Magnetoelastic Stress Research Articles

Application of magnetoelastic stress sensors in large steel cables

In this paper, the application of magnetoelasticity in static tension monitoring for large steel cables is discussed. Magnetoelastic (EM) stress sensors make contact-free tension monitoring possible for hanger cables and post-tensioned cables on suspension and cable-stayed bridges. By quantifying the correlation of magnetic relative permeability with tension and temperature, the EM sensors inspect the load levels in the steel cables. Cable tension monitoring on Qiangjiang (QJ) 4th Bridge demonstrates the reliability of the EM sensors.

The dynamic response and perturbation of magnetic field vector of orthotropic cylinders under various shock loads

In this paper, an analytical method is introduced to solve the problem for the dynamic stress-focusing and centred-effect of perturbation of the magnetic field vector in orthotropic cylinders under thermal and mechanical shock loads. Analytical expressions for the dynamic stresses and the perturbation of the magnetic field vector are obtained by means of finite Hankel transforms and Laplace transforms. The response histories of dynamic stresses and the perturbation of the field vector are also obtained. In practical examples, the dynamic focusing effect on both magnetoelastic stress and perturbation of the axial magnetic field vector in an orthotropic cylinder subjected to various shock loads is presented and discussed.

Nanomechanical Measurement of Magnetostriction and Magnetic Anisotropy in (Ga,Mn)As

A GaMnAs nanoelectromechanical resonator is used to obtain the first measurement of magnetostriction in a dilute magnetic semiconductor. Resonance frequency shifts induced by field-dependent magnetoelastic stress are used to simultaneously map the magnetostriction and magnetic anisotropy constants over a wide range of temperatures. Owing to the central role of carriers in controlling ferromagnetic interactions in this material, the results appear to provide insight into a unique form of magnetoelastic behavior mediated by holes.

On multiple circular inclusions in plane magnetoelasticity

A general series solution to the magnetoelastic problem of interacting circular inclusions in plane magnetoelasticity is provided in this paper. By the use of complex variable theory and Laurent series expansion method, the general expression of the magnetic and the magnetoelastic complex potentials for the circular inclusion problem is derived. Expanding the definition of the Airy’s stress function of pure elastic field into the magnetoelastic field and applying the superposition method, the general expression then can be reduced to a set of linear algebraic equations and solved in a series form. An approximate closed form solution for the case of two arbitrarily located inclusions is also provided. For illustrating the effect of the pertinent parameters, the numerical results of the interfacial magnetoelastic stresses are displayed in graphic form.

Stress–strain state of a piecewise homogeneous ferromagnetic body with an interfacial penny-shaped crack

This paper considers the stress–strain state of a body consisting of two bonded uniform ferromagnetic half-spaces, with an interfacial penny-shaped crack. The body is assumed to be acted on by a uniform magnetic field in a direction normal to the crack and interface. The problem is reduced to the solution of singular integral equations with respect to two unknown functions on a finite interval. These functions are defined analytically, allowing us to obtain formulae for the magnetoelastic stresses and coefficient of stress intensity. From these formulae, the influence of various physico-mechanical parameters and the magnetic field on the stress strain state of the body in the vicinity of crack is studied.

Manganese-substituted cobalt ferrite magnetostrictive materials for magnetic stress sensor applications

Metal bonded cobalt ferrite composites have been shown to be promising candidate materials for use in magnetoelastic stress sensors, due to their large magnetostriction and high sensitivity of magnetization to stress. However previous results have shown that below 60°C the cobalt ferrite material exhibits substantial magnetomechanical hysteresis. In the current study, measurements indicate that substituting Mn for some of the Fe in the cobalt ferrite can lower the Curie temperature of the material while maintaining a suitable magnetostriction for stress sensing applications. These results demonstrate the possibility of optimizing the magnetomechanical hysteresis of cobalt ferrite-based composites for stress sensor applications, through control of the Curie temperature.

Magnetostriction in thin films of manganites and cobaltites

Comparison of the magnetostriction effects in manganite and cobaltite thin films has been presented. The detailed analysis of the magnetostriction effects has been performed for epitaxial thin films with the same level of doping, namely on the La0.67Ca0.33MnO3 and La0.7Sr0.3CoO3 films grown using laser deposition on twins free substrates. The magnetoelastic stress was measured using capacitance cantilever technique in wide temperature range 4.2–300 K. It was shown that magnetostriction of manganite films is typical in value for ferromagnetic 3d metals. From the temperature dependence of the magnetostriction constant it may be concluded that the single ion mechanism dominates in this type of films. In the case of cobaltite films two mechanisms give significant contribution to the magnetostriction effects: a magnetic field induced increase of the volume of ferromagnetic clusters and magnetic field induced spin state transitions. The first mechanism dominates at high temperatures. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The influence of thermal treatment on the properties of Co‐based magnetoelastic sensing elements

