Tb-Dy-Fe alloys are widely used in transducers, actuators and sensors due to the effective conversion between magnetic energy and mechanical energy (or acoustic energy).
1. Introduction
The physical effect of the magnetostriction of Tb-Dy-Fe alloys is utilized to realize their application in sensors, transducers and actuators through the conversion of magnetoelastic properties and mechanical energy.
Clark et al.
[1][2] discovered that the magnetization and magnetocrystalline anisotropy of composite rare-earth compounds composed of R′Fe
2 and R″Fe
2 (R′ and R″ denote different rare-earth elements) had a superposition effect. In particular, the λ
111 of pseudobinary Tb
xDy
1−xFe
2 compounds (0 < x < 1) could reach 1600–2400 × 10
−6, and the external magnetic field intensity required to achieve saturation magnetization was only 1.6 × 10
3 kA/m. Due to the large anisotropy of magnetostriction in the Tb-Dy-Fe single crystal, the magnetostrictive strain in the <111> easy axis is the largest. However, <111> is not the easy growth direction of the crystal. It is necessary to develop directional solidification technology to bring the grain orientation closer to the easy magnetization direction <111>
[3]. Tb-Dy-Fe alloys in <110> and <112> orientations are usually prepared by directional solidification
[4][5].
During the last years, many efforts have been dedicated to enhancing magnetostriction to reduce costs, such as alloying with other elements and improving the preparation process
[6][7][8][9]. In previous research, the partial substitution of Tb and Dy by Ho was investigated to reduce the magnetocrystalline anisotropy and effectively decrease the hysteresis
[10]. Some multicomponent alloys, such as (Tb
0.7Dy
0.3)
0.7Pr
0.3(Fe
1−xCo
x)
1.85 (0 ≤ x ≤ 0.6) and Tb
0.3Dy
0.7(Fe
1−xSi
x)
1.95 (x = 0.025), also presented good low-field magnetostriction performance
[10][11][12]. However, intrinsic brittleness and large eddy-current loss at high frequency still limit the application range of Tb-Dy-Fe alloys.
The magnetostriction of Tb-Dy-Fe alloys is related to the magnetocrystalline anisotropy of rare-earth compounds. It is also considered to be derived from the interaction between 4f electrons of rare-earth elements and 3d electrons of transition-metal ions
[13]. Since the (Tb, Dy)Fe
2 pseudobinary alloy system was proposed, there has been little effective progress in the understanding of its magnetostriction mechanism. To explore the great enhancement of its properties, an in-depth understanding of its physical nature is urgently needed. The concept and implication of the morphotropic phase boundary (MPB) have been introduced to the ferromagnetic material system, which provides a new perspective for the research of the magnetostrictive effect of Tb-Dy-Fe alloys and the development of high-performance magnetostrictive materials
[14][15][16]. Furthermore, the emergence and development of a new generation of synchrotron and light sources could more accurately detect the position change of atoms in the crystal, which would be conducive to the study of the magnetostriction mechanism of Tb-Dy-Fe alloys
[17][18].
2. Grain Orientation and Properties of Directionally Solidified Tb-Dy-Fe Alloys
In order to achieve the large magnetostriction of Tb-Dy-Fe compounds in a low magnetic field, directional solidification technology needs to be used to orient the grains in the easy magnetization direction as much as possible due to the anisotropy of magnetostriction.