1. Paramagnetic Defects in Variously
Processed SrTiO3/LaAlO3 Thin Film
Structures
Duane McCrory1
Co-authors: Patrick Lenahan1, Alexander Demkov2, Andy
O’Hara2, Miri Choi2, Agham Posadas2
1Pennsylvania State University
2The University of Texas at Austin

2. n-type SrTiO3/LaAlO3 Interface
• Alternating (LaO)- and
(AlO2)+ layers within the
LaAlO2
•Alternating (SrO) and
(TiO2) layers within the
SrTiO2
Lee, J., & Demkov, A. (2008). Charge origin and localization at the n-type SrTiO3/LaAlO3
interface. Physical Review B, 78(19), 193104. doi:10.1103/PhysRevB.78.193104

3. n-type SrTiO3/LaAlO3 Interface
•What are the defects?
•Do oxygen vacancies play a dominating role?
•Are other possibly extrinsic defects important?
•Electron Paramagnetic Resonance (EPR) is unrivaled
in its analytical power to determine the physical and
chemical nature of point defects.

4. Electron Paramagnetic Resonance (EPR)
• Conventional EPR sensitivity
≈ 1010 spins.
• EPR is sensitive to defects
throughout the sample.
Microwave
Bridge
Computer
(Data Acquisition
and Field Control)
Lock-in
Amplifier
ElectromagneticModulation Coil
E
E=0 H
H = 0
E = hν
absorption
E-1/2=gβH
E+1/2=gβH
ΔE = hν=gβH
Bres
β = Bohr magneton. ν = microwave frequency. h = Planck’s constant, g = 2.0023 for a free electron
C.J. Cochrance, P.M. Lenahan, Magnetic Resonance, (2013)
• In the simplest case, an isolated
electron, resonance occurs when
hν = geβH. (ge = 2.0023219)
• Deviation from this simple
expression due to spin orbit
coupling, hyperfine interactions,
and fine structure provide its
analytical power.

5. Deviations from Simple Resonance Condition
•Spin Orbit Coupling: g factor becomes a second rank tensor.
Tensor affected by orbital angular momentum, nuclear charge,
defect symmetry, occupied and unoccupied energy levels.
•Hyperfine Interactions: Some nuclei have magnetic moments. If
a magnetic moment interacts with a paramagnetic site, the
magnetic field it generates will alter the resonance condition.
•In high spin sites, often associated with transition metal
impurities, fine structure can have an extremely large effect on
the resonance condition.

6. Deviations from Simple Resonance Condition
• g tensor: ge becomes a tensor (spin orbit coupling)
• Hyperfine: A tensor: electron interacts with nearby
magnetic nuclei (simplest case)
• Fine Structure: high spin site (general case)
Hgh  
AMHgh I 
]sin2cos3)1cos3(][2/)12[( 22
EDMHH o 
]9)1(4)1(24][2sincos)2cos)[(2/(sin 22222
 SSMMEEDHo 
}2sincos4)]cos1(2cossin){[8/1( 222222
 EEDHo 
]3)1(6)1(2[  MMSS
Ikeya, M. “New Applications of Electron Spin Resonance” (1993)

7. TE104 Microwave Double Cavity
Sample
Standard

8. Sample Geometry
(Various Processing Conditions)
SrTiO3 1 mm LaAlO3
1 mm
SrTiO3
SrTiO3
1 mm
40 nm
LaAlO3
SrTiO3
1 mm
40 nm
Structure List of Impurities from MTI Crystal
SrTiO3 Ca 20 ppm, Zn 10 ppm, Fe 20 ppm, Mg 20 ppm, Al 20 ppm
LaAlO3 Fe 2 ppm, Na 0.02 ppm, K 0.03 ppm, Zn 0.04 ppm, Si 34 ppm, Cl 76
ppm, Ca 11 ppm, Cu 2 ppm, Pb 7.5 ppm, Pr 7.5 ppm, Sm 7.5 ppm, P
0.02 ppm, Ti 0.2 ppm, Ni 0.02 ppm, Ga 0.03 ppm, Nd 7.5 ppm

