Static Magnetostriction Research Articles

Magnetostrictive properties of the heavy-rare-earth-free Sm1-xNdxFe2 compounds

In this work, we report the magnetostrictive properties of Sm1-xNdxFe2 compounds, which are free of (expensive) heavy rare earths. Anomalies are observed in the temperature dependence of both the magnetization and the magnetostriction of these compounds, which are ascribed to spin-reorientation transitions. At low fields, the quasi-static magnetostriction and the piezomagnetic coefficient d33 of Sm0.88Nd0.12Fe2 are larger than those of SmFe2, which is due to the compensation of the anisotropy of the Sm3+ and Nd3+ ions. At a magnetic-field strength of 6 kOe, the static magnetostriction of Sm0.88Nd0.12Fe2 is −1244 ppm at 225 K and −1022 ppm at 290 K and, at a bias magnetic field of 700 Oe, the d33 equals 0.55 ppm/Oe (6.8 nm/A).

Magnetic properties of epoxy-bonded iron–gallium particulate composites

This paper presents the production process and the results of investigations into the microstructure and magnetic properties of epoxy-bonded iron–gallium (Galfenol) particulate composites. The manufactured composites consist of powdered Fe80Ga20 alloy particles of three different size distributions (ranging from 20 to 200 μm), bonded in an epoxy matrix with a filling factor of 0.80. The filling factor is defined as the ratio of the volume of Fe–Ga powder to the total volume of the composite’s constituents. The microstructure of the powdered alloy has been examined using x-ray diffractometry (XRD), and Mössbauer spectroscopy. Results for the measured magnetic hysteresis loop (B–H curve), static magnetostriction (λ) versus applied field and dynamic relative permeability (μr33) are presented for the alloy in the forms of bulk material, powders and composites subsequently manufactured. The highest value of magnetostriction (360 ppm) has been found in the composite with grain size in the range of 50–100 μm. On reversing the magnetic field direction, large magnetostrictive hysteresis for these samples has been observed. The value of μr33 at a given applied magnetic bias field has been found to decrease with decreasing particle size.

Influence of arrangement field on magnetostrictive and mechanical properties of magnetostrictive composites

Non-aligned and aligned polymer-bonded Tb 0.3Dy 0.7Fe 2 composites with 20% particle volume fraction were prepared under different arrangement fields (i.e. 0, 10 kA/m, 20 kA/m, 30 kA/m, 60 kA/m and 100 kA/m) during their gel process. Static magnetostriction, dynamic magnetostriction, elastic modulus and compressive strength of all specimens were tested and compared. Experimental results indicate that all the parameters are positively dependent on the arrangement field. The dependence is significant at low field levels, the critical value of which is 30 kA/m for the composites fabricated. No obvious improvement of the properties can be observed for a larger field. Such critical values are defined as the optimal arrangement field to manufacture magnetostrictive composites.

The effect of magnetic field heat treatment on magnetostriction of Terfenol-D 2-2 composites

Based on the analysis of the magnetostriction for Terfenol-D composites, Terfenol-D 2-2 magnetostrictive composites have been prepared with laminations perpendicular to [1 1 2] axes. Then one of the samples was annealed in the vacuum at 423 K for 15 min at the magnetic field of 240 kA/m, which is along the direction of laminations and vertical to the [1 1 2] axes of the specimen. The static magnetostriction λ and dynamic magnetostrictive coefficient d 33 of samples were measured under the compressive stress of 0, 2, 4, 6 and 8 MPa. Effects of the compressive stress and the magnetic field heat treatment on the magnetostriction λ have been investigated. It is found that the magnetostriction of 2-2 composites can be improved under the compressive stress when the magnetic field is larger than 20 kA/m. The magnetostriction of 2-2 composites with the magnetic field heat treatment increases under compressive stress, and it can reach 1390×10 −6 at the magnetic field of 200 kA/m and under the compressive stress of 4 MPa, much larger than the value of 860×10 −6 without the magnetic field heat treatment. The highest magnetostriction of the 2-2 composite with the magnetic field heat treatment can reach 1530×10 −6. The dynamic magnetostrictive coefficient d 33 of 2-2 composites with the magnetic field heat treatment have been improved, compared with that without magnetic field heat treatment. The maximum value of d 33 of the sample with magnetic field heat treatment is 71% larger than that without magnetic field heat treatment.

Magnetomechanical properties of single crystal Terfenol-D

Quasi-static and dynamic magnetomechanical measurements have been made on a twin-free oriented single crystal of Tb/sub 0.27/Dy/sub 0.73/Fe/sub 2/ (Terfenol-D). Unusually large values of dynamic strain coefficient, d/sub 33/, and magnetomechanical coupling coefficient, k/sub 33/, of 19.1 nm A/sup -1/ and 0.83 respectively were recorded with an oscillating field of amplitude 500 A m/sup -1/ rms at room temperature. The static magnetostriction saturated at 1688/spl times/10/sup -6/, however 90% of this strain was achieved with a field of 45 kA m/sup -1/. The strain versus magnetization curves exhibit unusually linear regions, allowing confirmation that 71/spl deg/ domain wall motion is primarily responsible for the high coupling coefficient of this material.

