D. G. Lord

Application of the Villari effect to electric power harvesting

Transducers utilizing the Villari effect (inverse-magnetostrictive effect) consist of a coil wound on a core of magnetostrictive material. In this paper, a linear magnetomechanical coupling model is developed to analytically calculate the potential electrical power such transducers can generate when subjected to applied harmonic mechanical vibration. Two vibration modes, force driven and displacement driven, are distinguished. The eddy current effect in the magnetostrictive core material and the leakage inductance of the coil are taken into account. Comparisons of output electrical power are presented for Terfenol-D and Galfenol magnetostrictive cores.

Magnetostriction in TbDyFe thin films

Magnetization and magnetostriction in amorphous binary TbFe and DyFe and amorphous and polycrystalline, ternary (TbxDy1−x)yFe100−y thin films have been investigated. The measurements reflect the compositional dependence of the easy direction of magnetization in the films. In plane magnetostrictions of over 300×10−6 were measured for some of the amorphous TbFe and TbDyFe films and values greater than 750×10−6 were obtained in polycrystalline TbDyFe films near to the Terfenol composition.

Giant magnetoresistance in sputter deposited Co/Cu multilayer systems

This paper presents some results of magnetoresistance measurements on sputter deposited Co/Cu thin film multilayers. We find that large values of magnetoresistance approaching 40% can be obtained and that these values oscillate in magnitude with the thickness of the non-magnetic spacing layer with a period of about 1.1 nm. It appears that the multilayer must be grown on a particular form of underlayer to realize these large values of magnetoresistance ratio.

Magnetic domains and microstructural defects in Terfenol‐D

The ternary alloy Tb0.3Dy0.7Fe2 (Terfenol‐D) is of significant technological interest as it possesses the largest known magnetostriction to anisotropy ratio near room temperature. Results of microstructural and magnetic domain observations by Lorentz microscopy and reflection x‐ray topography are presented from both stoichiometric twinned single crystals prepared by a free‐standing zoning technique, and pseudo single crystals prepared by the Czochralski method. Direct evidence of wall interactions with dislocations, twin boundaries and precipitates are presented which demonstrate the complex interaction between the magnetic and strain energies within this material.

Magnetic properties and microstructure of giant magnetostrictive TbFe/FeCo multilayers

Magnetostrictive multilayer films which combine exchange coupled giant magnetostrictive materials (amorphous Tb0.4Fe0.6) and soft magnetic materials with large polarizations and considerable magnetostriction (crystalline Fe0.5Co0.5) were prepared by magnetron sputtering. The microstructure and the magnetic properties of these multilayers were investigated as a function of the annealing temperatures and the corresponding film stresses. Giant magnetoelastic coupling coefficients (or magnetostrictions) are achieved at low fields, due to the magnetic polarization enhancement in such multilayers, the optimized stress state, and a suitable microstructure. For these optimized Tb0.4Fe0.6(7 nm)/Fe0.5Co0.5(9 nm) multilayers a saturation magnetoelastic coupling coefficient of 27.5 MPa at 20 mT and a coercive field of 2 mT has been achieved.

MAGNETOSTRICTION IN POLYCRYSTALLINE SPUTTER-DEPOSITED TBDYFE FILMS

Magnetic and microstructural investigations of some polycrystalline rare‐earth—transition‐metal (RE‐TM) alloy thin films are reported. Emphasis was placed on pseudobinary alloys in the (TbxDy1−x)Fe2 and (TbxDy1−x)3Fe4 systems. The films were prepared by sputter deposition onto both room‐temperature and high‐temperature substrates. Films prepared on room‐temperature substrates were amorphous and were crystallized by postdeposition annealing. Transmission electron microscopy and x‐ray diffraction showed and indicated a complex microstructure consisting of small grains of free iron, REFe compounds, and some RE oxide phases. Magnetization, coercivity, and magnetostriction measurements showed the films to be essentially magnetized in plane with a trend across the composition range which reflected the different influences of Tb and Dy and also the compensation condition. Magnetostriction values greater than 0.75×10−3 were found near the Terfenol composition Tb0.27Dy0.73Fe2 and for x≳0.3.

Study of the magnetorestrictive distortion in single crystal terfenol-D by x-ray diffraction

X-ray diffraction has been used to study the magnetostrictive distortion in single-crystal Terfenol-D. The magnetostriction coefficient and the linear thermal-expansion coefficient have been determined over the temperature range of +or-100 degrees C from observing the change in shape, diffraction angle, and intensity of the

Microstructure and magnetic properties of Tb-Dy-Fe/sub 1.9/

Materials of the composition Tb/sub x/Dy/sub 1-x/Fe/sub 1.9/ (x=0.27, 0.3, and 0.5), have been prepared by a contained float-zone growth technique. These materials have been found to exhibit magnetostrictive strains greater than 1000 microstrain with magnetomechanical coupling coefficients on the order of 0.6. Microstructural investigations have highlighted the complex relationship between the magnetic domain structure and the inherent defect structure of the materials. All alloys were prepared using sublimed-quality rare earth metals and spec-pure iron. Microstructure observations were carried out using both optical and electron microscopes. The strain measurements were made using conventional techniques. The measurement of the magnetomechanical coupling coefficient (k/sub 33/) was carried out using a resonance method. >

Surface deformations and domains in Terfenol-D by scanning probe microscopy

This paper reports the first direct measurements of the deformations in the surface of a ferromagnet caused by magnetostrictive lattice strains in neighboring magnetic domains. Observations of the {011} and {112} surfaces of twinned Terfenol‐D (Tb0.3Dy0.7Fe2) crystals by atomic force microscopy reveal the deformation domains previously imaged by optical microscopy and predicted by recent theory. The surface topography has been imaged in the remanent and ac demagnetized states and measurements of the deformation gradients have enabled the magnetostriction constant in the 〈111〉 direction to be estimated as 1.63×10−3 to within 8%. All theoretically predicted deformation domains have been observed and, in particular, the exact compatibility of such deformations across the growth twin boundaries is clearly revealed. The magnetic domains associated with the observed deformations are inferred from magnetic force microscopy observations which yield complex contrast patterns.

Transmission electron microscopy of Terfenol‐D crystals

Magnetic domain and microstructure observations are presented from samples of pseudo‐single‐crystal Terfenol‐D examined by transmission electron microscopy (TEM). This ternary alloy is of significant technological interest since it exhibits the highest known magnetostriction to anisotropy ratio near room temperature. Specimens for TEM studies in (110), (111), and (112) orientations have also shown regions of unusual diffraction contrast in bright field which appears to be very sensitive to specimen tilt. Lorentz mode TEM has subsequently shown such regions to correspond exactly with magnetic domains. This contrast is attributed to the high magnetostrictive strain causing a local distortion of the lattice and thus a local deviation from the Bragg condition. This conclusion has been investigated and supported by TEM observations with the samples cooled below the spin reorientation temperature. When this transition is reached the diffraction contrast in bright field is considerably decreased and cannot be ma...