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 C17- 14. June 2011

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

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

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.245111

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

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 101 102 103 104 105 106 107 108 0 2.5E4 5.0E4 7.5E4 1.0E5 Frequency in Hz Z'

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, 102902 (2006)

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

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

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.245111

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

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

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

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

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

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

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

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

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:

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

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

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???

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

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

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 142907

Ferroelectric Polarisation Measurements Multiferroics Rainer Schmidt Ferroelectric Polarisation Measurements Remnant Polarisation Coercive Field Magnetic Field (Arbitrary) Ponomarev et al., Ferroelectrics 43-48 (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

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