Magnetoelastic properties of Nd6Fe13Cu intermetallic compound

Magnetoelastic properties of Nd₆Fe₁₃Cu intermetallic compound are reported. To study the magnetoelastic behaviour of this compound, the thermal expansion as well as the longitudinal (λ_l) and transverse (λ_t) magnetostriction were measured by using the strain gauge method in the selected temperature range of 80-500 K under applied magnetic fields up to 1.5 T. An anomaly and invar-type effects are observed in the linear thermal expansion and α(T) curves at the Néel temperature. The linear spontaneous magnetostriction decreases sharply by approaching the Néel temperature and also shows the short-range magnetic ordering effects when antiferromagnetic-paramagnetic transition occurs. In the low field region, the absolute values of the anisotropic magnetostriction are small and then start to increase with applied magnetic field. Each isofield curve of the anisotropic magnetostriction passes through a minimum and then approaches to zero with increasing temperature. This magnetostriction compensation arises from the difference in the magnetoelastic coupling constants of the sublattices in this compound.     

Magnetoelastic fracture of soft ferromagnetic materials

Effects of magnetic field on fracture toughness of soft ferromagnetic materials were studied using experimental techniques and theoretical models. The manganese–zinc ferrite with a single-edge-notch-beam (SENB) were chosen to be the specimen and the Vickers’ indentation specimen subjected to a magnetic field were chosen to be the specimens. Results indicate that there is no significant variations of the measured fracture toughness of the manganese–zinc ferrite ceramic in the presence of the magnetic field. The theoretical model involves an anti-plane shear crack with finite length in an infinite magnetostrictive body where an in-plane magnetic field prevails at infinity. Magnetoelasticity is used. The crack-tip elastic field is different from that of the classical mode III fracture problem. Furthermore, the magnetoelastic fracture of the soft ferromagnetic material was studied by solving the stress field for a soft ferromagnetic plane with a center-through elliptical crack. The stress field at the tip of a slender elliptical crack is obtained for which only external magnetic field normal to the major axis of the ellipse is applied at infinity. The results indicate that the near field stresses are governed by the magnetostriction and permeability of the soft ferromagnetic material. The induction magnetostrictive modulus is a key parameter for finding whether magnetostriction or magnetic-force-induced deformation is dominant near the front an elliptically-shaped crack. The influence of the magnetic field on the apparent toughness of a soft ferromagnetic material with a crack-like flaw can be regarded approximately in two ways: one possesses a large induction magnetostrictive modulus and the other has a small modulus. Finally, a small-scale magnetic-yielding model was developed on the basis of linear magnetization to interpret the experimental results related to the fracture of the manganese–zinc ferrite ceramics under magnetic field. Studied also is the fracture test of the soft ferromagnetic steel with compact tension specimens published in the existing literature.     

On an initial boundary value problem in nonlinear 3D-magnetoelasticity

We prove existence and uniqueness of a weak solution to an initial boundary value problem, related to the Maxwell and Lamé systems nonlinearly coupled through the so-called magnetoelastic effect. Uniqueness is proved under additional assumptions on the smoothness of the solution.     

Stress and magnetic field-dependent Young's modulus in single crystal iron-gallium alloys

The variability in Young's modulus of single crystal iron-gallium (Galfenol) alloys having 16, 17.5, 19, 24.7 and 29 at% gallium is investigated using experiments and simulations. Some of these alloys showed more than 60% change in Young's modulus along the 〈1 0 0〉 directions on varying their magnetization and stress states compared to their modulus at magnetic saturation. A function, ΔE(σ,H), is defined such that the variability of modulus is bound between 0% and 100%. The observations are related to the inherent magnetomechanical coupling in the material. An energy-based non-linear constitutive model is used to predict the variable modulus in Galfenol as a continuous function of stress and magnetic field. Model predictions showed good correlation with experimental results.     

The temperature dependence of the magnetoelastic characteristics of cores for force sensors utilizing Fe<Subscript>70</Subscript>Ni<Subscript>8</Subscript>Si<Subscript>10</Subscript>B<Subscript>12</Subscript> amorphous alloy

This paper presents the results of investigation on the influence of temperature on magnetoelastic characteristics of the two ring-shaped cores, made of Fe₇₀Ni₈Si₁₀B₁₂ amorphous alloy. The cores were annealed for 1 h at 350 and 400°C, respectively. The compressive force F was applied perpendicular to the direction of the magnetizing field H in the sample. Special cylindrical backing enables application of the uniform compressive stress σ to the wound ring sample. A resistive furnace heated the experimental set-up. Results presented in the paper indicate a significant influence of the temperature on the magnetoelastic characteristics of Fe₇₀Ni₈Si₁₀B₁₂ amorphous alloy. Information about the magnetoelastic characteristics of this material may be useful in the magnetoelastic sensor development. Also this will create new possibilities in the development of physical model of magnetoelastic effect.      

On a hyperbolic-parabolic system arising in magnetoelasticity

The evolution of a magnetoelastic material is described by a nonlinear hyperbolic-parabolic system. We introduce a simplified but nontrivial model and prove the existence of a unique solution to the corresponding initial boundary value problem.     

A comparative study of the magnetoelastic properties of the YFe10V2 and NdFe10V2 compounds

The magnetoelastic properties of iron-rich REFe₁₀V₂ (RE=Nd, Y) compounds were studied via magnetostriction and thermal expansion measurements in the 5–300 K range of temperature in up to 6 T external fields. Results of thermal expansion analysis show that the spontaneous magnetostriction of the compounds mostly originates from itinerant magnetization. Besides, the small volume striction appearing in the thermal expansion of the Nd compound close to 50 K suggests the existence of a basal to conical spin re-orientation transition. The volume magnetostriction isotherms of both compounds take minimum values for external field corresponding to the anisotropy field. In addition, the anisotropic and the volume magnetostriction traces of the NdFe₁₀V₂ take marked maxima under low field, with a relatively large initial magnetostrictivity, again more pronounced at the conical–axial spin re-orientation transition (T_SR=130 K). Analysis of the anisotropic magnetostriction of the Nd compound leads to the conclusion that the contribution of Nd–Fe interactions is negligible. The temperature dependence of volume magnetostriction is in good agreement with prediction of a phenomenological model based upon a fluctuating local band theory. This analysis shows that the difference between the forced volume strictions of Y and Nd compounds below and above T_SR originates from the Nd sublattice magnetization.     

Exactly soluble magnetoelastic lattice with a magnetic phase transition

We examine the soluble magnetoelastic Ising model developed by Baker and Essam and give a detailed discussion of its thermodynamic properties. Particular attention is devoted to the properties of the magnetic phase transition at zero field, which is found to be either first order or second order, depending on whether the experiment is performed at negative or positive pressure.Part of this work was done while L. G. was visiting Tel Aviv University. Research supported by National Science Foundation Grant No. GP. 16025 to L. G.     

Buckling of a beam subjected to electromagnetic force and its stabilization by controlling the perturbation of the bifurcation

For a beam subjected to electromagnetic force, magnetoelastic buckling due to the increase of such force is theoretically investigated by taking account of the nonlinearity of the electromagnetic force and the elastic force of the beam. Using Liapunov-Schmidt method and center manifold theory, the equilibrium space, the bifurcation set and the bifurcation diagram are theoretically derived. Also, the effect of the higher modes other than the buckling mode on the mode shape of the postbuckling state is discussed. Furthermore, a control method to stabilize the magnetoelastic buckling is proposed, and the unstable equilibrium state of the beam in the postbuckling state, i.e., the straight position of the beam, is stabilized by controlling the perturbation of the bifurcation.