1、Resistance and transport behavior accompanying polarization switching in BFO,Presented by: Rongli Gao,Group M03 State Key laboratory of magnetism Institute of Physics,Supervisor: Prof. Jirong Sun,2012-12-24,Content,1. Background and Motivation 2. Experiments 3. Results and discussion 4. Summary,Back

2、ground and Motivation,BiFeO3: multiferroic material,JPCM 20 (2008)434220; Nature Materials 5 (2006) 823,(1) G-type antiferromagnetic order: With TN643K ; weak ferromegnetism,J. Wang et. al, Science.299, 1719(2003),(2)Ferroelectric order: with Tc1100K; Large polarization Pr 100uC/cm2,Polarization alo

3、ng (111) direction,Pseudo cubic structure with c/a=1.016,H. T. Yi et. al, Adv. Mat. 23,3403(2011);,Switchable rectifying behavior and photovoltaic effect,Background and Motivation,C. Wang et al, APL. 98,192901(2011);,D. Lee et al, PRB 84,125305(2011),(1) Rectifying behavior is interesting due to its

4、 potential application in the non-volatile memory technology. (2) However, switchable rectifying and transport behaviors occur accompanying polarization changes and the polarization were considered only in fully upward or fully downward polarized states. (3) Few works have been made about the rectif

5、ying and transport behavior and the intermediately polarized states. (4) The influence of polarization fatigue process on photo-current has not been studied yet.,Background and Motivation,Sample structures: Ag/Bi0.9La0.1FeO3/La0.7Sr0.3MnO3/SrTiO3,Experiments and Results,Methods: pulse laser depositi

6、on (PLD) (a) LSMO films as bottom electrodes were deposited on SrTiO3 (STO) substrates. (Temperature:700；oxygen pressure:50Pa; deposition frequency of 1Hz; with the laser energy of 1.2 J/cm2),(b) BLFO films were deposited on LSMO buffer layer.(Temperature:650 ；oxygen pressure:15Pa; deposition freque

7、ncy of 1Hz; with the laser energy of 1.2 J/cm2 ; cool down to RT at 2/min in the atmosphere of 100Pa),(c) Ag films were deposited by on BLFO as the top electrode.( 10-4Pa),1. XRD data,(a) BLFO target,(b) BLFO/LSMO/STO film,Results and discussion,2. P-E curves,The（100）and（110）oriented Pr is about 80

8、and 95 uC/cm2 respectively,(c) BLFO-LSMO/STO-(100),(d) BLFO-LSMO/STO-(110),3. Transport behaviors accompanying polarization switching,where S is the area of the top electrode,According to,We can calculate the Pr value,3.1. Polarization switching process dependence on the pulse voltages (PV curve),(a

9、) Transient current time,(b) Polarizarion (Pr) voltage (V),3.2. I-V curves,(a) I-t curve from downward to upward,(b) I-t curve from upward to downward,(c) I-Vcurve from downward to upward,(d) I-V curve from upward to downward,The current maximum (resistive minimum) occurs at the coercive voltage, bo

10、th in upward and downward flipping.,In general, the transport behavior is determined by the Schottky barrier formed at the interface.,(a),(b),(c),(d),Therefore, should demonstrate a monotonic variation with Pr. The resistance R should varied monotonically with the polarization. Indicating that Pr in

11、duced barrier variation may not limited to the interfacial barrier.,1 L. Pintilie et. al, JAP.98, 124103(2005),The barrier height was varied by the polarization1:,Where,is the separation between surface polarization charge and electrode,is the static dielectric constant,In order to illustrate this a

12、bnormal relation, fatigue test was performed.,3.3. Polarization-Switching and fatigue properties,(a) alternative pulse,R of both upward and downward polarization was decreasing with repeating alternative pulses,(b) identical pulse,Schematic of barrier structure,This just explains why the current lev

13、el is low/high under positive/negative bias, but the abnormal result was still unknown. The impedance spectra was studied.,R of both upward and downward polarization was increasing with repeating identical pulses,3.4. impedance spectra analysis,(a) the schematic of the circuit,According to,and,For a

14、 parallel RC circuit, the modulus M should be,(b) The imaginary part of the frequency-dependence,Only a single peak can be described by a single RC equivalent circuit, and the peak position and height have the form of 1/RC and C0/2C.,(c ) Cole-cole plots,(a) Schematic domain structure of the LBFO fi

15、lm after alternative or identical pulse treatment. Local leakage paths form along the conductive domain walls. (b) Variation of Pr under different pulse treatments.,(a),(b),Analysis,Leakage paths form along the conductive domain walls, the resistance of domain walls is small and facilitate electron

16、moving. Pr reduce up to 7% after 4000 alternative pulses. Some domain walls pinned and reduced polarization.,Ag/LBFO/LSMO/STO heterojunctions were fabricated by pulse laser deposition (PLD) method Polarization-modulated switching behavior and fatigue phenomenon have been investigated. A complex depe

17、ndence of device resistance on poling voltage is observed. Bipolar and unipolarelectric pulses produce different effects on the transport propertyof the device. The former enhances the rectifying characteristics of the device, hereas the latter produces a reverse effect. Different polarization state

18、s can be obtained by selecting appropriate poling voltages, novel application was anticipated according to tuning the polarization state.,Summary,Publications List,Complex transport behavior accompanying domain switching in La0.1Bi0.9FeO3 sandwiched capacitors R. L. Gao, Y. S. Chen, J. R. Sun, Y. G. Zhao, J. B. Li, B. G. Shen, Applied Physics Letters. 101,152901(2012) 2. Exchange bias in (110)- orientated Bi0.9La0.1FeO3/La0.5Ca0.5MnO3 films J. L. Zhao, R. L. Gao, W. W. Gao, B. G. Shen, J. R. Sun Physica B.407,2773, (2012) . 3. The effect of