Abstract
The magneto–elastic coupling effect correlates to the changes of moment and lattice upon magnetic phase transition. Here, we report that, in the pseudo-binary Laves-phase Tb1-xDyxCo2 system (x = 0.0, 0.7, and 1.0), thermal expansion and magnetostriction can probe the ferrimagnetic transitions from cubic to rhombohedral phase (in TbCo2), from cubic to tetragonal phase (in DyCo2), and from cubic to rhombohedral then to tetragonal phase (in Tb0.3Dy0.7Co2). Furthermore, a Landau polynomial approach is employed to qualitatively investigate the thermal expansion upon the paramagnetic (cubic) to ferrimagnetic (rhombohedral or tetragonal) transition, and the calculated thermal expansion curves agree with the experimental curves. Our work illustrates the correlation between crystal symmetry, magnetostriction, and thermal expansion in ferrimagnetic Laves-phase alloys and provides a new perspective to investigate ferrimagnetic transitions.
Highlights
Magnetic transition is the physical fundamental for magnetism and magnetic materials [1,2]
In this work, exemplified with the Laves-phase Tb1-x Dyx Co2 compounds, the paramagnetic–ferrimagnetic and ferrimagnetic–ferrimagnetic transitions in view of structural transition, and the correlation between thermal expansion, magnetostriction, and the structural transition are demonstrated for the first time
In order to avoid the measurement error caused by the strain gauge itself with temperature variation, the thermal expansion was measured twice for each sample: Without magnetic field (0 Tesla) and with magnetic field (1 Tesla), and the thermal expansion versus temperature curves used for detecting the transition are obtained from the subtraction of the two
Summary
Magnetic transition is the physical fundamental for magnetism and magnetic materials [1,2]. Since the moments of the rare-earth elements and the cobalt are antiparallel, the Laves-phase intermetallic RT2 compounds (R, rare-earth element; T, transition metal element, Fe/Co/Ni) are ferrimagnetic below Curie temperature (TC ) [1,5]. The Laves-phase RCo2 compounds, except the GdCo2 , for which the Curie temperature (TC ) is above 300 K, demonstrate paramagnetic–ferrimagnetic transition. Materials 2019, 12, 1755 below 300 K, allowing the convenience of investigation from paramagnetic to ferrimagnetic states [10] It has been extensively studied and well known that the distortion of the rare earth-based intermetallic compounds accompanying the change of the magnetic ordering (magnetic transition) is attributed to the interaction between the rare earth and the transition metals [8,10,11,12,14,15,16]. In this work, exemplified with the Laves-phase Tb1-x Dyx Co2 compounds, the paramagnetic–ferrimagnetic and ferrimagnetic–ferrimagnetic transitions in view of structural transition, and the correlation between thermal expansion, magnetostriction, and the structural transition are demonstrated for the first time
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