| Project/Area Number |
16340109
|
|---|
| Research Category |
Grant-in-Aid for Scientific Research (B)
|
| Allocation Type | Single-year Grants |
|---|
| Section | 一般 |
|---|
| Research Field |
Condensed matter physics II
|
|---|
| Research Institution | Aoyama Gakuin University |
|---|
Principal Investigator |
FURUKAWA Nobuo Aoyama Gakuin University, College of Science and Engineering, Associate Professor, 理工学部, 助教授 (00238669)
|
|---|
| Co-Investigator(Kenkyū-buntansha) |
MOTOME Yukitoshi University of Tokyo, Department of Applied Physics, Associate Professor, 大学院工学系研究科, 助教授 (40323274)
KUBO Kenn Aoyama Gakuin University, College of Science and Engineering, Professor, 理工学部, 教授 (30015862)
|
|---|
| Project Period (FY) |
2004 – 2006
|
| Project Status |
Completed (Fiscal Year 2006)
|
| Budget Amount *help |
¥8,000,000 (Direct Cost: ¥8,000,000)
Fiscal Year 2006: ¥1,200,000 (Direct Cost: ¥1,200,000)
Fiscal Year 2005: ¥1,200,000 (Direct Cost: ¥1,200,000)
Fiscal Year 2004: ¥5,600,000 (Direct Cost: ¥5,600,000)
|
|---|
| Keywords | Strongly correlated electron system / Strongly correlated electronics / spintronics / 二重交換系 / 希薄磁性半導体 / 表面・界面 / 磁性 / 電気伝導 / 不均一系 / 乱れ / 揺らぎ |
|---|
| Research Abstract |
1) We developed the polynomial-expansion Monte Carlo method for electron systems which are interacting with classical degrees of freedom. By applying this new method, we studied generalized double-exchange models in order to investigate the origin of the colossal magnetoresistance in manganese oxides. We investigated the effects of electron-phonon couplings, orbital degeneracies as well as randomness in detail, and clarified that all of these effects contribute to the colossal magnetoresistance through charge fluctuations.
2) We introduced the "Minimum model" as the most simplified effective model for dilute magnetic semiconductor system. We studied the thermodynamics of the model using CPA. It is found out a clear difference in the characteristic properties of the carrier-induced ferromagnetism between the model in the weak coupling regime and that in the strong coupling regime. In the weak coupling regime, ferromagnetism appears in the wide range of the carrier density n, while the Cu
… More
rie temperature Tc is kept low. In the strong coupling regime, however, ferromagnetic order is observed in a limited region of the carrier density n <x, where xis the impurity concentration, and Tcis maximum at n〜x/2.
3) We studied spinel oxides which exhibit strong electron correlations and geometrical frustrations. Concerning AV2_O_4 (A=Zn, Mg, Cd), we clarified the origin and the role of orbital degrees of freedom in the double phase transition and complex magnetic orders. For AV_2O_4 (A=Cd, Hg), we studied the gigantic half-magnetization plateau under magnetic field. The model not only explains the experimental results but also predicts various exotic phases such as quadropole ordered spin nematic phase. We also analyzed the structural phase transition in AIV2O4, and proposed the formation of the spin singlet state in the Heptamer cluster.
4) We studied the Hubbard model on the partial line graph lattice which exhibits flat bands. We investigated magnetisms due to strong correlations. As a result, we observed various magnetic phases such as partial ferromagnetism, ferrimagnetism and antiferromagnetism. Less
|
