Phenomenological dynamics of XY spin glasses.
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We extend our previous (microscopic) study of the macroscopic dynamics of planar spin glasses to the case where the system has a remanent magnetization. In addition to employing, as macroscopic variables, the magnetization normal to the easy plane and the rotation angle about the axis normal to the easy plane, we utilize the result that random microscopic anisotropy which is bilinear in the spins leads to an in-plane macroscopic anisotropy with uniaxial symmetry. The present work is more phenomenological than the previous study, but as a consequence it is simpler to make predictions which are directly applicable to experiment. The zero-wave-vector mode, which involves the macroscopic variables identified above, is found to be field dependent when the static field is in the easy plane, so that it should be amenable to ESR measurements. (This mode can be described as a longitudinal mode, in the language of Heisenberg spin glasses.) As the measuring field is rotated in the plane, the resonance develops a complex angular dependence. This work also considers relaxation effects associated with the above macroscopic variables. Furthermore, since the in-plane macroscopic anisotropy is not fixed to the lattice, it is susceptible to change; we have, in addition, studied this slow anisotropy motion. 1986 The American Physical Society.