Cobalt-based amorphous alloys (such us Co68Fe4B13Si13.5Mo1.5) may be utilized in cores of magnetoelastic stress and force sensors. To achieve the proper functional parameters of core's material, the proper heat treatment should be applied. Paper presents results of the magnetoelastic investigation carried out on two ring samples. First sample was as quenched and second sample was annealed at temperature of 360 oC for 1 hour. The compressive stress was applied to the ring core perpendicularly to the flux density direction. The changes of the magnetic properties of both samples, as a function of compressive stresses, are presented. High stress sensitivity of both samples was observed in spite of a low magnetostriction of Co68Fe4B13Si13.5Mo1.5 amorphous alloy. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Solutions for curvilinear cracks in bonded dissimilar materials subject to uniform magnetic induction

The magnetoelastic problem of curvilinear cracks lying along the interface between two dissimilar ferromagnetic materials under remote uniform magnetic induction is considered. On the basis of the Hilbert formulation and a special technique of analytical continuation, the solutions of the magnetic and the magnetoelastic stress fields either in the matrix or in the inclusion are expressed in a general form. Just like the pure elastic problem of curved cracks or the magnetoelastic problem of straight cracks in bonded dissimilar media, the trig-log character for the singularity of magnetoelastic stresses is found in this paper. Both the explicit solutions and the numerical results for the illustrating case of a single circular-arc crack in bi-material plate with typical ferromagnetic materials are given to elucidate the use of the present study. It is noted that the stress intensity factors are obtained and verified by comparison with the existing ones under special cases. The validity of the crack opening condition is also discussed.

Perpendicular magnetic fields in cantilever beam magnetometry

Cantilever beam magnetometry is a common technique to determine the magnetoelastic (ME) coupling constants of thin films by measuring the stress that develops when the film magnetization is changed. In cantilever beam experiments performed so far the film magnetization was mainly rotated within the film plane. Here we discuss the measurement of the ME coupling constants, when the magnetizing field is chosen so that it rotates the film magnetization out of the film plane. A major stress contribution, which arises additionally to the ME stress, originates in the torque that magnetic dipoles experience in a magnetic field. In order to separate torque effects from ME contributions in cantilever beam experiments a general method is proposed. With this method the ME coupling constants can be quantitatively determined and furthermore the film magnetization as well as its perpendicular anisotropy constant are obtained quantitatively.

Magnetoelastic stress inCu∕Ni∕Cu∕Si(100)epitaxial thin films

The magnetoelastic (ME) stresses for a series of $\mathrm{Cu}∕\mathrm{Ni}({t}_{\mathrm{Ni}})∕\mathrm{Cu}∕\mathrm{Si}(001)$ epitaxial films are reported. The direct measurement of the stresses in the (001) plane allows determination of the irreducible ME stress ${B}_{\mathrm{eff}}^{\ensuremath{\gamma},2}$ that accounts for the breaking of the in-plane square symmetry. ${B}_{\mathrm{eff}}^{\ensuremath{\gamma},2}$ has been determined as a function of the applied magnetic field $(\ifmmode\pm\else\textpm\fi{}15\phantom{\rule{0.3em}{0ex}}\mathrm{kOe})$ and the temperature $(300--10\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ for ${t}_{\mathrm{Ni}}$ ranging from 5 to $15\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. The temperature dependence of ${B}_{\mathrm{eff}}^{\ensuremath{\gamma},2}$ is proportional to the square power of the reduced magnetization and the $0\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ value increases with the internal stress. These experimental observations are explained considering the tetragonal distortion of the nickel caused by the epitaxial strain that the copper lattice introduces in the nickel layers.

Magnetocrystalline anisotropy in a(110) (Tb0.27Dy0.73)Fe2 thin-film

Magnetic anisotropy measurements performed in a (110)(Tb0.27Dy0.73)Fe2 (Terfenol-D) film epitaxially grown on a sapphire substrate are presented. The magnetictorque curves have been determined by using a vectorial vibrating sample magnetometer,which allows us to measure the angular dependence of magnetization components parallel,, and perpendicular, , to the applied field up to 2 T. The fourfold symmetry associated with thecubic structure within the (110) plane is clearly observed. The analysis ofthe experimental torque has been carried out considering magnetocrystallineanisotropy up to sixth order and magnetoelastic energy up to second order; so,the magnetocrystalline anisotropy constants in the (110) plane of the film,K1 and K2, have been obtained. This allows us to determine the direction of the magnetization easyaxis for (110) Terfenol-D thin-film: it is at RT, passes through at 140 K and then changes to at 40 K. It was completely impossible to explain the angular dependence of the experimentalmagnetic torque without including shear and tetragonal magnetoelastic stress parameters,b2 and b1, respectively. This confirms the paramount role of the strain in the determination of themagnetic properties in this kind of Terfenol-D thin film.

