Rev. Phys. Appl. (Paris)
Volume 5, Numéro 1, février 1970
Page(s) 77 - 82
Rev. Phys. Appl. (Paris) 5, 77-82 (1970)
DOI: 10.1051/rphysap:019700050107700

Theoretical aspects of magnetic fluctuations

Ronald E. Burgess

Department of Physics, University of British Columbia, Vancouver 8, B.C., Canada

The thermodynamic treatment of equilibrium fluctuations in magnetic systems is discussed and applied to a variety of situations. The spectral density of the magnetic moment or flux are derived for simply-connected bodies (sphere and cylinder) and for multiply-connected systems (loop and hollow cylinder). The material is considered to be either a normal conductor, a superconductor or ferromagnetic. The results are valid in the presence of a static magnetic field and also if the susceptibility is field-dependent. No abrupt change in fluctuations occurs as a superconductor is taken through the transition temperature. The introduction of a Josephson junction or a resistive link in a superconducting loop is shown to increase the flux fluctuations markedly with a steady increase as the link is made weaker. At high frequencies the fluctuation spectrum for a superconductor approaches that for the same system in the normal state.

0755 - Magnetic instruments and techniques.

Key words
fluctuations -- magnets -- thermodynamic applications