J.F. Lindberg

MAGNETIZATION AND MAGNETOSTRICTION OF DENDRITIC 112 TBXDYYHOZFE1.95 (X+Y+Z=1) RODS UNDER COMPRESSIVE STRESS

The field dependencies of the magnetization and magnetostriction of the Laves phase pseudobinary TbxDyyHozFe1.95 (x+y+z=1) compounds were measured as a function of compressive stress T (10 MPa<|T|<70 MPa) and applied magnetic field H (0<H<135 kA/m). Values of x, y, and z were chosen to obtain minimum magnetic anisotropy and easy magnetization axis rotation near room temperature. At a compressive stress of 34 MPa, the addition of Ho to the binary Tb1−xDyxFe1.95 compound reduced the width of the strain versus magnetic field hysteresis curves in Tb0.28Dy0.57Ho0.15Fe1.95 and Tb0.26Dy0.54Ho0.2Fe1.95 by 23% and 54%, respectively, compared to the original alloy, while the strains were reduced by only 7% and 10%.

Magnetomechanical coupling in Bridgman‐grown Tb0.3Dy0.7Fe1.9 at high drive levels

It is now possible to achieve substantial magnetomechanical transduction in modified Bridgman‐grown samples of Tb0.3Dy0.7Fe1.9 (Terfenol‐D) which are grain‐oriented to achieve nearly complete [112] alignment. Large magnetic‐field excursions can be converted into large fractional dimension changes (ΔL/L>10−3). In this paper measurements are reported of the average magnetomechanical coupling factor determined by (i) large field drives (>1000 Oe) and (ii) large pressure changes (> 20 MPa). By extending the small‐signal magnetomechanical expressions to difference relationships Δe=sH Δσ+d ΔH and ΔB=d*Δσ+μσ ΔH, it is possible to determine large‐signal coupling factors by k2=1−μe/μσ, and (2) k2=1−sB/sH. Here μe and μσ are the average magnetic permeabilities (ΔB/ΔH) at constant strain e, and at constant stress σ, and sB and sH are the large signal elastic compliances (Δe/Δσ) at constant induction B, and constant field H. The square of the coupling factor is defined by k2=1−dd*/sHμσ. Using an apparatus which was d...

Magnetoelastic coupling and ΔE effect in TbxDy1−x single crystals

The elastic moduli of the highly magnetostrictive TbxDy1−x alloys (x=0.5, 0.6, and 0.67) were measured at 77 K under conditions of constant magnetic field and constant magnetic induction. From these values the magnetic contribution to the moduli (intrinsic ΔE effect) and magnetoelastic coupling factor k were calculated. For Young’s moduli measured under constant flux density (magnetically blocked conditions), it was found that EB∼20 to 50 GPa. For measurements made while maintaining a constant magnetic field (magnetically free conditions), it was found that Young’s moduli EH minima range from ∼3 to 5 GPa. Such large differences between EB and EH yield magnetoelastic coupling factors in excess of 0.9. Theoretical expressions of the magnetic contribution to the elastic compliance, (1/EH−1/EB), were derived using the single vector magnetization rotation model.

Development of Terfenol-D transducer material

Terfenol-D, Tb1−xDyxFe2 (x≅0.7), is successfully used as a magnetostrictive transducer material for low-frequency applications. To extend the frequency range of magnetostrictive transducers into the high kHz and MHz range, new materials processing techniques must be developed to minimize eddy current losses. The method that has demonstrated the greatest potential to date is based on rapid solidification by melt spinning to obtain thin strips of material. The objective of this program includes refining the casting procedure to yield ribbons with the [111] direction oriented along the length of the ribbon, with the (110) plane in the plane of the ribbon. The crystallographic orientation of the Terfenol-D ribbons have been controlled by varying the cooling rate of the melt-spinning process. The cooling rates were controlled by a number of parameters in the melt-spinning process and ribbons have been obtained with an enhancement of the (110) plane parallel to the surface of the ribbon. Magnetostrictive measur...

Piezomagnetic properties and ΔE effect in TbZn at 77 K

Abstract Youngs modulus, magnetization and magnetostriction measurements were made as a function of applied magnetic field (0 H σ d -constants greater than 300 nm/A and changes in Youngs modulus greater than 40 GPa were found. Magnetomechanical coupling factors reached 0.94.

Magnetostriction and magnetomechanical coupling of grain oriented Tb/sub 0.6/Dy/sub 0.4/ sheet

The magnetostriction, magnetization, and Youngs moduli were measured on laminated rods on thin hot rolled sheets of Tb/sub 0.6/Dy/sub 0.4/ at 77 K. The results were compared to those obtained on single crystals. Approximately 65% of the single crystal saturation magnetostriction was achieved in the rolled samples. While the hot rolling produces the desired planar texture the magnetostriction and magnetomechanical coupling strongly depend upon the final heat treatment. >

Magnetic properties of RZn with R=Tb/sub 1-x/Dy/sub x/ (0/spl les/x/spl les/0.6) and R=Tb/sub 1-y/Gd/sub y/ (0/spl les/y/spl les/0.4)

Magnetization, Youngs moduli, and magnetostriction were measured on polycrystalline samples of Tb/sub 1-x/Dy/sub x/Zn and Tb/sub 1-y/Gd/sub y/Zn. The easy axis phase boundary was determined for 0/spl les/x/spl les/0.6 and 0/spl les/y/spl les/0.4. To derive temperature dependencies of Youngs moduli, small transducer rings were excited into resonance at frequencies /spl sim/100 kHz. Estimated magnetomechanical coupling factors of polycrystalline Tb/sub 0.8/Gd/sub 0.2/Zn in the region of easy axis reorientation are /spl sim/0.6. Magnetostrictions of polycrystalline TbZn at 77 K saturated at /spl sim/0.2% with relatively low fields (/spl sim/1000 Oe), even for compressive stresses >40 MPa.

Application of high-temperature superconducting wires to magnetostrictive transducers for underwater sonar

Recently discovered cryogenic magnetostrictive materials show maximum strains greater than any room temperature materials. These cryogenic magnetostrictors can be combined with high-temperature superconducting (HTS) coils to create a sonar transducer with high efficiency and high acoustic-power density. A prototype low-frequency ( >