1993 Fiscal Year Final Research Report Summary
Chaos and Multi-Fractal in Nonlinear Spin Dynamics
| Project/Area Number |
02402009
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| Research Category |
Grant-in-Aid for General Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Research Field |
固体物性
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| Research Institution | Okayama University |
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Principal Investigator |
YAMAZAKI Hitoshi Okayama University, Faculty of Science Professor, 理学部, 教授 (40013495)
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| Co-Investigator(Kenkyū-buntansha) |
MARUYAMA Hiroshi Okayama University, Faculty of Science Associate Professor, 理学部, 助教授 (20181836)
TANAKA Motoyuki Okayama University, Faculty of Science Professor, 理学部, 教授 (80032803)
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| Project Period (FY) |
1990 – 1993
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| Keywords | Chaos / Fractal / Spin-waves / Magnon / Parametric excitation / Parallel pumping / Spin-wave turbulence |
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| Research Abstract |
A spin-wave system under parametric excitation provides a good example of nonlinear and nonequilibrium spin dynamics system. Spin-wave pairs grow far above the thermal levels under parametric excitation ehich is performed by parallel and perpendicular pumping When microwave power is increased well above the threshold of Suhl instability, the system becomes unstable and the number of spin-wave varies with time. Many types of regular and irregular auto-oscillations are observed, that is, period-doubling bifurcation, qeasi-periodic and intermittency chaos. Since magnetism is well understood by microsscopic quantum theory, it is one of excellent examples of theoretical research of chaos.
Fractal dimensions, return maps, Lyapunov exponents, strange attractor and f(alpha) spectra are studied as a function of magnetic field and driving microwave power. f(alpha) spectra, which characterize the multi-fractal structure of chaotic strange attractor, observed at the onset of chaos (critical regime)are in excellent agreement with the theoretical universal spectra of period-doubling route to chaos. The spectra observed in chaotic regime is different from one in critical regime and both spectra of critical and chaotic regimes are observed in the crossover region. Numerical simulation by microscopic model Hamiltonian gives similar bifurcation phenomena of f(alpha) spectra.
Transition from quasiperiodicity to chaos through a torus and phase locking is observed. Intermittency chaos observed just above the onset of auto-oscillations was studied by Poincare maps and distribution of laminar period lengths. Arnold's tongue and frequency-locked state are observed under modulated pumping field Nonlinear radiation damping of parametrically excited spin-waves are theoretically and experimentally studied.
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