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Excitations and Phase Transitions of Disordered Magnetic Systems

  • R. A. Cowley
Part of the Ettore Majorana International Science Series book series (EMISS, volume 46)

Abstract

Randomly mixed transition metal fluorides are ideal systems with which to study the excitations and phase transitions of disordered systems. The crystal structures and magnetic interactions are well known and relatively simple, while different materials are magnetically two-or three-dimensional and have effectively Ising or Heisenberg interactions. The excitations of several of these mixed systems have been studied and the results show the importance of the Ising cluster modes. The results are consistent with computer simulations, but the coherent potential approximation does not describe the results in detail. The usefulness of fractons as a description of the results is still not established. The phase transitions of systems with well defined magnetic ground states are now well understood both experimentally and theoretically. The results for d = 2 and 3 Ising models are described. Close to the percolation point, a multicritical model based on geometric and thermal disorder and the importance of one-dimensional weak links describes the results for concentrations less than the percolation concentration. There are a number of unexplained results for concentrations above percolation. Random fields have a dramatic effect on the structure and phase transitions of magnetic systems. Experiments to investigate the resulting metastability and possible phase transitions are described, but the results are still not understood in detail.

Keywords

Ising Model Range Order Spin Wave Magnetic Excitation Coherent Potential Approximation 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Plenum Press, New York 1989

Authors and Affiliations

  • R. A. Cowley
    • 1
  1. 1.Department of PhysicsUniversity of EdinburghEdinburghScotland, UK

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