Properties of Ilmenite-Hematite Ferromagnetic Semiconductors · Center For Materials For...
Transcript of Properties of Ilmenite-Hematite Ferromagnetic Semiconductors · Center For Materials For...
Center For Materials For Information TechnologyAn NSF Materials Research Science and Engineering CenterThe University of Alabama
Properties of Ilmenite-Hematite Ferromagnetic Semiconductors
D. Allen, P. Padmini, H. Alouach, R. Schad, W. Butler and R.K. Pandey
Center For Materials For Information TechnologyAn NSF Materials Research Science and Engineering CenterThe University of Alabama
Ilmenite - FeTiO3
• Oxide wide bandgap semiconductor;
p-type, Eg = 2.58 eV.
• Antiferromagnetic, TN = 57 K
• Ferroelectric, Tc ≅ 600 K
• Excellent radiation resistant material
• A dominant mineral on lunar surface
Center For Materials For Information TechnologyAn NSF Materials Research Science and Engineering CenterThe University of Alabama
Ilmenite - Hematite (I-H) solid solutions
(FeTiO3)(1-x).(Fe2O3)x show, depending on
concentration x:
• Semiconducting properties (p or n type)
• Ferrimagnetic or antiferromagnetic properties -
Tc or TN > room temperature
• Radiation resistant system (Neutrons)
Center For Materials For Information TechnologyAn NSF Materials Research Science and Engineering CenterThe University of Alabama
Ceramic Processing(1-x)FeTiO3.xFe2O3
Isostatic pressing @ 40000 psi
X = 0 to 0.67
FeTiO3+Fe2O3
Ball Milling
Sintering @1200C, 12h in Ar
Targets of (1-x) FeTiO3.xFe2O3 ceramics
Center For Materials For Information TechnologyAn NSF Materials Research Science and Engineering CenterThe University of Alabama
Pulsed Laser Deposition
Excimer Laser of wavelength 248 nm
Target : (1-x)FeTiO3.xFe2O3, x = 0 - 0.67
Substrate-Target distance : 3-5 in
Laser energy : 300 - 800 mJ
Substrate temperature : 650 - 850°C
Base Pressure : 1x10-6 Torr
Gas : Ar/O2
Center For Materials For Information TechnologyAn NSF Materials Research Science and Engineering CenterThe University of Alabama
BULK PROPERTIES OF IH
Center For Materials For Information TechnologyAn NSF Materials Research Science and Engineering CenterThe University of Alabama
Resistivity Measurement
0
1
2
3
4
5
6
7
8
0 50 100 150 200 250 300 350
x=0x=0.1x=0.2x=0.33x=0.45x=0.67
log
resi
stiv
ity (O
hm-c
m)
T(K)
Resistivity as a function of temperature for (1-x)FeTiO3.xFe2O3
0
50
100
150
200
250
300
350
400
0 0.1 0.2 0.3 0.4 0.5
UnradiatedRadiated
Res
istiv
ity@
RT (O
hm-c
m)
Comp- x-Fe2O
3
Resistivity @ R.T as afunction of composition
Center For Materials For Information TechnologyAn NSF Materials Research Science and Engineering CenterThe University of Alabama
Seebeck Measurement
Seebeck coefficient as a function of composition and temperature
X < 0.2 – p type; and x > 0.2 – n type
-200-150-100-50
050
100150200
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
S(uV
/K)
Composition, xFe2O
3
n
p
-200
-100
0
100
200
300
150 200 250 300 350 400
S(x=0)S(x=0.1)S(x=0.2)S(x=0.27)S(x=0.33)S(x=0.45)S(x=0.67)
S(uV
/K)
T (K)
p
n
Center For Materials For Information TechnologyAn NSF Materials Research Science and Engineering CenterThe University of Alabama
Magnetic Measurements
0.0 0.2 0.4 0.6 0.8 1.00
20
40
60
80
100
120
140
160
180
200
0
200
400
600
800
1000
FM
AF
AF
M @
