J.R. Cullen

Magnetostriction of Terfenol-D heat treated under compressive stress

Heat treatment at temperatures >835/spl deg/C and compressive stresses >80 MPa substantially increased the magnetostrictive performance of Terfenol-D (Tb/sub 0.3/Dy/sub 0.7/Fe/sub 1.92/) under the condition of zero loading. This heat treatment created a built-in prestress which significantly increased the low stress magnetostriction and substantially altered the magnetization curve by reducing its initial susceptibility. For measurements at compressive stresses >15 MPa the effect of the built-in stress was minimal and the magnetostrictive performance was not appreciably altered.

Effect of applied stress on the magnetization of amorphous magnetoelastic wires

The magnetization of transversely annealed metallic glass wires (Fe/sub 77.5/B/sub 15/Si/sub 7.5/) was examined as a function of longitudinal stress and torsional strain. The effect of annealing parameters on magnetoelastic coupling of the wires was measured. The wires differ from ribbons of similar composition in several important respects. The domain configuration appears to consist of a longitudinally oriented core region surrounded by a sheath consisting of transverse domains. The surface transverse domains were directly observed by an optical imaging technique. Magnetization of unstressed wires proceeds by a two-step process. Application of 3 MPa stress alters the domain configuration, leading to longitudinal 180 degrees domain walls throughout the wire. The additional imposition of torsional strain leads to a subcritical bifurcation. It was found that, unlike ribbons, wires annealed with the magnetic field off during the heating portion of the annealing cycle have different magnetoelastic properties from samples annealed with the field on throughout the annealing process. >

Critical behavior of cubic magnetostrictive materials under stress

Critical points and lines in magnetic field space define the boundaries of different magnetization states between which the magnetization may “jump,” leading to hysteresis. We calculate the changes in these boundaries due to magnetoelastic coupling to applied stresses, and obtain the critical stresses required to eliminate jumping in specific cases. These results may provide a way of reducing or eliminating hysteresis in large magnetostriction materials.

Magnetic and magnetoelastic properties of single crystal Tb/sub 0.5/Dy/sub 0.5/Zn

Magnetization, magnetostriction, and modulus measurements have been performed on single crystal specimens of the pseudobinary Tb/sub 0.5/Dy/sub 0.5/Zn. Non-principal axis easy magnetization directions were observed in the (001) plane at temperatures below 20 K. At all temperatures, [110] is the hard axis. At 2.2/spl deg/K the anisotropy field is estimated to be 5.6 MA/m (70 kOe). Magnetostriction and modulus measurements at 77 K showed a saturation magnetostriction of /spl sim/5/spl times/10/sup -3/ and a modulus that varied from 10-60 MPa depending on field.

Magnetization and magnetostriction of Tb1−xDyxZn single crystals

Magnetization, magnetostriction, and elastic modulus measurements were made on single crystal specimens of Tb1−xDyxZn. Easy axis magnetization rotation as much as 26° were observed in the (001) plane of Tb0.75Dy0.25Zn below 33 K. From these measurements, values of the K4/K8 anisotropy ratios were calculated. No easy axis magnetization rotation was observed in the x=0.6 and x=0.8 single crystals. Magnetostriction and modulus measurements at 77 K in Tb0.4Dy0.6Zn showed a saturation magnetostriction of ∼5×10−3 and a maximum magnetomechanical coupling factor of 0.96.

Anomolous ΔE effects in TbDyZn alloys

The temperature dependence of Young’s modulus has been measured for a series of Tb1−x Dy x Zn pseudobinary compounds with x ranging from 0 to 1. From the sharp dips in the modulus vs temperature data, the reorientation transition temperatures have been determined, and the magnetic phase diagram deduced. Magnetization measurements taken on the same samples show less pronounced features at the corresponding temperatures.

Multiple easy-axis changes in magnetostrictive Tb/sub 0.88/Dy/sub 0.12/Zn

Magnetization measurements were made on a single crystal sample of Tb/sub 0.88/Dy/sub 0.12/Zn from 4 K to room temperature. Easy-axis reorientations were found at about 46 K, 42.5 K, and 10 K. The presences of [100] easy, [uv0] easy and [110] easy and a return to a second [uv0] easy phase were deduced from these data. A discontinuous change in easy direction at 63 K was found for a TbZn single crystal. Magnetostriction measurements were made under compression at 77 K on a single crystal rod of Tb/sub 0.88/Dy/sub 0.12/Zn. /spl lambda//sub 100/ was determined to be 0.53%. An interpretation of the magnetization vs. magnetic field orientation data is given based on a phenomenological model. In particular, it is noted that two maxima in the magnetization vs. orientation curves are consequences of low magnetic anisotropy; they do not imply the coexistence of two free energy minima.

Magnetic and Magnetoelastic Studies of Single Crystal Tb/sub 0.6/Dy/sub 0.4/Zn At Low Temperatures

The alloy series Tb/sub 1-x/Dy/sub x/Zn, x/spl les/0.6, has been shown to undergo easy-axis reorientations at low temperatures. In this paper results of magnetization on single crystal disks of Tb/sub 0.6/Dy/sub 0.4/Zn are reported, Maxima in the magnetization as much as 15/spl deg/ from the axes were found below T/sub R//spl cong/20 K. Magnetostrictions of 5/spl times/10/sup -3/ were measured at 77 K on single crystal rods. Magnetization versus field curves under a series of compressive stresses have verified the highly magnetoelastic nature of this alloy. The non-principal magnetization orientations are discussed on a phenomenological model which includes an eighth-order anisotropy term.

Magnetic properties of Tb/sub 1-x/Nd/sub x/Cd

Magnetic moment measurements on a series of Tb/sub 1-x/Nd/sub x/Cd pseudobinary alloys have been carried out from helium temperatures to room temperatures and in magnetic fields up to 1.4 MA/m. The Curie temperatures are observed to initially increase as Nd is substituted for Tb, with a maximum at x/spl cong/0.25. Ferromagnetic coupling of the Tb-Nd spins results in antiparallel Tb (heavy rare earth) and Nd (light rare earth) magnetic moments throughout the series, with magnetization cancellation at x/spl cong/0.75. Sharp maxima in the magnetizations at temperatures below their respective Curie points are interpreted as marking magnetization reorientation temperatures.

Magnetic anisotropy in Terfenol-D thin films (abstract)

Thin-film Terfenol-D has attracted considerable attention for applications as microactuators and sensors. Depending on applications, the magnetic anisotropy plays a key role in physical property control. In this paper, the magnetic anisotropy of sputter-deposited Terfenol-D thin films on single-crystal Si substrates was studied by both dynamic torque and magnetization measurements. The evolution of magnetic anisotropy in the course of annealing treatment was followed by both types of experiments. It was found that there is a strong growth-induced anisotropy in the as-grown amorphous films, which is attributed to Fe–rare-earth bond orientation anisotropy. In samples treated at high temperatures, this growth-induced anistropy is overshadowed by the elastic anisotropy resulting from the substantial stresses in the films of giant magnetostrictive material. Domain patterns of different kinds of anisotropy were also monitored using a magnetic force microscope. The consequences of the growth-induced and elastoma...