Magnetic deformation of ferrogel bodies: Procrustes effect

Abstract

Deformation of spheroidal ferrogel bodies caused by a uniform magnetic field is investigated theoretically. The deformation is induced by two competitive mechanisms-magnetostatic and magnetostrictive. The former is due to the demagnetizing field of the sample and hence depends on its shape, while the latter originates from the magnetoelasticity of ferrogel and is shape independent. Both mechanisms are dipolar in nature and contribute-for a body of commensurate dimensions-oppositely to the effect. For an isotropic ferrogel sphere, the magnetostatic contribution still prevails and the magnetic field elongates the body. The two opposing mechanisms balance each other out for a prolate spheroidal sample with the axes aspect ratio a/b approximately 1.3 . It determines the so-called "Procrustes point" or "Procrustes size"-the magnetic field shrinks the body if a>1.3b and stretches it when a<1.3b .

Magnetodeformation of ferrogels and ferroelastomers. Effect of microstructure of the particles’ spatial disposition

“…[6][7][8], theoretically in Refs. [9][10][11][12][13][14][15], and by using computer simulations in Refs. [16][17][18][19].…”

“…Results of laboratory experiments and computer simulations, known from literature, very often contradict each other. Thus, contraction of the samples has been detected in the works [7,12,13,16], whereas elongation -in Refs. [8,19].…”

“…[13,15] shows that the type of the magnetodeformation is determined by competition of two mechanisms. The first one is the change of the sample demagnetizing factor, as a consequence of the sample deformation.…”

“…The second mechanism is the change of the sample magnetic susceptibility due to the change of the mutual disposition of the particles after the sample deformation. For single particles homogeneously distributed (like in a gas) in the matrix, the second mechanism stimulates contraction of the sample [13,15].…”

“…The work [13] deals with compositions of linearly magnetizable particles in a polymer matrix. This model is based on the estimates [21] of the ferrogel magnetic properties.…”