ISSN:
1089-7550
Source:
AIP Digital Archive
Topics:
Physics
Notes:
The magnetoelastic effects are usually described on the basis of an expression for the magnetoelastic energy which is a function of the symmetric strain εij and of the magnetization direction cosines αi and which has the form Eme=Bijkeεijαkαl, the number of different Bijkl being limited by symmetry. This expression, however, does not satisfy the principle of rotational invariance, i.e., the coupling energy varies when the reference system is rotated; this is equivalent to saying that it does not properly describe the effects of an applied strain containing an antisymmetric component ωij. This problem was previously recognized, studied for special cases, and related effects were observed. However, to our best knowledge, no explicit calculation of rotationally invariant magnetoelastic energy has been previously reported for the general cases of cubic and uniaxial symmetry. We will simply derive these expressions starting from an expansion of the energy of a magnetoelastic system in terms of the particles displacement gradients uij, using the definitions of the symmetric and antisymmetric strain tensors (εij=uij+uji; wij=uij−uji) andimposing the rotational invariance. It results that, at the lowest order, the rotational invariant expression for the magnetoelastic energy has the form: Eme=Bijklεijαkαl +Pijklwijαkαl +Qijkl(αm)wijεkl +Rijkl(αm)wijwkl; explicit expressions for Pijkl, Qijkl(αm), and Rijkl(αm) will be given for the cases of uniaxial and cubic symmetry. Finally it will be shown how, using a simple transformation, the known theory on the elastic properties of magnetoelastic materials can be used for applied strains having antisymmetric components.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.338652
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