and ferroelectric ordering coexist. They were called multiferroics. F Ferromagnetic ordering Ferroelectric ordering

BiFeO 3 has rhombohedrally perovskite structure. At the same time quite diversified and uncommon properties: ferroelectric transition at T c =1103 K and antiferromagnetic transition at T N =643 K. Crystal structure of BiFeO 3. Pink-bismuth, Blue-iron, Green-oxygen.

Problem BiFeO 3 samples are usually obtained by thermal solid-state reaction method. It takes many hours to prepare these samples. However, impurity phases are usually present. Recently clean samples were obtained with rapid liquid phase sintering method. This method implies heating of the sample for a short time above its melting temperature. (During 5 minute at C) Y.P. Wang et al. Appl.Phys.lett. 10, 11 (2004).

Recently a new method was developed in our group at Tbilisi State University. The samples are irradiated wish strong beam of photons. It was called a photostimulated solid-state reaction method. With this method it takes only few minutes to prepare the samples. The negative effects of longtime thermal process are decreasing to a minimum due to small time. Also the energy consumption decreases significantly. New idea:

Preparation of BiFeO 3 1/2 Bi 2 O 3 + 1/2Fe 2 O 3 = BiFeO 3 Mixing of starting materials. Pressing into pellet. I rradia ti on by photon-beam furnace with strong beam of photons, during two minutes at C.

Experimental Methods A photon-beam furnace in switched mode. The furnace containes 10 halogen lamps with 1 kWt power each.

X-ray diffraction pattern of multiferroic BiFeO 3

Magnetization measurements were performed on the SQUID- magnetometer (Superconducting Quantum Interference Device) in the temperature range of K and up to 7 Tesla magnetic field. Performed magnetic measurements: 1.Temperature scan (TScan) in 2000 G applied magnetic field. 2.Field scan (FScan) at 5 K and 300 K.

Dependence of magnetic moment on temperature in 2000 G applied magnetic field

Magnetization (M) versus field (H) curve for the BiFeO 3 powder measured at 5 K. Inset shows the details of the M–H hysteresis loop displayed at a field of 1000 Oe.

Magnetization (M) versus field (H) curve for the BiFeO 3 powder measured at 300 K.

For the study of microscopic magnetic properties of the prepared BiFeO 3 the sample EPR spectra were measured in a broad temperature range. EPR spectrometer BRUKER ER 200D-SRC EPR measurements

The intensity, linewidth and resonance fields for both EPR lines as a function of temperature was obtained and is plotted on the following graphs.

Conclusions 1. We prepared BiFeO 3 with photostimulated solid-state reaction method. 2. We studied its magnetic properties using SQUID magnetometer. 3. For the first time EPR spectra were measured in broad temperature range and sharp changes of EPR signal were observed at the antiferromagnetic transition temperature. 4. Obtained results show that it is possible to synthesize quite good quality BiFeO 3 compound using photostimulated solid-state reaction method. 5. With further optimization of synthesis conditions it should be possible to synthesie 100 % phase pure BiFeO 3 compound.

Thanks for attention!