Littérature scientifique sur le sujet « Cantilever Torque Magnetometry »

This PhD Thesis is the result of the work of the author as well as of many other collaborators. Since the field of molecular magnetism is a very specific interdisciplinary area that lies between solid state physics and chemistry, we decided to organize this Thesis starting with an Introduction (Chapter 2) that can help any reader to understand the main concepts that constitute the basis on which all the experiments and simulations performed here are grounded. Besides a brief history of magnetism (Section 2.1), we treated the modelling of magnetic anisotropy both in bulk (Section 2.2.1) and in molecular materials (Section 2.2.2), with a particular attention for molecular systems containing lanthanide ions. Indeed, the main purpose of this PhD Thesis is to study anisotropic systems, so we devoted a Chapter to explain the main sources of Non- collinearity (Chapter 3) in molecular materials, focusing on the ones arising from ligand geometry and crystal packing. The systems that are reported here were characterized using several techniques that are commonly used in molecular magnetism like EPR, AC and DC susceptometry, however the leading technique that was used for all the systems reported here is the Cantilever Torque Magnetometry (Chapter 4), that is treated in details both from a theoretical and from an experimental point of view, focusing on the type of measurements that can be performed and thus the physical quantities on which we can have information. A Section was also devoted to describe the basic program (that was modified ad hoc as a function of the studied system) that was written by the author with the assistance of Prof. Roberta Sessoli to fit and simulate the torque curves. The Chapters were organized in an increasing complexity fashion with four steps. From Collinear systems (Chapter 5), where all the anisot- ropy tensors are isooriented, we pass to Intermolecular noncollinear systems (Chapter 6), that contains more than one molecule that is not simply reported by an inversion centre. The next step was to study In- tramolecular noncollinear systems (Chapter 7), where the more than one anisotropic ion is present inside the molecule, thus adding a remarkable intricacy in the disentanglement of the single contributions. As a pioneer approach, we reported the investigation of Films of magnetic molecules on different substrates (Chapter 8), where the order is not in principle established, and could, up to now, being studied only using expensive techniques based on synchrotron light. Finally, we also included an Appendix where we attached all the articles already published by the Author and others on some results discussed in this Thesis.

Magneto-active elastomers (also called magnetorheological elastomers) are most often used in vibration attenuation application due to their ability to increase in shear modulus under a magnetic field. These shear-stiffening materials are generally comprised of soft-magnetic iron particles embedded in a rubbery elastomer matrix. More recently researchers have begun fabricating MAEs using hard-magnetic particles such as barium ferrite. Under the influence of uniform magnetic fields these hard-magnetic MAEs have shown large deformation bending behaviors resulting from magnetic torques acting on the distributed particles and consequently highlight their ability for use as remotely powered actuators. Using the magnetic-torque-driven hard-magnetic MAE materials and an unfilled silicone elastomer, this work develops novel composite geometries for actuation and locomotion. MAE materials are fabricated using 30% v/v 325 mesh barium ferrite particles in Dow Corning HS II silicone elastomers. MAE materials are cured in a 2T magnetic field to create magnetically aligned (anisotropic) materials as confirmed by vibrating sample magnetometry (VSM). Gelest optical encapsulant is used as the uniflled elastomer material. Mechanical actuation tests of cantilevers in bending and of accordion folding structures highlight the ability of the material to perform work in moderate, uniform fields of μ0H = 150 mT. Computational simulations are developed for comparison. Folding structures are also investigated as a means to produce untethered locomotion across a flat surface when subjected to an alternating field similar to scratch drive actuators; geometries investigated show promising results.