Structural and magnetoelastic properties of non-stoichiometric TbFe2Mn Laves phase

In this paper, we studied TbFe ₂Mn _x alloys using x-ray powder diffraction, x-ray fluorescent analysis, differential scanning calorimetry, scanning electron microscopy, and magnetostriction measurements. It was established that single phase non-stoichiometric TbFe ₂Mn _x compounds are formed up to Mn concentration x = 0.25. The non-stoichiometric TbFe ₂Mn _x compounds possess huge spontaneous magnetostriction in [111] direction (up to 2550 ppm) which result to distortion cubic MgCu ₂-type structure to rhombohedral ( R 3 ¯ m ) at room temperature. The formation of non-stoichiometric TbFe ₂Mn _x compounds results from partial substitution of Tb by Mn in (6 c) positions. It was found a characteristic value for the cubic MgCu ₂ -type lattice parameter a _c ≈ 7.2 Å. If binary RT ₂ ( R is a rare-earth metal, T – 3 d transitional metal) compounds have lattice parameter smaller than 7.2 Å, we can expect large values of Mn concentration ( x > 0.4) in non-stoichiometric RT ₂Mn _x compounds. The Mn doping in TbFe ₂Mn _0.25 compound led to significant increase of magnetostriction at liquid nitrogen temperature ( λ _|| ≈ 2400 ppm in magnetic field 18 kOe) which is 25 % larger than that of initial TbFe ₂. It also preserve large magnetostriction at room temperature ( λ _|| ≈ 1530 ppm in magnetic field 18 kOe). This make non-stoichiometric TbFe ₂Mn _0.25 compound promising material for various magnetostrictive applications in wide temperature range.