Critical Magnetic Relaxation : Quasi-Collective Mode and Dynamic Scaling

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Connected with neutron inelastic scattering in a magnetic system, a number of deviations from the results of a conventional kinetic theory have been suggested and observed. Among others the possibility of observing quasi-collective modes (or "sloppy spinwaves") in the paramagnetic phase, and the exact power index of critical singularity exhibited in dynamic characteristics (i.e. "the dynamic scaling") may be counted as typical examples. In this paper these problems are discussed on the basis of canonical correlation function. It is pointed out that in the neighbourhood of the transition the part of the correlation function which deviates from a linear stochastic theory becomes increasingly important in its contribution to the neutron scattering spectrum. In particular, the importance of the dynamic imbalance, i.e. of the torque spectrum, has been demonstrated on the basis of a dynamic theory, though admittedly approximate. For an arbitrary value of wave number k a closed form for the canonical correlation spectrum was obtained. Two main features emerged from the computation, i.e. (1) the existence of sloppy spinwaves for k>κ, and (2) proper scaling properties for k<1/2. These results have also provided a good understanding of the existing neutron inelastic scattering data in magnetic substance (e.g. RbMnF_3), including agreements in numerical magnitude. It is found that the validity of the conventional theory is assured for k>κ.
理論物理学刊行会の論文
1971-01-25

Critical Magnetic Relaxation : Quasi-Collective Mode and Dynamic Scaling

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