Comparison of the dynamic magnetomechanical properties of Tb0.27Dy0.73Fe2 and Tb0.30Dy0.70Fe2

Comparison is made between the magnetomechanical properties of Tb0.27Dy0.73Fe2 (27 Tb) and Tb0.30Dy0.70Fe2 (30 Tb), two commercially available compositions of the giant magnetostrictive alloy Terfenol-D. The quasi-static magnetostriction (as a function of bias field) and the dynamic strain coefficient (as a function of bias field and frequency) are shown for the two compositions at room temperature, using stress bias values of 0 and 9 MPa. The energy loss per cycle as a function of frequency is also given. The data for the static magnetostriction versus bias field shows 30 Tb to exhibit a significantly greater increase in initial slope and saturation strain when stress bias is applied compared to that seen for 27 Tb, which possesses superior magnetostriction at zero stress bias. A similar trend is observed in the data for the dynamic strain coefficient with 30 Tb again performing better under stress bias. The widening of the static strain hysteresis loop observed for stressed 30 Tb is seen to manifest itself in the low frequency energy loss per cycle; however 27 Tb is observed to possess the higher eddy current loss at 1 kHz. Data for the ratio d/χ, a quantity which is dependent only on magnetization processes and material constants, are shown which suggests that the application of a stress bias affects the magnetization processes, but differently for the two compositions.

Magnetic and magnetoelastic properties of TmPO4-type Jahn-Teller virtual elastics

The influence of the correlation of local Jahn-Teller deformations upon the magnetic and magnetoelastic properties of TmPO4-type virtual elastics is examined. This correlation leads to the appearance of contrary flexure points for the field dependence of the magnetic moment and changes the field and temperature behaviour of static magnetostriction. The results obtained are general for crystals, where operators of Zeeman interaction and Jahn-Teller molecular field commute.

Theory of negative magnetostriction in grain oriented 3% SiFe for various inductions and applied stresses

A theoretical model is presented to quantitatively account for the magnetostrictive behavior of grain oriented 3% SiFe laminations as a function of induction B and of applied tensile stress. Static magnetostriction measurements on high permeability longitudinal laminations show that the elongations Δ1/1 are negative for all B values, except close to saturation, reaching a deep minimum peak for <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B \cong 1.75</tex> T. The Δ1/1 and in particular the peak absolute values are found to strongly decrease upon application of longitudinal stresses (up to 12 kg/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ). In the model the behavior is considered of 90° spike domains, which characterize the surface of grains whose easy axis makes an angle ϑ with the lamination plane, to reduce the demagnetizing field energy. By minimizing the grain magnetic energies, the 90° domain volume is expressed as a function of the magnetization state. In particular it is found that spikes tend to disappear above a critical field which depends on the grain angle ϑ. The contributions to the magnetostrictive elongation deriving from these 90° domain volumes are then averaged over the actual distribution of grain orientations for the investigated g.o. material, and the theoretical curve is found to be in good agreement with the experimental one. The effect of stress is also considered, and it is shown that under tension the total 90° domain volume is strongly reduced, thus accounting, again in good agreement with the experiments, for the decrease of the negative magnetostriction peak amplitude.

The magnetostriction of grain-oriented 3 percent silicon-iron strips

In the course of the polarization process a magnetostriction of Goss and cube-textured strips of silicon-iron is caused by the appearance of transverse domains (closure structures, influence of imperfect grain orientation). The elongation of the strips is measured by an interference method. In the case of annealed Goss samples, the static magnetostriction λ( H) as a function of the external magnetic field H deviates by two additional extrema from the familiar “butterfly” curve. This anomaly disappears after a plastic deformation of 0.1%. Cube-textured strips yield a negative magnetostriction up to a field of 85 Oe. But, after a plastic deformation (0.1%), the magnetostrictive strain is positive and the curve λ( H) is identical with that of the deformed Goss samples. The influence of an elastic stress is also investigated, and the magnetostriction is discussed with respect to special domain structures.

Highly sensitive method of measuring magnetostriction

Above opticomechanical meter for measuring static magnetostriction of a different design to the existing ones has the following advantages: a constant magnification independent of the position of the light spot, greater sensitivity and the possibility of measuring both longitudinal and transverse magnetostriction.

Magnetic and Magnetostrictive Properties of Magnesium‐Nickel Ferrites

The purpose of this study was to determine whether or not the magnetic and magnetostrictive properties of mixed Ni‐Mg ferrites having various compositions were superior to those of a simple Ni ferrite. The preparation of the ferrites and the test methods are described briefly. The properties tested were Young's modulus, the remanence, the coercivity, the reversible permeability, the static magnetostriction, the electromechanical coupling coefficient, and the dynamic magnetostrictive constant. The results of the tests showed that the Ni ferrite was superior to the Ni‐Mg ferrites as far as magnetic and magnetostrictive properties were concerned.