Effect of boron on structure and magnetic properties of magnetostrictive compound Dy0.7Pr0.3Fe2

Abstract

Crystal structure, magnetic properties and magnetostriction of Dy0.7Pr0.3(Fe1−xBx)2 (0⩽x⩽0.20) have been investigated by means of x-ray diffraction, ac initial susceptibility, a vibrating sample magnetometer, and a standard strain technique. The matrix of Dy0.7Pr0.3Fe2 alloy consists of (Dy,Pr)Fe2 phase with a cubic MgCu2-type structure and some amount of (Dy,Pr)Fe3 phase with a rhombohedral PuNi3-type structure. The introduction of boron effectively restrains the emergence of the iron-rich phase and thus decreases the amount of (Dy,Pr)Fe3 phase. Dy0.7Pr0.3(Fe1−xBx)2 alloy with x=0.05 contains small amount of (Dy,Pr)(Fe,B)3 phase, and those with x=0.10 and x=0.15 are essentially of a single (Dy,Pr)(Fe,B)2 phase. An unidentified minor phase appears when x=0.20. The lattice parameter of (Dy,Pr)(Fe,B)2 phase decreases monotonically with the boron substitution up to x=0.20, indicating that the boron atoms occupy the substitutional sites. The Curie temperature for (Dy,Pr)(Fe,B)2 phase obviously increases compared with the boron free one. The saturation magnetization at room temperature increases with increasing boron content for the alloys studied, suggesting that the partial boron substitution is beneficial to the increment of the exchange interactions in the Dy0.7Pr0.3Fe2 system. The increment of the magnetization originates from the decrement of iron content, because the Fe moment that aligns antiparallel with the Dy moment almost keeps constant in this system. Boron substitution for iron increases the lattice distortion and anisotropy, thus causes the decrease of the linear magnetostriction λa=λ∥−λ⊥ at the room temperature.