1. Magneto-Impedance Spectroscopy of Epitaxial Multiferroic Thin Films
Universidad Complutense de Madrid, Departmento de Fisicas Aplicadas III Rainer Schmidt
Magneto-Impedance Spectroscopy of
Epitaxial Multiferroic Thin Films
Rainer Schmidt, Jofre Ventura, Eric Langenberg, Manuel Varela
Grupo de Estructuras en
Capa Fina para la Espintrónica
Universidad Complutense de Madrid
Departamento Fisica Aplicada III &
Instituto de Ciencia de Materiales de Madrid
(ICMM)
Universitat de Barcelona
Departamento Fisica Aplicada i Óptica
Barcelona
C June 2011

2. Magneto-Impedance Spectroscopy of Epitaxial Multiferroic Thin Films
Universidad Complutense de Madrid, Departmento de Fisicas Aplicadas III Rainer Schmidt
Magneto-Impedance Spectroscopy of
Epitaxial Multiferroic Thin Films
Part One: Principals of Impedance Spectroscopy
Part Two:
Magneto-Impedance in Multiferroic
BiMnO3 and BiFeO3 Thin Films

3. Impedance Analyzer (Hewlett Packard 4192A)
Principals of Impedance Spectroscopy Rainer Schmidt
Impedance Analyzer (Hewlett Packard 4192A) C
Heating/
Cooling
Magnetic
Field

4. Still Useful for Interface
Principals of Impedance Spectroscopy Rainer Schmidt
Dielectric Characterisations by Impedance Spectroscopy
Well Established:
Relatively New:
Polycrystalline Bulk Material
Resistance and Capacitance from
Electrode - Sample Interface Layer
Grain Boundary Areas
Grain Interior Bulk Material
Epitaxial Thin Films
Epitaxial Layer
Electrodes
Waver Substrate
No Grain Boundaries
Still Useful for Interface
and Film Separation !!!
R. Schmidt et al., Phys.Rev.B 75 (2007) p

5. Complex Relationships
Principals of Impedance Spectroscopy Rainer Schmidt
Complex Relationships
Dielectric Permittivity – Capacitance Relationship
Contact Area A
Capacitance of the Measuring Cell in Vacuum d
Contact Distance

6. Equivalent Circuit wmax R Real – and Imaginary Parts of the Impedance
Principals of Impedance Spectroscopy Rainer Schmidt
Equivalent Circuit
ZR=R
ZC=1/iwC R
Real – and Imaginary Parts of the Impedance
Complex Impedance Plot
106
105
104
103
102
101
100
10-1
10-2
106
105
104
103
102
101
100
10-1
10-2
1.0E5
7.5e4
5.0E4
2.5E4
wmax Z'
-Z''
-Z''
Increasing Frequency
R = 100 kΩ
C = 10 nF
E E E E5
Frequency in Hz Z'

7. Equivalent Circuit IF Bulk Real Part of Capacitance Bulk IF
Principals of Impedance Spectroscopy Rainer Schmidt
Complex Impedance Plot
Interface
Bulk
Equivalent Circuit IF
Bulk
Real Part of Capacitance IF
Bulk C'
Bulk IF
G. Catalan, Appl. Phys. Lett. 88, (2006)

8. Magneto-Impedance Spectroscopy of Epitaxial Multiferroic Thin Films
Universidad Complutense de Madrid, Departmento de Fisicas Aplicadas III Rainer Schmidt
Magneto-Impedance Spectroscopy of
Epitaxial Multiferroic Thin Films
Part One: Principals of Impedance Spectroscopy
Part Two:
Magneto-Impedance in Multiferroic
BiMnO3 and BiFeO3 Thin Films

9. BiFeO3 (BFO) BiMnO3 (BMO) Ferroelectric below TCurie ~ 1125K
Impedance Spectroscopy Data: Multiferroic Thin Films Rainer Schmidt
BiFeO3 (BFO)
Ferroelectric below TCurie ~ 1125K
Ismailzade, Phys.Status Solidi B 46 (1971) K39
Antiferromagnetic below TNeel ~ 645K
Smolenskii, Yudin, Sov.Phys.JETP 16 (1963) p 622
BiMnO3 (BMO)
Ferroelectric below TCurie ~ 760 K
Kimura et al., Phys.Rev.B 67 (2003) R180401
Ferromagnetic below TCurie ~ 105K
Chiba et al., J.Solid State Chem. 132 (1997) p 139 9

10. Nb-Doped STO Substrate
Impedance Spectroscopy Data: Multiferroic Thin Films Rainer Schmidt
Sample Geometry
Copper Wires
to 1910 QuadTech
LCR Meter
Spring Loaded
Stainless-Steel
Probes
Pt - Electrodes
Film Thickness d:
50nm/100 nm
Multiferroic Layer
Nb-Doped STO Substrate
r ~ 5 mΩ·cm
AC Signal Current Path
R. Schmidt et al., Phys.Rev.B 75 (2007) p

11. Impedance Spectroscopy Data: Multiferroic Thin Films Rainer Schmidt
Temperature dependent dielectric Permittivity at fixed frequency
BiMnO3
BiFeO3
Step near 100 – 150 K
Uniform

