Structural analysis and magnetic properties of lattice distortions from hexagonal to tetragonal systems in non-equilibrium Y–Fe alloys

Abstract

A structural analysis model, which was specialized by space group Immm and denoted by substituting a pair of iron atoms (iron dumbbell) for rare-earth (R) elements continuously, was devised and used to treat continuous lattice distortions from hexagonal TbCu7 to tetragonal ThMn12 structures observed in non-equilibrium Y–Fe alloys. Trajectories of lattice distortions due to annealing, which were drawn on a map arranged in terms of axial ratios b∕c and b∕a, could be classified into four types according to composition ratio (T∕R) of the Y–Fe alloys. Especially, type-I distortion (with composition range of 11.5≤T∕R≤13.5) transformed from a hexagonal structure with b∕a∼1.002 to a tetragonal one with b∕a=1.000 via a structure with a large distortion, i.e., b∕a=1.008. Meanwhile, type-II distortion (with composition range of 10.5<T∕R<11.5) transformed from a hexagonal structure with b∕a∼1.001 to an orthorhombic one as close as possible to a tetragonal one. Moreover, the continuous-lattice-distortion model could bring geometric insights on structural stability and magnetic properties of not only the alloys but also previously recognized compounds with modulated-CaCu5 structures, which are configured by substituting iron dumbbells for R elements.