THEORY OF DYNAMICAL BEHAVIORS OF FERROMAGNETIC SPINS
Journal Article
·
· Progr. Theoret. Phys. (Kyoto)
The dynamical behavior of ferromagnetic spins is studied from statistical mechanics of irreversible processes. A macroscopic equation determining the change in time of an inhomogeneous magnetization is derived giving explicit expressions for the frequency spectrum and damping constant. Using the general expressions, the pair correlation of spins, the magnetic scattering cross section of neutrons, the frequency spectrum and the damping constant of spin waves, and the damping of the longitudinal spin component above and below the Curre point are discussed on the basis of the Heisenberg model of ferromagnetic spins. In the low temperature limit, a straightforward reduction of the expressions leads to the spin wave frequency and damping equivalent to Dyson' s theory or spin wave interactions. A general expression is given for van Hove's parameters de scribrng the asymptotic behavior of the spin pair correlation at large distances. The longitudinal spin damping in the low- temperature limit exhibits k dependences, depending upon the relative magnitudes of the spin wave energy Dk/sub 2/, the effective magnetic freld H coming from other than the exchange interaction and the thermal energy k /sub B/T; in particular, for g mu /sub B/H << Dk/sup 2/ << k/sub B/T, the longitudinal damping is proportional to k/sup 2/, namely, the change in time of the longitudinal spin density obeys the diffusion equation. Near the Curie point and in the paramagnetic region, the longitudinal damping obeys the diffusion equation. The diffusion constant vanishes at the Curie point and agrees with values for iron above the Curie point. (auth)
- Research Organization:
- Kyoto Univ.
- Sponsoring Organization:
- USDOE
- NSA Number:
- NSA-16-026013
- OSTI ID:
- 4825783
- Journal Information:
- Progr. Theoret. Phys. (Kyoto), Journal Name: Progr. Theoret. Phys. (Kyoto) Vol. Vol: 27
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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