Enhanced differential magnetostrictive response in annealed Terfenol‐D

The field and pressure dependencies of the magnetostriction of Tb0.316Dy0.684Fe1.982 have been measured in a grain‐oriented rod after thermally annealing for 1 day at 850 °C and for 4 days at 950 °C in an argon atmosphere. The results of the heat treatment are a fivefold increase in the strain coefficient d 33(=dλ/dH) and a 100% increase in the maximum strain (λ). There was also an increase in the λ‐vs‐Hhysteresis. Under compressive uniaxial stress there was virtually no bulk change in magnetostrictive strain until the field exceeded a critical value which depended on the applied stress, for instance ∼12 kA/m under a stress of 6 MPa

Enhancement of piezomagnetic response of highly magnetostrictive rare earth‐iron alloys at kHz frequencies

The effects of Al and Si additions on the frequency response of highly magnetostrictive Tb–Dy–Fe alloys have been studied. These elements reduced the electrical conductivity of the material, thereby increasing the depth of penetration of acmagnetic fields and extending the operational frequency range. Complex permeability measurements were made on doped and undoped polycrystalline samples with the objective of studying the improvement in energy conversion efficiency at kilohertz frequencies as a result of the alloying additions. The resulting complex permeability was compared with the values for single crystal specimens of Tb0.3Dy0.7Fe1.92 at a range of frequencies from 10 Hz to 50 kHz

Mechanism, dynamics, and biological existence of multistability in a large class of bursting neurons

Multistability, the coexistence of multiple attractors in a dynamical system, is explored in bursting nerve cells. A modeling study is performed to show that a large class of bursting systems, as defined by a shared topology when represented as dynamical systems, is inherently suited to support multistability. We derive the bifurcation structure and parametric trends leading to multistability in these systems. Evidence for the existence of multirhythmic behavior in neurons of the aquatic mollusc Aplysia californica that is consistent with our proposed mechanism is presented. Although these experimental results are preliminary, they indicate that single neurons may be capable of dynamically storing information for longer time scales than typically attributed to nonsynaptic mechanisms.Comment: 24 pages, 8 figure

Dependence of energy dissipation on annealing temperature of melt–spun NdFeB permanent magnet materials

A model of magnetic hysteresis which was developed originally for soft magnetic materials has been applied to melt–spun ribbons of Nd2Fe14B‐based material. The crucial ideas in the model description of hysteresis center on a dissipation of energy due to hysteresis which is proportional to the change in magnetization. The Nd2Fe14B material was melt–spun amorphous and then annealed for a period of 24 h at temperatures ranging from 700 to 950 °C. This resulted in different grain sizes, depending on annealing temperature. Consequently the hysteresis curves represent the properties of the material as a function of both annealing temperature and grain size. It was found that the magnetic properties varied systematically with annealing temperature, and hence grain size, as would be expected. When modeling the magnetic properties it was found that the model parameters also varied systematically, in particular, the energy dissipation parameter k was to a first approximation a simple linear function of the annealing temperature and decreased with increasing annealing temperature as a result of grain growth. Therefore, this study revealed a basic relationship between materials processing conditions, microstructure, model parameters, and magnetic properties

Structural and magnetic properties of Ti4+/Co2+ co-substituted cobalt ferrite

The variations in the structural magnetic properties of cobalt ferrite due to Ti4+/Co2+ co-substitution for 2Fe3+ are presented. The non-linear relation in the variation of the lattice parameter agrees with a previous study on cation distribution, which showed that the rate of substitution of cations into the A-sites and B-sites varies with Ti-concentration. Such variation in the rate of substitution into the cation sites was also observed in the magnetization, coercive field, and susceptibility data. The coercive field and differential susceptibility are inversely related. Although the coercive field of the Ti-substituted cobalt ferrite generally decreased compared to the un-substituted cobalt ferrite, magnetic susceptibility was higher at higher Ti-concentrations

Temperature dependence of the magnetomechanical effect in metal-bonded cobalt ferrite composites under torsional strain

Metal-bonded cobaltferrite composites are promising candidates for torquesensors and other magnetostrictive sensing and actuating applications. In the present study, the temperature dependence of the magnetomechanical effect in a ring-shape cobaltferrite composite under torsional strain has been investigated in the temperature range of −37 to 90 °C. The changes of external axial magnetic field were measured as a function of applied torque. Magnetomechanical sensitivity of ΔHext/Δτ=65 A N−1 m−2 was observed with a magnetomechanical hysteresis of Δτ=±0.62 N m at room temperature (22 °C). These were then measured as a function of temperature. Both decreased as the temperature increased throughout the entire range. The magnetomechanical hysteresis became negligible at temperatures higher than 60 °C, above which there was a linear change in external magnetic field with applied torque. These temperature dependences are explained by the changes of magnetostriction, anisotropy, spontaneous magnetization, and pinning of domain walls caused by the availability of increased thermal energy

Material for magnetostrictive sensors and other applications based on ferrite materials

The present invention provides magnetostrictive compositions that include an oxide ferrite which provides mechanical properties that make the magnetostrictive compositions effective for use as sensors and actuators

Magnetic Property Changes in various Structural Steels Due to Irradiation

Nondestructive evaluation in nuclear power plants has been a growing concern for electric utility operators over the past decade 1. Many plants are operating beyond their original design lives primarily through intermittent replacement of individual components as necessary. It is critically important for the NDE field to develop technology that can evaluate the life expectancy of components in these plants, such as steam boiler pipes, headers and tubes, steam turbine rotors and blades, and nuclear pressure vessels. These components typically experience long service exposure, high temperature under high loading conditions, corrosive media and neutron irradiation. The focus of this paper will be on the irradiation effects

Effect of anatomical variability in brain on transcranial magnetic stimulation treatment

Transcranial Magnetic Stimulation is a non-invasive clinical therapy used to treat depression and migraine, and shows further promise as treatment for Parkinson’s disease, Alzheimer’s disease, and other neurological disorders. However, it is yet unclear as to how anatomical differences may affect stimulation from this treatment. We use finite element analysis to model and analyze the results of Transcranial Magnetic Stimulation in various head models.A number of heterogeneous head models have been developed using MRI data of real patients, including healthy individuals as well as patients of Parkinson’s disease. Simulations of Transcranial Magnetic Stimulation performed on 22 anatomically different models highlight the differences in induced stimulation. A standard Figure of 8 coil is used with frequency 2.5 kHz, placed 5 mm above the head. We compare cortical stimulation, volume of brain tissue stimulated, specificity, and maximum E-field induced in the brain for models ranging from ages 20 to 60. Results show that stimulation varies drastically between patients of the same age and health status depending upon brain-scalp distance, which is not necessarily a linear progression with age

Effect of the elastic modulus of the matrix on magnetostrictive strain in composites

The effect of the matrix material on the magnetostriction of composites containing highly magnetostrictive particles has been studied. Experimental results showed that the elastic modulus of the matrix is an important factor determining the bulk magnetostriction of the composite. For a series of composites with the same volume fraction of magnetostrictive particles but different matrix materials, the bulk magnetostriction was found to increase systematically with decreasing elastic modulus of the matrix. A modeltheory for the magnetostriction of such composites has been developed, based on two limiting assumptions: uniform strain or uniform stress inside the composite. The theory was then used to predict the magnetostriction of the entire material from the volume fractions of the components, their elastic moduli and magnetostrictions. These predictions were in agreement with the experimental results. It is concluded that to obtain a high magnetostriction and adequate mechanical properties of a composite, the elastic moduli of the magnetostrictive phase and the matrix should be as close as possible in value