1,720,987 research outputs found
The potentiality of composite elastic magnets as novel materials for sensors and actuators
No full textIn the last decade the progress of standard magneto-elastic materials is going toward its physical limits. New horizons are recently opened by the development of artificial composites having both elastic and magnetic properties. The working principle of these elastomagnetic materials is not depending on intrinsic magnetostriction, but on the coupling between magnetic moments of the particles and particles themselves. The possibility to study the physical mechanism that relates the elastic and magnetic properties in the new scenery furnished by composites of magnetic particles in an elastic matrix is very promising from the basic knowledge point of view. On the other side, the potential competitiveness in several applications justifies the increasing efforts to improve the production and to perform technical characterization of these magnetoelastic composites in different experimental conditions
Elastomagnetic effect in novel elastic magnets
No full textAn elastic and permanently magnetized material (Sm2Co7 particles uniformly dispersed in a silicone matrix) was produced. Bars of this material were put together to form samples with magnetic moment directions distributed as a fishbone. Results on the potentiality of this kind of material as both actuator and sensor, when a deformation is induced by an external magnetic field and when a magnetization change is induced by ail external dynamic deformation, respectively, are reported. (C) 2004 Elsevier B.V. All rights reserved
Magnetoelastic properties in amorphous ferromagnetic materials and potential applications
No full textLinearity of the direct elastomagnetic effect: evaluation and limits
No full textThe direct elastomagnetic effect in composite materials, made of ferromagnetic micro-magnets inside an elastomeric matrix, consists in their relative elastic deformation (10-4-10-3) under the action of an external magnetic field, dependent on the equilibrium between the magneto-mechanical moments and the internal elastic reaction, but independent of the standard magnetostriction. This investigation is focused on the evaluation of the strain linearity with the excitation field in view of the application of these materials for MEMS devices. The studied composite is made of permanently magnetized Sm2Co7 microparticles uniformly dispersed inside a silicone matrix. The field-induced strain is measured using a fiber Bragg grating sensor and, at the same time, theoretically evaluated from the model of the direct elastomagnetic effect. The linearity and reversibility of the material response are experimentally verified up to a threshold value of the magnetic field corresponding to the break in the coupling between the particles' magnetic moments and their body and to the passage from the linear magnetization to the non-linear regime accompanied by irreversible magnetization processes
A magnetoelastic amorphous ribbon in a silicone sheath as stress sensor and self indicator of strain threshold
No full textA magnetoelastic amorphous ribbon enveloped in silicone sheath has attenuated longitudinal magnetization intensity when is magnetized. At fixed magnetizing field, a longitudinal deformation applied to the silicone determines an ulterior decrease of magnetization intensity due to the induced friction at the interface between elastic sheath and ferromagnetic ribbon. When a threshold value of the silicone deformation is reached, an abrupt increase of magnetization occurs, corresponding to the exceeding of the maximum internal friction by the induced deformation. This effect can be used to design strain, stress, and/or magnetic field threshold indicators, which can be calibrated for different levels
Magnetoelastic properties in amorphous ferromagnetic materials and potential applications
No full textModeling of cantilever deflection for sensors and actuators: Role of Poisson's ratio for a unified theory
No full textWe construct a theory of the deflection of a bimorph cantilever, applicable to both the isotropic and anisotropic cases, and also including noise effects. The proposed formulation gives the correct expressions for the longitudinal and transverse deflections of a magnetoelastic cantilever for an arbitrary ratio of the thickness of the two components. The optimization of the cantilever as a sensor as a function of the thickness of the two components is discussed and also some results of the cantilever as an actuator are reported. (c) 2005 American Institute of Physics
Modified thermogravimetric apparatus to measure magnetic susceptibility on-line during annealing of metastable ferromagnetic materials
No full textThe insertion of proper coils to generate a magnetic field, with controlled gradient, in a standard thermogravimetric apparatus is shown to be a valid solution to measure on-line, upon heat treatment, the magnetic susceptibility in ribbon shaped samples of a metastable ferromagnetic material. The method is very useful to individuate the annealing conditions that optimise soft or hard magnetic properties without using separate apparatuses for heat treatment, control of the structural phase transition and characterization of magnetic susceptibility
Particle dimension effects on magnetization and strain sensitivity for a composite of nickel particles in silicone matrix
No full textSamples of composite material made of Ni ellipsoidal particles (with a fixed eccentricity but different major axis dimensions) uniformly dispersed in a silicone matrix were produced and characterized by both magnetization cycles and strain sensitivity of magnetization tests. It was theoretically justified and experimentally shown that at constant Ni percentage, in the case of nanometric size particles, higher coercive and saturation fields and a higher strain sensitivity of the magnetization intensity in comparison with the case of micrometric particles are obtained. (C) 2004 Elsevier B.V. All rights reserved
Magnetic Behaviour of Ni Nanoparticles Films Produced by Two Laser Irradiations in Vacuum
No full textMagnetic nanoparticles-assembled films are good candidates to obtain peculiar macroscopic magnetic properties which can be optimized for specific technological applications in a wide range of magnetomechanical and magnetoelectrical devices, by controlling the morphology and topology of the constituent nanoparticles (NPs). In fact, the physical properties of the systems of NPs associated to their small size and large surface-to-volume ratio can lead to peculiar properties that cannot be found in corresponding bulk materials. Despite the huge research efforts in the field of physical and chemical methods for the preparation of magnetic nanostructured systems - with reproducible narrow size distribution, controllable shape and proper NPs topology to tune suitable interplay between exchange and dipolar magnetic interactions - there is still a great need of simply, cost-effective synthesis techniques able to assure contemporaneously all the above mentioned characteristics. Femtosecond pulsed laser deposition (fs-PLD) in vacuum has been demonstrated to be a powerful and versatile tool for the production of metal and semiconductor nanoparticle-assembled films. In this work we study the possibility to modify the size and size distribution of the NPs produced by fs-PLD, by using the irradiation of the NPs plume with a secondary UV laser beam, and the consequent changes in the macroscopic magnetic behavior of the NP systems
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