期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：23
页码：7135-7140
DOI：10.1073/pnas.1422534112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceThere are certainly few remaining unsolved physics problems as simple and as fundamental as the magnetoelastic buckling phenomenon. In fact, it is just a little more complex than the Euler instability that describes the buckling transition of an axially compressed rod. Here, the bending energy is provided by the magnetization of the system and is balanced by the mechanical energy that hinders the deformation. It is fundamental in the respect that this mechanism could be realized at many different scales with many types of magnetic materials as soon as they offer the suitable combinations of parameters, mainly involving the magnetic susceptibility and the bending modulus. It could find many applications such as the magnetic remote control of nano- or microcantilevers. In its simplest form the magnetoelastic buckling instability refers to the sudden bending transition of an elastic rod experiencing a uniform induction field applied at a normal angle with respect to its long axis. This fundamental physics phenomenon was initially documented in 1968, and, surprisingly, despite many refinements, a gap has always remained between the observations and the theoretical expectations. Here, we first renew the theory with a simple model based on the assumption that the magnetization follows the rod axis as soon as it bends. We demonstrate that the magnetoelastic buckling corresponds to a classical Landau second-order transition. Our model yields a solution for the critical field as well as the shape of the deformed rods which we compare with experiments on flexible ferromagnetic nickel rods at the centimeter scale. We also report this instability at the micrometer scale with specially designed rods made of nanoparticles. We characterized our samples by determining all of the relevant parameters (radius, length, Young modulus, magnetic susceptibility) and, using these values, we found that the theory fits extremely well the experimental results for both systems without any adjustable parameter. The superparamagnetic feature of the microrods also highlights the fact that ferromagnetic systems break the symmetry before the buckling. We propose a magnetic "stick-slip" model to explain this peculiar feature, which was visible in past reports but never detailed.
关键词：magnetoelasticity ; buckling ; nanoparticles ; instability ; magnetic
