Theoretical Study on multiband effect on the ferromagnetism of itinerant electrons
Project/Area Number  09640453 
Research Category 
GrantinAid for Scientific Research (C)

Section  一般 
Research Field 
物性一般(含基礎論)

Research Institution  University of Tsukuba 
Principal Investigator 
KUBO Kenn University of Tsukuba, Institute of Physics, Professor, 物理学系, 教授 (30015862)

CoInvestigator(Kenkyūbuntansha) 
MOMOI Tsutom University of Tsukuba, Institute of Physics, Research Associate, 物理学系, 助手 (80292499)

Project Fiscal Year 
1997 – 1998

Project Status 
Completed(Fiscal Year 1998)

Budget Amount *help 
¥2,100,000 (Direct Cost : ¥2,100,000)
Fiscal Year 1998 : ¥700,000 (Direct Cost : ¥700,000)
Fiscal Year 1997 : ¥1,400,000 (Direct Cost : ¥1,400,000)

Keywords  ferromagnetism / itinerant electrons / multipleband effect / Hurd's rule coupling / double exchange interaction / Collossal magnetoresistance / 強磁性 / 遍歴電子 / 多バンド効果 / フント結合 / 二重交換相互作用 / 巨大磁気抵抗効果 
Research Abstract 
1. We studied the 1D Hubbard model with twofold orbital degeneracy by using density matrix renormalization group method, and obtained ground state phase diagram. We obtained perfectly ferromagnetic ground state for n<1, n=1 and n>1 where n denotes the electron density per site. The ferromagnetism for n<1 was shown to be fragile against chay the band dispersion, while that for n>1 is robust. 2. We studied the doubly degenerate Habbard model in infinite dimensions by using the dynamical mean field theory, and to obtained ground stats place diagram. We obtained perfectly ferromagnetic ground state for n=1 and n>1 while we did not find ferromagnetic for n<1. We also found phase separation for n<similar or equal>1 and n<less than o From above results we established that the Hand's rule coupling which accompanies orbital degeneracy is quite effective in realizing ferromagnetism. Especially the socalled doubleexchange mechanism stabilizes metallic ferromagnetism for n>1. 3. We constructed a singlesite approximation for the single particle Green's function in the double exchange model. By using this Green's function are calculated the magnetic susceptibility and the electrical conductivity. 4. We obtained the ground state phase diagram of the double exchange model in infinite dimensions taking into account of full quantum effects of spins. 4.S=1/2のスピンを持つ二重交換模型の基底状態の相図を無限大次元単純立方格子において計算した。この結果強磁性、反強磁性、相分離の出現が確かめられた。また古典スピン系との比較により、スピンの揺らぎの量子効果が明らかになった。結果は現在投稿準備中である。

Report
(4results)
Research Output
(17results)