A. E. Clark

Anisotropy compensation and magnetostriction in TbxDy1−x(Fe1−yTy)1.9 (T=Co,Mn)

From magnetization (M) and magnetostriction (λ) measurements as a function of magnetic field and stress, the temperatures of anisotropy compensation, Tm, for technologically important TbxDy1−x(Fe1−yTy)1.9 [T=Co,Mn (0.3≤x≤0.5) (0≤y≤0.3)] were determined. Measurements of M and λ encompassing Tm were made under compressive stresses from 8.8 to 36 MPa and for temperatures from −196 to +130 °C. In agreement with earlier measurements, Tm decreases with increasing Tb. Substitution of Mn for Fe for fixed x also decreases Tm. In contrast with these observations is the increase of the anisotropy compensation temperature with the replacement of Fe by small amounts of Co. In the cases of both (1) increasing Tb content and (2) increasing Co content, the Curie temperature TC increases, yielding, in general, a higher magnetic moment and saturation magnetostriction of these alloys. Thus, compensation at a given temperature may be obtained in an improved class of Laves phase compounds, R(1)xR(2)1−x(Fe1−yCoy)2, where rare ...

Anisotropic perpendicular axis magnetostriction in twinned TbxDy1-xFe1.95

The longitudinal magnetostriction (Δl/l) for twinned TbxDy1−xFe1.95 material, prepared by the free‐standing float‐zone method, has been previously measured and found to be very large (2000×10−6) at room temperature. The magnetostrictions for the [111] and [110] crystallographic axes perpendicular to the applied stress and magnetic‐field [112] direction are presented as functions of temperature, applied stress, and applied magnetic field. The temperature range is ±60 °C centered about the anisotropy compensation temperature of Terfenol‐D (+10 °C). The stress ranges from 2 to 32 MPa and the magnetic field to ±2000 Oe. The temperature dependence of the perpendicular axes magnetostriction is similar to that of the conventional magnetostriction measured parallel to the [112] growth axis. Relative values for the saturation magnetostriction exhibit a large anisotropy in the perpendicular direction, ranging from −117% for the [111] to +19% for the [110] direction. This ratio stays constant as a function of te...

A new method of magnetostrictivity and magnetostriction measurement

The magnetostrictivity (d) and magnetostriction ( lambda ) of high coupling magnetomechanical amorphous ribbons and wires are determined without the use of a direct magnetomechanical measurement. The method relies on an easily measured magnetic property (permeability) of the magnetostrictive material obtained under the conditions of constant stress and constant strain ( mu /sup c/). The magnetomechanical nature of the measurement enters through mu /sup c/. Experimental results are compared to predictions made on the basis of the single-vector magnetization rotation model. The effect of demagnetization on the magnetostrictivity and coupling factor is also calculated for long thin ribbons and wires. >

Preisach modeling of hysteresis in Terfenol

Terfenol (Tb0.3Dy0.7Fe1.9) and related materials have proven useful as electromechanical transducers. As with other transducers, these materials exhibit hysteresis, which must be included in any model of the transducer. Preisach theory is one of the available models that includes the effects of hysteresis. The theory is able to include the hysteresis by maintaining a history of the field reversals in the material. Both the strain and magnetization hysteresis loops in a 3.8‐cm‐diam Terfenol rod have been measured under 20.7‐MPa longitudinal stress. The data has been used to derive a Preisach model of the rod, including hysteresis effects. It is possible to predict the strain and magnetization of the rod, including minor loops, with about 10%–15% accuracy.

Structure of melt-spun Fe-Ga based magnetostrictive alloys

Fe/sub 1-x/Ga/sub x/ (x=0.17, 0.21, 0.25 and 0.3) alloys were rapidly quenched by the melt-spinning technique to determine the maximum Ga concentration that retains the disordered bcc (/spl alpha/-Fe) phase at room temperature. The texture of the ribbons as a function of melt-spinning parameters and annealing was also extensively studied. All of the as-spun samples were found to be crystalline. For x=0.17, only the disordered bcc phase was found and for x=0.25 and 0.3, primarily DO/sub 3/ phase was found, while for x=0.21, the phase is bcc at high wheel speed and DO/sub 3/ at low speed. For the free side of the as-spun ribbons, the easy growth axis of /spl alpha/-Fe or of DO/sub 3/ tilts about 10/spl deg/ to 20/spl deg/ from the ribbon normal and is along the ribbon length. This texture does not change significantly with wheel speed. The texture on the wheel side of the ribbon is close to random at high speed but increases with slower speed. For Fe/sub 83/Ga/sub 17/, 900/spl deg/C annealing reduces the tilt angle while 1100/spl deg/C annealing recrystallizes the grains and produces strong out of plane texture but randomizes the directionality in the plane. Annealing with sulfur addition was found to enhance the {100} texture but did not produce the desired along the longitudinal direction of the ribbon. The saturation magnetostriction, /spl lambda//sub s/, of as-spun Fe/sub 79/Ga/sub 21/ and Fe/sub 83/Ga/sub 17/ both having a disordered bcc structure and strong {100} texture was measured as 98 and 130 ppm, respectively, along the ribbon length.

Magnetomechanical damping in giant magnetostriction alloys

Magnetomechanical damping in the giant magnetostriction material Terfenol-D has been investigated by quasi-static stress-strain measurements and modeled theoretically. The damping capacity is a strong function of applied stress amplitude, increasing to a maximum at some finite stress and then decreasing slowly at still larger applied stresses. Maximum damping capacities greater than 1.0 were observed for the lowest magnetic bias fields and prestresses at applied stress amplitudes of 4 MPa. Both the qualitative behavior of the damping and its magnitude are successfully described by a model of abrupt magnetization jumps within individual domains driven by the applied stress.

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...

Magnetostriction and hysteresis for Mn substitutions in (Tb/sub x/Dy/sub 1-x/)(Mn/sub 1/Fe/sub 1-y/)/sub 1.95/

A study of the effects of substituting small amounts of manganese for iron in the terbium-dysprosium iron/sub 2/ Laves-phase intermetallic system is presented. Pseudocrystalline (twinned single-crystal) rods of Mn-substituted Terfenol-D (Tb/sub x/Dy/sub 1-x/Fe/sub 2/; x=0.3, 0.4, 0.5, 0.6) were prepared by free-standing-zone methods such that the

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.

Magnetostriction of Dy-rich Tb/sub x/Dy/sub 1-x/ single crystals

Magnetostriction and differential scanning calorimetry measurements were conducted on the Tb/sub x/Dy/sub 1-x/ alloy system for 0.33>or=x>or=0. The magnetostriction measurements extend from 80 K to 300 K and cover the ferromagnetic, antiferromagnetic spiral, and paramagnetic temperature regions with fields of 6-20 kOe. From the data the authors derive the two lowest order magnetostriction constants, lambda /sup gamma .2/ and lambda /sup gamma .4/, as well as the basal plane anisotropy, K/sub 6//sup 6/. At 80 K, lambda /sup gamma .2/>7*10/sup -3/ for all alloys. While lambda /sup gamma .2/ is almost independent of alloy concentration (except at high temperatures), lambda /sup gamma .4/ decreases substantially with increasing Dy concentration, approaching zero for 0.17>x>0. As reported previously, the basal plane anisotropy was found to compensate at temperatures below 100 K in the x=0.67 and 0.50 alloys. This compensation is found to occur at higher temperatures in the x=0.33 and 0.17 alloys. The temperatures at which this occurs are presented in a magnetic phase diagram along with the calorimetrically determined Curie and Neel temperatures. >