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

Allocation Type  Singleyear Grants 
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 Period (FY) 
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 
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.

Report
(3results)
Research Products
(17results)