12. Impedance Spectroscopy Data: Multiferroic Thin Films Rainer Schmidt
Frequency dependent dielectric permittivity at fixed temperature
BiMnO3
Two capacitance plateaus: indicative of two relaxations 12

13. Impedance Capacitance
Impedance Spectroscopy Data: Multiferroic Thin Films Rainer Schmidt
BiMnO3 magneto-impedance and magneto-capacitance at 95 K
Impedance
Capacitance
Dielectric permittivity
Clear magneto-resistance
Magneto-capacitance unclear 13

14. BiMnO3 magneto-capacitance at fixed frequency (95 K)
Impedance Spectroscopy Data: Multiferroic Thin Films Rainer Schmidt
BiMnO3 magneto-capacitance at fixed frequency (95 K)
Magneto-capacitance rather small, but clear trends 14

15. Impedance Capacitance
Impedance Spectroscopy Data: Multiferroic Thin Films Rainer Schmidt
BiMnO3 magneto-impedance and magneto-capacitance at 140 K
Impedance
Capacitance
Dielectric permittivity
No magneto-resistance
No magneto-capacitance 15

16. BiMnO3 magneto-capacitance at fixed frequency (140 K)
Impedance Spectroscopy Data: Multiferroic Thin Films Rainer Schmidt
BiMnO3 magneto-capacitance at fixed frequency (140 K)
No (clear) magneto-capacitance 16

17. Conclusions Impedance Spectroscopy is a useful tool for dielectric
Conclusions Rainer Schmidt
Conclusions
Impedance Spectroscopy is a useful tool for dielectric
characterization of multiferroic thin films
The Application of a magnetic field allows discrimination
of magneto-resistance and magneto-capacitance
BiMnO3 shows strong magneto-resistance and weak magneto-capacitance below the magnetic transition
BiMnO3 shows negligible magneto-resistance and magneto-capacitance above the magnetic transition

18. Random Distribution of t (Voigt Element)
Impedance Spectroscopy Rainer Schmidt
Ideal RC Element R C
Non-Ideal RC Elements
R-CPE Circuit
Random Distribution of t (Voigt Element) R
CPE

19. Complex Conductivity of an R-CPE Element
R-CPE Elements and Jonscher’s law Rainer Schmidt
Complex Conductivity of an R-CPE Element
Using
After Simplification Jonscher’s law is Obtained:

20. Random Gaussian Distribution of Relaxation Times
Gaussian Distribution of Relaxation Times Rainer Schmidt
Random Gaussian Distribution of Relaxation Times

21. Random Gaussian Distribution of Relaxation Times
Gaussian Distribution of Relaxation Times Rainer Schmidt
Random Gaussian Distribution of Relaxation Times
Dt = 7.5·10-5 s
s ' / s '(0)
Dt = 5·10-5 s
t = 1·10-4 s

22. Multiferroics Possess Two or More Ferroic Properties
Multiferroics Rainer Schmidt
Multiferroics Possess Two or More Ferroic Properties
Ferro-Electrics
Anti-Ferro-Electrics
Ferro-Magnetics
Anti-Ferro-Magnetics
Ferri-Magnetics
Ferro-Elastic
Ferro-Toroidics
¿¿¿Coupling of ferro-magnetic order and ferro-electric polarisation???
¿¿¿Switch ferro-magnetic domains with a magnetic field???

23. Magneto-Electric Effect: Coupling of Magnetic and Electric Order
Multiferroics Rainer Schmidt
Magneto-Electric Effect: Coupling of Magnetic and Electric Order
Does it
exist?
(Bi2MnNiO6)4
Kleinman et al., APS March
Meeting 2007, Abstract
Eerenstein et al., Nature 442 (2006) p 759

24. Dual Read Write Mechanism
Multiferroics Rainer Schmidt
Potential Applications of Coupled Ferromagnetic Ferroelectrics:
Dual Read(Magnetic)-Write(Electric) Mechanism in Multiferroic RAMs
Multi-State Memory H
uncoupled V
Dual Read Write Mechanism V
Magnetic Sensor
coupled

25. Ferroelectric Polarisation Measurements
Multiferroics Rainer Schmidt
Ferroelectric Polarisation Measurements
Measurement of the
Displacement Current
During Switching the
Ferroelectric Domains
Domains Switch at the
Coercive Field EC
Problem: In Real
Ferroelectrics Leakage
Current Contributes to the
Overall Measured Current
Meyer, Waser et al., Appl.Phys.Lett. 86 (2005) p

26. Ferroelectric Polarisation Measurements
Multiferroics Rainer Schmidt
Ferroelectric Polarisation Measurements
Remnant
Polarisation
Coercive
Field
Magnetic Field (Arbitrary)
Ponomarev et al., Ferroelectrics (2006) p 759
Tb2(MoO4)3 at 78 K
Wang, Viehland, Schlom, Spaldin, Rabe, Ramesh et al., Science 299 (2003) p 1719
BiFeO3 200 nm Epitaxial Layers, Room Temperature

27. Magneto-Capacitance Magnetic Field (Arbitrary)
Multiferroics Rainer Schmidt
Magneto-Capacitance H1 H2
Magnetic Field (Arbitrary)
Wang, Viehland, Schlom, Spaldin, Rabe, Ramesh et al., Science 299 (2003) p 1719
BiFeO3 200 nm Epitaxial Layers