The possibility of utilizing the high permeability magnetic materials in construction of magnetoelastic stress and force sensors

The paper presents new possibilities in the field of construction of the magnetoelastic stress and force sensors. Two methods of applying mechanical stress to the core of the magnetoelastic sensing elements were presented. The first one is suitable for bulk magnetic materials, such as ferrites. The second method can be utilized in a case of both ribbon and bulk ring cores. Such ring-shaped cores can be made of amorphous alloys as well as ferrites. Both these methods enable achieving uniform distribution of stresses in the samples with closed magnetic circuit. The experiment was performed on high permeability Mn–Zn ferrite and Co-rich amorphous alloy. The results confirm, that magnetic properties of both ferrite and amorphous alloys change significantly under compressive stress from the external forces. The relative changes of the permeability exceed 100% for stresses up to 25 MPa. Paper presents also functional characteristics of the magnetoelastic sensor which operate in the resonant circuit configuration. Output frequency signal from the sensor operating in this configuration is suitable for further digital processing.

Epitaxial strain and interface effects on the magnetoelastic behaviour of Dy/Ho and Dy/Lu superlattices

Abstract The basal plane magnetoelastic stress, B γ ,2 , of Dy 16 /Ho 22 , Dy 14 /Lu 30 and Dy 21 /Lu 11 (0 0 0 1) superlattices is investigated. For Dy 16 /Ho 22 we obtain B γ ,2 (12 T, 0 K)=0.4 GPa, while for Dy 14 /Lu 30 and Dy 21 /Lu 11 it amounts 0.33 and 0.9 GPa, respectively. In the first case, the value obtained is explained in terms of the known values of B γ ,2 for bulk Dy and Ho, including small interface and strain contributions, whereas in the Dy/Lu samples, B γ ,2 have large non-bulk contributions. The differences in epitaxial compression and in electronic structure for both kind of superlattices can explain these results.

Measuring the magnetoelastic anisotropy constant in manganite epitaxial thin films

Abstract We present direct measurement and indirect determination of the irreducible magnetoelastic stress coefficient B1 performed in La2/3Ca1/3MnO3 epitaxial thin films grown on SrTiO3(0 0 1) and LaAlO3(0 0 1) substrates. The values obtained are, respectively, −13 and −16 MPa. These results suggest the magnetoelastic origin of the magnetic anisotropy energy that induces out-of-plane magnetization in La2/3Ca1/3MnO3/LaAlO3 (0 0 1) thin films.

Magnetoelasticity in dysprosium–scandium superlattices

Abstract We have studied the magnetoelastic stress parameter, B γ ,2 , associated with the shear deformation within the basal plane of the (0 0 0 1) Dy (20 A)/Sc ( t =20–60 A) superlattices (SLs). The extrapolated B γ ,2 (0 K) values change from 1.45 to 0.9 GPa when t changes from 60 to 20 A, respectively. All SLs show a thermal behavior of B γ ,2 affected by volume and interfacial contributions. The scandium thickness dependence of the volume contribution shows a surprisingly logarithmic behavior that indicates the existence of dislocations in the Dy blocks.

In situ layer-resolved magnetoelastic coupling and growth stress study of Co/Pd nanomultilayer films

Abstract We report on the layer-by-layer evolution of growth stress and magnetoelastic coupling (MEC) constant for the (6-A Co/20-A Pd)6 nanomultilayer film. Stress in Pd sublayer shows tensile stress up to the second Pd sublayer deposition, and it gradually changes to compressive after the deposition of the third Pd sublayer. We witness that MEC constant continuously increases on increasing the Pd layer thickness from 0 to 20 A. It is found that the evolution of the MEC constant is intimately related to the film strain rather than interface formation, and second-order strain correction is crucial to describe the dependence of the MEC constant on the Pd thickness.

Stress Concentration in a Soft Ferromagnetic with an Elliptic Inclusion in a Homogeneous Magnetic Field

The paper addresses a stress–strain problem for an infinite soft ferromagnetic body with an elliptic inclusion. The body is in a homogeneous magnetic field B01. The basic stress–strain characteristics and induced magnetic field in the body and inclusion are determined and their features in the neighborhood of the inclusion are studied. The magnetoelastic and Maxwell stresses are plotted against the ratio of ellipse axes and the latitude angle. Maximum stresses versus magnetic induction and mechanical and magnetic properties of the material are tabulated

Magnetoelastic stresses in a circular shell subject to a point magnetic source

The magnetoelastic problem of a circular shell subjected to the magnetic loadings is considered. In this paper the magnetic loadings include a point magnetic source in the domain outside or inside the circular shell or a uniform magnetic induction applied at infinity. Based upon the complex variable theory and the method of analytical continuation, the solutions of magnetic field quantities and the tangential magnetoelastic stresses in the shell and its outer and inner regions are obtained. The tangential magnetoelastic stresses for a thin shell in air under different magnetic loadings are also provided and compared with some special case of which the solution can be found in the literature, which reveals that the present solution is exact and general.

Observation of domain boundaries in a TbNi2B2C single crystal

The domain structure of TbNi2B2C was studied by the finest (⋍0 nm) magnetic-particle decoration below 13 K. The twin domain boundaries caused by magnetoelastic stresses were observed in the {110} planes.