Structural and Magnetic Properties of Nonstoichiometric Tb0.27Dy0.73Fe1.9Mnx Compounds

Nonstoichiometric Tb0.27Dy0.73Fe1.9Mnx (0 ≤ x ≤ 0.25) alloys are synthesized, and their structural and magnetic properties are studied. Powder X-ray diffraction data allow us to find that, at x < 0.25, single-phase Tb0.27Dy0.73Fe1.9Mnx compounds with a rhombohedral TbFe2-type structure form; at x ≥ 0.25, a great amount of a phase with the Th6Mn23-type structure forms. The Tb0.27Dy0.73Fe1.9Mnx alloys are shown to be characterized by the giant spontaneous magnetostriction, which leads to the transformation of the cubic MgCu2-type crystal lattice into the rhombohedral TbFe2-type one. The increase in the manganese concentration in the nonstoichiometric compounds is shown to result in the decrease in the Curie temperature, increase in the spontaneous magnetostriction, and substantial increase in the coercivity at the liquid helium temperature (4.2 К).