Ivane Javakhishvili Tbilisi State University

Institute of Condensed Matter Physics

Giorgi Khazaradze

M Synthesis and Magnetic Properties of Multiferroic BiFeO3

Tbilisi, 2012A

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.

FFerromagnetic ordering

Ferroelectric ordering

BiFeO3 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 BiFeO3. Pink-bismuth, Blue-iron, Green-oxygen.

Problem

BiFeO3 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 8800C)

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 BiFeO3

1/2 Bi2O3 + 1/2Fe2O3 = BiFeO3

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 kWt power each.

X-ray diffraction pattern of multiferroic BiFeO3

Magnetization measurements were performed on the SQUID-magnetometer (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

-4000 -2000 0 2000 4000-0.2-0.10.00.10.20.30.40.50.60.70.8

-800 0 800

-0.06

0.00

0.06

Field(Oe)

Mag

netic

mom

ent (

emu/

g)

BiFeO3

T=5K

Magnetization (M) versus field (H) curve for the BiFeO3

powder measured at 5 K. Inset shows the details of the M–H hysteresis loop displayed at a field of 1000 Oe.

-4000 -2000 0 2000 4000

-0.06

-0.04

-0.02

0.00

0.02

0.04

0.06

Mag

netic

mom

ent (

emu/

g)

Field (Oe)

BiFeO3

T=300K

Magnetization (M) versus field (H) curve for the BiFeO3

powder measured at 300 K.

For the study of microscopic magnetic properties of the prepared BiFeO3 the sample EPR spectra were measured in a broad temperature range.

EPR spectrometer BRUKER ER 200D-SRC

EPR measurements

1000 2000 3000 4000 5000 6000

-0.3

-0.2

-0.1

0.0

0.1

0.2E

SR

, a,u

Magnetic field,G

BiFeO3

T=291k

1000 2000 3000 4000 5000 6000

-0.3

-0.2

-0.1

0.0

0.1

0.2

ES

R, a

.u

Magnetic field,G

BiFeO3

T=410K

1000 2000 3000 4000 5000 6000-0.12

-0.10

-0.08

-0.06

-0.04

-0.02

ES

R, a

.u

Magnetic Field,G

BiFeO3

T=650K

1000 2000 3000 4000 5000 6000

-0.35

-0.30

-0.25

-0.20

-0.15

-0.10

-0.05

0.00

ES

R, a

.u

Magnetic field,G

T=700K

BiFeO3

300 400 500 600 7000

350

700

1050

1400

1750

2100

Temperature (K)

BiFeO3

H (G

)

300 400 500 600 7003000

3150

3300

3450

3600

3750

3900

Hr (G

)

Temperature (K)

Hr1

Hr2

Hr3

BiFeO3

300 400 500 600 7000

4000

8000

12000

16000

Inte

nsity

Temperature (K)

I1

I2

I3

BiFeO3

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 BiFeO3 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 BiFeO3 compound using photostimulated solid-state reaction method.

5. With further optimization of synthesis conditions it should be possible to synthesie 100 % phase pure BiFeO3 compound.

Thanks for attention!