Structural and magnetoelastic properties of non-stoichiometric TbFe2Mnx Laves phase

Abstract

In this paper, we studied TbFe2Mnx 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 TbFe2Mnx compounds are formed up to Mn concentration x = 0.25. The non-stoichiometric TbFe2Mnx compounds possess huge spontaneous magnetostriction in [111] direction (up to 2550 ppm) which result to distortion cubic MgCu2-type structure to rhombohedral (R3¯m) at room temperature. The formation of non-stoichiometric TbFe2Mnx compounds results from partial substitution of Tb by Mn in (6c) positions. It was found a characteristic value for the cubic MgCu2-type lattice parameter ac ≈ 7.2 Å. If binary RT2 (R is a rare-earth metal, T – 3d 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 RT2Mnx compounds. The Mn doping in TbFe2Mn0.25 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 TbFe2. It also preserve large magnetostriction at room temperature (λ|| ≈ 1530 ppm in magnetic field 18 kOe). This make non-stoichiometric TbFe2Mn0.25 compound promising material for various magnetostrictive applications in wide temperature range.