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[ISSP Colloquiums]
Ferroelectricity and Spintronics at Nanoscale
Title : Ferroelectricity and Spintronics at Nanoscale
Date :
Time :
2008/7/10(Thu)
2:00 PM -  
Place : Lecture Room (A632), 6th Floor, ISSP   
Lecturer : Prof. Renat Sabirianov
Affiliation : University of Nebraska
Summary : Ferroelectric materials are very promising for various technological applications such as dynamic random access memories and non-volatile binary data storage media. A continuing demand to further miniaturize electronic devices brings up a problem of the existence of ferroelectricity on a nanometre scale. Recent experimental results demonstrate that in thin films ferroelectricity persists down to film thickness of a few unit cells, which opens an avenue for novel electronic devices based on ultrathin ferroelectrics. These findings raise a question about factors controlling ferroelectricity and the nature of the ferroelectric state at the nanoscale. I will discuss a first-principles study of ferroelectric thin films placed between two metal electrodes, either SrRuO3 or Pt. The results show that bonding at the ferroelectric-metal interface imposes severe constraints on the displacement of atoms, destroying the bulk tetragonal soft mode in thin ferroelectric films. This does not, however, quench local polarization. Although the critical thickness for the net polarization of the KNbO3 film, for example, is finite – about 1 nm for Pt and 1.8 nm for SrRuO3 electrodes – local polarization persists down to thickness of a unit cell.[1] The oppositely-oriented dipole moments at the two interfaces have opposite directions for Pt and SrRuO3 electrodes, making the potential profile asymmetric in ferroelectric junctions with different electrodes. These metal/ferroelectric/metal junctions may exhibit bi-stable resistive switching with resistances in low and high resistance states differ by orders of magnitude.[2] These results are encouraging in view of potential applications of ferroelectric tunnel junctions as a two-terminal non-volatile memory device. Using magnetic electrodes gives a possibility of forming 4-state logic devices. I will discuss the similarities and differences of such devices based on ferroelectric and electroresistive oxide tunnel junctions.[3]

1. Chun-gang Duan, R. F. Sabiryanov, W.-N. Mei, S. S. Jaswal,and E. Y. Tsymbal," Interface-Controlled Ferroelectricity at the Nanoscale", Nano Letters, 6, 483 (2006)
2. M. Ye. Zhuravlev, R. F. Sabirianov, S. S. Jaswal,and E. Y. Tsymbal, "Giant Electroresistance in Ferroelectric Tunnel Junctions", Phys. Rev. Lett. 94, 246802 (2005)
3. A. Sokolov, R.F. Sabirianov, I.F. Sabirianov, B. Doudin, "Magnetic nano-filaments as model systems for electro-resistance switching with magneto-resistance signature", submitted
Contact : Osamu Sugino (ext.63290)