Properties of Ilmenite-Hematite Ferromagnetic Semiconductors · Center For Materials For...

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Properties of Ilmenite-Hematite Ferromagnetic Semiconductors

D. Allen, P. Padmini, H. Alouach, R. Schad, W. Butler and R.K. Pandey


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


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)


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


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


BULK PROPERTIES OF IH


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


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


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


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


THIN FILMS OF IH


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


Optical Characteristics

Transparent Ilmentite/hematite films on MgO

33nm (FeTiO3)0.80 (Fe2O3)0.2019nm (FeTiO3)0.67 (Fe2O3)0.33


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


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


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


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.

Properties of Ilmenite-Hematite Ferromagnetic Semiconductors · Center For Materials For...

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