Exceptional combination of large magnetostriction, low hysteresis and wide working temperature range in (1-x)TbFe₂-xDyCo₂ alloys

Magnetostrictive materials with large magnetostriction, low hysteresis and wide working temperature range are desired for applications, but rarely obtained so far. In this work, we report a surprising finding in (1-x)TbFe₂-xDyCo₂ alloys: the composition of x = 0.5 exhibits a low hysteretic magnetostriction, λ_||,max ∼2066 ppm, which is 1.59 times as large as that of the commercial giant magnetostrictive alloy of Terfenol-D, λ_||,max ∼1298 ppm. Moreover, its temperature range for λ_|| >1298 ppm is even larger than 240 K, and another working temperature window for λ_|| >1000 ppm is from 40 K to 324 K, which can cover a large temperature fluctuation in space environments (e.g. 120-290 K in Mars). The established phase diagram of (1-x)TbFe₂-xDyCo₂ by systematic studies of magnetic susceptibility, X-ray diffraction and convergent-beam electron diffraction results, shows an emergence of morphotropic phase boundary (MPB) between rhombohedral (R) and orthorhombic (O) ferromagnetic phases, which is different from the MPB between R and T (tetragonal) phases in (1-y)TbFe₂-yDyFe₂. We reveal that the exceptional combination of giant magnetostriction, low hysteresis and wide working temperature range is caused by this R-O MPB. The comparison between R-O MPB and R-T MPB further shows the O phase plays a vital role in the property enhancement of R-O MPB composition. Our work indicates the construction of R-O MPB may provide a new way to find high-performance magnetostrictive materials.