Messanae Universitas Studiorum

On generalizations of the snoek equation for magnetic relaxation phenomena

Restuccia, Liliana and Kluitenberg, Gerrit Alfred (1989) On generalizations of the snoek equation for magnetic relaxation phenomena. Accademia Peloritana dei Pericolanti Classe FF.MM.NN., 67. pp. 141-194.

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    Abstract

    In previous papers a thermodynamic theory for magnetic relaxation phenomena in continuous media was developed assuming that an axial vector field, which influences the magnetization, occurs as intemal thermodynamic degree of freedom. The Snoek equation for magnetic after effects was derived as a special case of this theory. In this paper it is assumed that several microscopic phenomena occur which give rise to magnetic relaxation and that it is possible to describe the contributions of these phenomena introducing in the expression for the entropy n «hidden» internal variables $Z^(^k^)$ (k = 1, 2,... , n) which are axial vectors and which influence the magnetic properties of the medium. With the aid of such vector fields $Z^(^k^)$, the specific total magnetization vector $m$ may be split in n+ 2 parts: $m^(0^)$, $m^(1^)$, $m^(2^)$, $m^(n^)$, $m^(n^+^1)$.
    The $n$ specific partial magnetization vectors $m^(^k^)$ (k = 1, 2, , n) may replace the $n$ internal variables $Z^(^k^)$ as thermodynamic internal degrees of freedom in the expression for the entropy. Using the general methods of non-equilibrium thermodynamics, the expression for the entropy production is derived, the phenomenological equations connected with irreversible changes in the magnetization, the generalized laws of Ohm, Fourier and Newton are formulated and the Onsager-Casimir relations for the phenomenological tensors are given. The results which are obtained are explicitly formulated in the case that the media under consideration are isotropic. A suitable form for the specific free energy $f$ is iritroduced to linearize the equations of state and in the case of anisotropic media the equations which govem the magnetic relaxation phenomena are obtained. Provided the phenomenological coefficients may be regarded as constants an explicit form for the magnetic relaxation equation in isotropic media is derived. This relaxation equation has the form of a linear relation among the magnetic field B, the first n derivatives with respect to time of this vector, the magnetization vector $M$ and the first $n + 1$ derivatives with respect to time of $M$.

    Item Type: Article
    Subjects: M.U.S. - Miscellanea > Atti Accademia Peloritana > Classe di Scienze Fisiche, Matematiche e Naturali > 1989
    M.U.S. - Miscellanea > Atti Accademia Peloritana > Classe di Scienze Medico-Biologiche > 1989
    M.U.S. - Miscellanea > Atti Accademia Peloritana > Classe di Scienze Giuridiche, Economiche e Politiche > 1989
    M.U.S. - Miscellanea > Atti Accademia Peloritana > Classe di Lettere, Filosofia e belle Arti > 1989
    Divisions: UNSPECIFIED
    Depositing User: Dr M P
    Date Deposited: 05 Oct 2012 09:21
    Last Modified: 22 Jan 2013 12:36
    URI: http://cab.unime.it/mus/id/eprint/932

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