300K
and
->0K
,10kO
e (em
u/cm
3 )
composition xopen symbols: Ishikawa, Akimoto J.Phys.Soc.Jap.12, 1083 (1957)
Tc and T
N (K)
Magnetic moment and transition temperature fordifferent compositions of Ilmenite-Hematite
Center For Materials For Information TechnologyAn NSF Materials Research Science and Engineering CenterThe University of Alabama
Magnetic Measurements
0 100 200 300 400 500 6000
10
20
30
40
50
60
temperature (K)
M@
10kO
e (e
mu/
g)
composition: 0% 20% 33% 45%
radiation:Dose: 4.4 x 1010 n/cm2
Energy: 73MeV (ave)empty: beforefilled: after
Magnetic moment before and after neutron irradiation
Center For Materials For Information TechnologyAn NSF Materials Research Science and Engineering CenterThe University of Alabama
THIN FILMS OF IH
Center For Materials For Information TechnologyAn NSF Materials Research Science and Engineering CenterThe University of Alabama
Structural Characterization
0
50
1 00
1 50
2 00
2 50
3 00
3 50
4 00
3 6 38 40 42 4 4
20 729 -1 2 tw
inte
nsity
(c
ps)
2θ (deg)
A l2 O 3(0006)
IH (0006)
20 30 40 50 60 70 80 90 1000
500
1000
1500
2000
MgO
0 0 0 122 0 -2 2
MgO
0 0 0 6
inten
sity
(cps
)
2θ (deg)
X-ray diffraction of IH film on Sapphire (c-cut) and MgO
Center For Materials For Information TechnologyAn NSF Materials Research Science and Engineering CenterThe University of Alabama
Optical Characteristics
Transparent Ilmentite/hematite films on MgO
33nm (FeTiO3)0.80 (Fe2O3)0.2019nm (FeTiO3)0.67 (Fe2O3)0.33
Center For Materials For Information TechnologyAn NSF Materials Research Science and Engineering CenterThe University of Alabama
Electrical Characterization
0
0.5
1
1.5
2
2.5
3
3.5
150 200 250 300 350
650C850C
log
resi
stiv
ity (o
hm-c
m)
T(K)
-100
-80
-60
-40
-20
0
240 260 280 300 320 340 360
S(uV
/K)
T(K)
Resistivity of x=0.45 film on MgO at two different deposition temperature
Seebeck Coefficient of x = 0.45 film on MgO
Center For Materials For Information TechnologyAn NSF Materials Research Science and Engineering CenterThe University of Alabama
Magnetic Characterization
-10000 -8000 -6000 -4000 -2000 0 2000 4000 6000 8000 10000-2.0x10-4
-1.5x10-4
-1.0x10-4
-5.0x10-5
0.0
5.0x10-5
1.0x10-4
1.5x10-4
2.0x10-4
c33emu10a c33emu100b c33emu200b c33emu290a c33emu290b
mag
netic
mom
ent (
emu)
magnetic field (Oe)
0
10
20
30
40
50
60
70
80
0 0.1 0.2 0.3 0.4 0.5M
s @
300
K (e
mu/
cc)
Comp - xFe2O
3
Bulk
Film
Magnetic properties of x = 0.33 film on MgO
Magnetic moment as a function of composition
Center For Materials For Information TechnologyAn NSF Materials Research Science and Engineering CenterThe University of Alabama
Conclusions
• (1-x)FeTiO3.xFe2O3; x < 0.2 - p-type and x > 0.2 -n-type• x < 0.1 - antiferromagnetic; 0.1 < x < 0.67 –ferrimagnetic • Resistivity decreased after neutron irradiation• Magnetic moments enhanced by neutron irradiation.• Highly textured and transparent films on MgOand sapphire
Center For Materials For Information TechnologyAn NSF Materials Research Science and Engineering CenterThe University of Alabama
Future Work
• Optimization of the deposition parameters to get a good epitaxial film.• Bandgap measurements• Polycrystalline films to evaluate the varistorproperty.• pn junction devices• Characterize films for Ferroelectric and Magnetic properties.