Post on 16-Dec-2015
Ivane Javakhishvili Tbilisi State University
Institute of Condensed Matter Physics
Giorgi Khazaradze
M Synthesis and Magnetic Properties of Multiferroic BiFeO3
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.
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.
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.
-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)
Ma
gn
etic
mo
me
nt (e
mu
/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
Ma
gn
etic
mo
me
nt (
em
u/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.