9. Relevant EPR Studies on STO and LAO
in the Literature
• Badalyan, a G., Azzoni, C. B., Galinetto, P., Mozzati, M. C., Trepakov, V. a, Savinov, M., … Rosa, J.
(2007). Impurity centers and host microstructure in weakly doped SrTiO 3 :Mn crystals: new
findings. Journal of Physics: Conference Series, 93, 012012. doi:10.1088/1742-6596/93/1/012012
• Badalyan, a. G., Azamat, D., Babunts, R. a., Neverova, E. V., Dejneka, a., Trepakov, V. a., &
Jastrabik, L. (2013). EPR study of charge compensation of chromium centers in the strontium
titanate crystal. Physics of the Solid State, 55(7), 1454–1458. doi:10.1134/S1063783413070044
• Dobrov, W.I., Vieth, R.F, Browne, M. E. (1959). Electron Paramagnetic Resonance in SrTiO3.
Physical Review, 115(1), 1–2.
• Ivanova, T. A., Petrashen, V. E., Chezhina, N. V, & Yablokov, Y. V. (2002). Jahn – Teller Effect in Low-
Spin Ni 3 + in the LaAlO 3 Ceramic, 44(8), 1468–1470.
• Meierijnq, H. D. (1971). Charge Compensation by O2- Vacancies in Cr3+ Doped SrTiO3, 191, 191–
197.
• Muller, K. A. (1959). Electron Paramagnetic Resonance of Manganese IV in SrTiO3. Physical
Review Letters, 2(8), 3–5.
• Yamasaka, D., Tamagawa, K., & Ohki, Y. (2011). Effects of ultraviolet photon irradiation on the
transition metal impurities in LaAlO3. Journal of Applied Physics, 110(7), 074103.
doi:10.1063/1.3641974
• Zvanut, M. E., Jeddy, S., Towett, E., Janowski, G. M., Brooks, C., & Schlom, D. (2008). An annealing
study of an oxygen vacancy related defect in SrTiO[sub 3] substrates. Journal of Applied Physics,
104(6), 064122. doi:10.1063/1.2986244

10. SrTiO3 and SrTiO3/ SrTiO3
0 1000 2000 3000 4000 5000 6000 7000
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
Magnetic Field (Gauss)
EPRAmplitude(A.U)
STO
STO/STO
Fe3+- Vo Fe3+- Vo
Fe3+
Cr3+
Fe3+- Vo
Fe3+- Vo
Fe3+
Cr3+
Zvanut, M. E., Jeddy, S., Towett, E., Janowski, G. M., Brooks, C., & Schlom, D. (2008). An annealing study
of an oxygen vacancy related defect in SrTiO[sub 3] substrates. Journal of Applied Physics, 104(6),
064122. doi:10.1063/1.2986244
4 x1016 defects/cm3
2 x1017 defects/cm3
∆Defects = 1.6 x1017 defects/cm3
STO
STO/STO

11. LaAlO3 and SrTiO3/ LaAlO3
• Tentative
Identification:
Mostly transition
metal impurity
coupled sites
with long spin-
lattice relaxation
times.
0 1000 2000 3000 4000 5000 6000 7000
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
EPRAmplitude(A.U.)
Magnetic Field (Gauss)
1x1017 defects/cm3
LAO
8 x1017 defects/cm3
100nm STO/LAO
∆Defects = 7 x1017 defects/cm3

12. SrTiO3/LaAlO3 - Vacuum Anneal and No
Vacuum Anneal
0 1000 2000 3000 4000 5000 6000 7000
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
Magnetic Field (Gauss)
EPRAmplitude(A.U.)
3% electron activation
11% electron activation
Vacuum Anneal
No Vacuum Anneal
4 x1017 defects/cm3
1 x1017 defects/cm3

13. Conclusion
• Large number of extrinsic defects within the structure,
as evidence of fine structure suggesting that most of
them involve transition metal impurity sites with
relatively long spin-lattice relaxation times.
• The density of these extrinsic defects is tremendously
altered by processing conditions involved in deposition
of SrTiO3.
• Any discussion of the role of the addition of dopants,
introduction of simple point defects such as oxygen
vacancies or oxygen interstitials should take into
account the large number of extrinsic processing
dependent point defects.