Home| 題 目 |
Multiferroic Transitions and Magnetoelectric Coupling in BiFeO3 |
| 講 師 | Dhananjai Pandey (School of Materials Science and Technology, Banaras Hindu University, India） |
| 日 時 | 2009年7月2日( 木) 14:30 －16:00 |
| 場 所 | 理学研究科 物理科学専攻 会議室 C212 |
| 要 旨 |
Multiferroic materials exhibit simultaneously at least two different types of ferroic orders characteristic of ferroelectric, magnetic and ferroelastic phases. The phenomena of magnetic and ferroelectric orderings have been generally regarded as “mutually excusive” in oxide perovskites. Their coexistence in some magnetoelectric multiferroics has therefore evoked tremendous interest in recent years because of the interesting underlying physics and also the possibility of designing new generation sensor, actuator and memory devices.
BiFeO3 is the only room temperature multiferroic with magnetic and ferroelectric transitions occurring at TN ~ 643 K and TC ~ 1103 K. The observation of an anomaly in the dielectric constant at the magnetic transition temperature is often taken as an evidence of magnetoelectric coupling of multiferroic origin. It has, however, been pointed out that such a dielectric anomaly may also result from magnetoresistive contributions due to space charge polarizations, especially in granular systems. It does not therefore necessarily provide evidence for intrinsic magnetoelectric coupling of multiferroic origin. In the (Bi1-xAx) (Fe1-xTix)O3 (A = Ba2+, Pb2+) systems, we have recently shown1,2 that the temperature variation of the high frequency dielectric constant, free from space charge contributions, still exhibits an anomaly at the magnetic transition temperature. Further, it is accompanied with a pronounced change in the lattice parameters at the magnetic transition temperature revealing strong magnetoelastic coupling. More interestingly, there is a significant shift in the atomic positions below the magnetic transition temperature. We have shown that these shifts are due to a rare type of isostructural phase transition driven by one of the irreps of the ferroelectric space group. The ionic polarization calculated form the positional coordinates of the atoms in the unit cell is not only found to increase in the magnetic phase but also scale linearly with magnetization. Our observations provide the first direct and atomic level evidence for intrinsic magnetoelectric coupling of multiferroic origin in BiFeO3 based systems. 1) A. Singh et al, Phy. Rev. Lett. 101, 247602 (2008). 2) S. Bhattacharjee et al, Appl. Phys. Lett. 94 012906 (2009).
|
|
担 当 |
黒岩 芳弘 （理学研究科）・内線7397 |
5研究科共同セミナーの認定科目です
＊５研究科共同セミナーの単位認定等につきましては、所属研究科の学生支援窓口にてご確認ください。
後援 先進物質機能研究センター
