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The stress-strain hysteresis losses of [Tb.sub.x] [Dy.sub.1-x] [Fe.sub.1.92] (x = 0.30, 0.33, 0.40, 0.45, and 0.50) were measured at a variety of magnetic fields between 0 and 1600 Oe. Stress ranges from ~0 to -10, -20, -40, and -60 MPa (the minus sign indicates compressive stresses) were used. The hysteresis loop area increased from 5.7 kJ/[m.sup.3] at x = 0.30 to 10 kJ/[m.sup.3] at x = 0.50 as the Tb concentration and the magnetic anisotropy increased. The position of the hysteresis loop shifted to larger compressive stresses as the magnetic field was increased allowing the strength of the damping to be controlled by the magnetic field. Index Terms--Hysteresis, magnetomechanical damping, Terfenol.

The magnetostriction ([[Lambda].sub.100]) of b.c.c. Fe is increased over 10-fold at room temperature by the substitution of ~20% gallium for Fe. [Fe.sub.1-x][Ga.sub.x] alloys with x between 0.19 and 0.214 that are quenched from 800 [degrees] C exhibit magnetostrictions ~25% higher than those furnace-cooled at 10 [degrees]/min. We propose that this great increase of magnetostriction above that of Fe in Fe-Ga alloys is not due to conventional magnetoelastic effects but due to the substitutive presence of asymmetrically shaped clusters of the Ga atoms. As the concentration of solute atoms approaches 25%, the lattice becomes relaxed with formation of a more ordered structure and the magnetostriction decreases in value. Index Terms--Actuator, iron-gallium alloys, magnetostriction, structural materials, transduction.

The magnetic and magnetostrictive properties of [Fe.sub.1-x][Ga.sub.x] and [Fe.sub.1-x-y][Ga.sub.x][Al.sub.y] (x + y [is less than] 0.3) single crystals were measured under compressive stresses up to 120 MPa and in magnetic fields up to 1 kOe. Values of [[Lambda].sub.100] exceeding 200 ppm were observed in samples of [Fe.sub.83][Ga.sub.17] from 180 K to room temperature. Only a small monotonic decrease in magnetostriction with temperature was found. On the other hand, [[Lambda].sub.111] maintained small negative values close to those of b.c.c. Fe. In all cases, no higher order magnetostrictive terms were detectable. With 15 to 20 atomic percent replacement of Fe by Ga, the magnetizations remain high ([M.sub.s] [nearly equals to] 1.8 T) and the magnetic anisotropies reduced ([K.sub.1] [nearly equals to] J/[m.sup.3]). Values of the `stiff' (high magnetic field) Young's modulus, Bulk modulus, Poison's ratio, and elastic constant [c.sub.11]-[c.sub.12] for [Fe.sub.85][Ga.sub.15] at room temperature are, respectively, 77 GPa, 111 GPa, 0.38, and 56 GPa. Index Terms--Actuator, Fe-Ga, Fe-Ga-Al, magnetostriction, structural materials, transduction.