1999 Fiscal Year Final Research Report Summary
Magnetism of Site Random Model - Coexistence of Ferromagnetism and Antiferromagnetism -
| Project/Area Number |
09640452
|
|---|
| Research Category |
Grant-in-Aid for Scientific Research (C)
|
| Allocation Type | Single-year Grants |
|---|
| Section | 一般 |
|---|
| Research Field |
物性一般(含基礎論)
|
|---|
| Research Institution | TOHOKU UNIVERSITY |
|---|
Principal Investigator |
MATSUBARA Fumitaka Graduate School of Engineering, Tohoku University, Professor, 大学院・工学研究科, 教授 (90124627)
|
|---|
| Co-Investigator(Kenkyū-buntansha) |
SHIRAKURA Takayuki Humanity and Social Science, Iwate University, Associate Professor, 人文社会科学部, 助教授 (90187534)
SUZUKI Nobuo Graduate School of Engineering, Tohoku University, Research Assistant, 大学院・工学研究科, 助手 (30302186)
NAKAMURA Tohta Graduate School of Engineering, Tohoku University, Research Assistant, 大学院・工学研究科, 助手 (50280871)
|
|---|
| Project Period (FY) |
1997 – 1999
|
| Keywords | Site-Random / Spin-Glass / Mesoscopic Magnetic Films / Dipole Interaction / Monte Carlo / Cluster Heat Bath |
|---|
| Research Abstract |
1. Low Temperature Phase of Spin Glasses
We have proposed a new method for evaluating the defect energy of spin glass models on finite lattices. Using the method, we have reexamined the stability of the spin glass phase of two models, the Ising model in two dimensions and the Heisenberg model in three dimensions. For both the models, the defect energy increases with the size of the lattice, suggesting the occurrence of a finite temperature phase transition. These results disprove the previous idea that the spin glass phase is realized only in the Ising model in three dimensions.
2. New Simulation Algorithm
We have developed two simulation methods, a cluster heat bath (CHB) method and a discrete update Monte Carlo method. The former method is a hybridized one of an analytic method and a stochastic method, and very effective for studying complex systems. The latter method is one for systems with long-range interactions and used for studying the spin structure of mesoscopic systems.
3. Spin Structure of Mesoscopic Ultrathin Magnetic Films
We have studied magnetic properties of micron- and submicron-scale ultrathin ferromagnetic films with uniaxial anisotropy using a discrete update Monte Carlo method. We have found that those films exhibits different magnetic properties depending on their lattice size. In small lattices, the films exhibit properties similar to those of a usual ferromagnet. In moderate lattices, the specific heat exhibits a double peak and the magnetization increases abruptly around the lower peak temperature. In large lattices, the magnetization does not increase but the specific heat still exhibits a double peak.
|
