2006 Fiscal Year Final Research Report Summary
Magnetic Dipolar Interactions and Reentrant Spin-Glass Transition
| Project/Area Number |
16540335
|
|---|
| Research Category |
Grant-in-Aid for Scientific Research (C)
|
| Allocation Type | Single-year Grants |
|---|
| Section | 一般 |
|---|
| Research Field |
Mathematical physics/Fundamental condensed matter physics
|
|---|
| Research Institution | Tohoku University |
|---|
Principal Investigator |
MATSUBARA Fumitaka Tohoku University, Graduate School of Engineering, Professor, 大学院工学研究科, 教授 (90124627)
|
|---|
| Co-Investigator(Kenkyū-buntansha) |
SHIRAKURA Takayuki Iwate University, Humanity and Social Science, Professor, 人文社会科学部, 教授 (90187534)
SUZUKI Nobuo Tohoku Bunka Gakuen University, Science and Technology, Lecturer, 科学技術学部, 講師 (30302186)
|
|---|
| Project Period (FY) |
2004 – 2006
|
| Keywords | Spin-Glass / Reentrant Spin-Glass / Dilute Ferromagnet / Monte Carlo Simulation / Genetic Algorism |
|---|
| Research Abstract |
Reentrant spin-glass (RSG) transition is a well-known phenomenon of spin glasses (SGs). However, the mechanism responsible for the RSG transition has not yet been resolved. In this project, we found for the first time a realistic model which reproduces the RSG phenomena and studied the mechanism responsible to the RSG transition.
1. RSG Model
We considered the magnetic ordering of a dilute ferromagnetic (FM) Heisenberg model AxBi-x (0<x<l) with antiferromagnetic next-nearest neighbor interactions, where A is a ferromagnetic atom and B a non-magnetic atom. We performed a large scale Monte Carlo simulation of the model with x~0.8 on various sizes of the LXLXL lattice and found that the model reproduces the RSG transition. That is, as the temperature is decreased, the magnetization increases rapidly below a certain temperature, reaches a maximum value, then ceases at some lower temperature. The low temperature phase was suggested to be a SG phase that is characterized by ferromagnetic clust
… More
ers. Then having performed the same simulation for various x, we determined a "concentration(x)-temperature(7) phase diagram"of the model. We applied the model to study the phase diagram of EuxSri-xS, which is an experimental realization of the model.
2. RSG Transition and Fluctuating Clusters
We examined the RSG transition in the dilute FM model. We calculated the site magnetization having developed a novel simulation algorism that removes uniform rotation of the spins. Results showed that clusters of fluctuating spins exist in the FM phase. As the temperature is decreased, the spins in those clusters freeze and the FM long-range order breaks to ferromagnetic clusters. These results are compatible with experimental observations. The fluctuating clusters appear in domains with lower spin concentrations. Hence we suggested that the RSG transition comes from a scattering of local concentration of the magnetic atoms.
3. Genetic Algorism for Heisenberg Models
We developed a genetic algorism for Heisenberg model having generalized Pal's genetic algorism for the Ising SG. The algorism was used to analyze the ground state properties of the dilute model. Less
|
Research Products
(20 results)
