Ivane Javakhishvili Tbilisi State University Institute of Condensed

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

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

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

Bi. Fe. O 3 has rhombohedrally perovskite structure. At the same time quite diversified and uncommon properties: ferroelectric transition at Tc=1103 K and antiferromagnetic transition at TN=643 K. Crystal structure of Bi. Fe. O 3. Pink-bismuth, Blue-iron, Green-oxygen.

Problem Bi. Fe. O 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 8800 C) Y. P. Wang et al. Appl. Phys. lett. 10, 11 (2004).

New idea: 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.

Preparation of Bi. Fe. O 3 1/2 Bi 2 O 3 + 1/2 Fe 2 O 3 = Bi. Fe. O 3 Mixing of starting materials. Pressing into pellet. Irradiation by photon-beam furnace with strong beam of photons, during two minutes at 8800 C.

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

X-ray diffraction pattern of multiferroic Bi. Fe. O 3

Magnetization measurements were performed on the SQUIDmagnetometer (Superconducting Quantum Interference Device) in the temperature range of 2 -300 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 Bi. Fe. O 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 Bi. Fe. O 3 powder measured at 300 K.

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

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 Bi. Fe. O 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 Bi. Fe. O 3 compound using photostimulated solid-state reaction method. 5. With further optimization of synthesis conditions it should be possible to synthesie 100 % phase pure Bi. Fe. O 3 compound.

Thanks for attention!