Low-Temperature Crystal Structure and Mean-Field Modeling of ErxDy1−xAl2 Intermetallics

Yaroslav Mudryk,Vitalij K Pecharsky,Paula O Ribeiro,Bruno P Alho

doi:10.3390/met10121662

Abstract

Low-temperature crystal structure of the ErxDy1−xAl2 alloys with x = 0.45, 0.67, 0.90 was examined using temperature-dependent powder X-ray diffraction. The Er-rich sample, Er0.9Dy0.1Al2, exhibits a rhombohedral distortion associated with the magnetic ordering that occurs around 20 K. The rhombohedral distortion is suppressed in Er0.67Dy0.33Al2, while a weak low-temperature tetragonal distortion is observed in Er0.45Dy0.55Al2. The mean-field theory supports the correlation between the type of structural distortion and the variable easy magnetization axis in ErxDy1−xAl2 intermetallics.

Highlights

The interactions between two or more elements containing 4f electrons is a fascinating topic [1,2,3]with potential practical importance for novel technologies such as magnetocaloric cooling [4,5,6].The sheer number of known and yet to be discovered intermetallic compounds containing 4f elements is enormous, and this broad family becomes nearly infinite when considering the ability to partially substitute one lanthanide element with another
In magnetic lanthanides with a non-zero orbital quantum number, L, the presence of spin-orbit coupling and site-dependent crystalline electric fields lead to the splitting of the 4f energy levels and their population by electrons creating unusually complex magnetic structures [10,11,12,13,14]
Er and Dy ions showed no signs of any structural transformation below its Curie temperature, TC, despite the first-order nature of spin reorientation transition observed below TC clearly evidenced by heat capacity data. Both ErCo2 and ErAl2 Laves phase compounds adopt as easy magnetization axis (EMA), and both undergo a rhombohedral distortion [24,26], while DyCo2 and DyAl2 are both reported to be tetragonal at low temperature [23,26]

Summary

Introduction

The interactions between two or more elements containing 4f electrons is a fascinating topic [1,2,3]. Er and Dy ions showed no signs of any structural transformation below its Curie temperature, TC , despite the first-order nature of spin reorientation transition observed below TC clearly evidenced by heat capacity data Both ErCo2 and ErAl2 Laves phase compounds adopt as EMA, and both undergo a rhombohedral distortion [24,26], while DyCo2 and DyAl2 are both reported to be tetragonal at low temperature [23,26]. The non-magnetic aluminum, on the other hand, does not bring itinerant magnetism to bear, and Erx Dy1−x Al2 compounds should, in principle, exhibit magnetostructural behavior that reflects fundamental interactions between the Er and Dy 4f orbitals With this in mind, we performed a temperature-dependent crystallographic study of the Erx Dy1−x Al2 compounds with x = 0.45, 0.67, and 0.90 in order to understand how the interactions between two magnetic rare-earth sublattices influence the low-temperature crystallography. We use the mean-field theory tested earlier on similar R’R”Al2 pseudobinary systems [33, 34] to explain how the low-temperature crystallographic behavior evolves with a composition by modeling how the EMAs of Er and Dy sublattices change as functions of temperature (T) and of Er concentration (x)

Experimental

Modeling

Results

Lattice parameters of Er

Easy Magnetization Axis as a Function of Composition

Conclusions