J. P. Teter

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...

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.

Piezoelectric/magnetostrictive resonant inchworm motor

Magnetostrictive and piezoelectric materials were used to create a linear motor operating on the inchworm principle. This motor operates at an electrical resonance, switching power internally between inductive and capacitive components. Magnetic coils surrounding the two Terfenol-D rods which drive the inchworms center expanding element form the inductive component. Piezoelectric stacks that control the end clamping action are the capacitive components. The normal electrical phase relationship between these components provides natural drive timing for the inchworm. The motor direction can be easily reversed by changing the magnetic bias on the Terfenol. A prototype motor was built that achieved a stall load of 26 lb and no-load speed of 1 inch/sec vs the design of 30 lb and 1.3 inch/sec. A new type of power supply that switches power from a dc source was built for the motor. This power supply uses a small number of components to exactly supply the energy used in each inchworm cycle. It tracks the motor circuit resonance and is not affected by frequency shifts.

Magnetostrictive properties of Tb .3 Dy .7 (Fe 1-x Co x ) 1.9 and Tb .3 Dy .7 (Fe 1-x Ni x ) 1.9

Measurements of Curie temperature, magnetic moment and magnetostriction were made on Tb .3 Dy .7 (Fe 1-x T x ) 1.9 where T = Co and Ni ( 0 \leq x \leq 1 for Co and 0 \leq x \leq .08 for Ni). Alloys were prepared using a float zone technique, from which it was possible to grow oriented [112] crystallite samples for 0 \leq x \leq .21 (T = Co). The Curie temperature peaked near x = .25 (T = Co) and decreased with increasing x (T = Ni). For both alloy systems the room temperature magnetic moment decreased with increasing x. An increase in the rare earth contribution of the magnetostriction of 12% is predicted for the Co substituted alloys with values of x near .25. This increase was not confirmed by the magnetostriction measurements. A decrease in magnetostriction with increasing x was observed for all x. This may be due to a defected platelet structure in the oriented alloys ( x \neq 0 ), or a negative contribution to the magnetostriction from the Fe 1-x Co x sublattice.

Zero field damping capacity in (TbxDy1−x)Fey

Materials with a large capacity to dissipate mechanical energy are of interest for passive vibration damping. We have measured the zero‐field damping capacity of the giant magnetostrictive terbium–dysprosium–iron compounds by quasistatic stress–strain hysteresis loops. The magnetization and strain of the samples were measured for increasing and decreasing compressive stresses, up to 50 MPa. The zero‐field, room temperature damping capacity (ΔW/W) was calculated from the stress–strain loops and is plotted against maximum stress. The damping capacity maximum for the alloy with the nominal Terfenol‐D composition occurs at 4.1 MPa with the value 1.75 which corresponds to Q−1=0.28. The damping is almost independent of stress in a multi‐phase sample, (Tb0.6Dy0.4)Fe1.4, which contains both Laves phase and elemental rare earth.

Factors affecting performance of NiO biased giant magnetoresistance structures

We have made spin‐valve structures of Permalloy/Cu/Co by sputtering or electron‐beam deposition onto the antiferromagnetic oxide NiO. The oxides were made either by deposition of the metals and subsequent oxidation or by growing them in situ using reactive sputtering. The magnetic properties of the giant magnetoresistance structures were studied by magnetoresistance, vibrating sample magnetometry, and ferromagnetic resonance methods. The oxides were characterized by x‐ray diffraction and atomic force microscopy. We studied surface roughness and structure as functions of thickness and oxidation temperature and correlated the oxide properties with the magnetic performance. We found that the metal layer roughened during the postdeposition oxidation process and that the resulting oxide layers were very effective in pinning the direction of the magnetic moment of adjacent metal films. Coercive fields over 500 Oe were obtained for Co overlayers on NiO films but the exchange bias field was generally less than 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...

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

Optical observation of closure domains in Terfenol-D single crystals

Optical differential interference contrast microscopy is used to observe the topological features in surfaces of single crystal Terfenol-D (Tb/sub 0.3/Dy/sub 0.7/Fe/sub 1.95/) which arise from macroscopic lattice tilts due to the magnetostrictive strain between neighboring magnetic domains at the surface. The domain configurations observed can all be interpreted as being composed of low-energy 71 degrees and 109 degrees walls which have components of magnetization normal to the surface. Domain widths on the order of 2 mu m can readily be resolved. Observations from surfaces polished parallel to [110] and [112] are presented as a function of temperature, between 250 K and 350 K, and as a function of magnetic field applied parallel to the specimen surface. >