Anomalous specific heat and magnetic properties of Tm_xDy_1-xAl₂ (0 ≤ x ≤ 1)

Journal Article · 27 September 2018 · Journal of Alloys and Compounds

DOI: https://doi.org/10.1016/j.jallcom.2018.09.365 · OSTI ID:1478989

Pathak, Arjun K.  ^[1]; Bonilla, C. M. ^[1]; Paudyal, D. ^[1]; Mudryk, Y.  ^[1]; Pecharsky, V. K.  ^[1]

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1. Ames Lab. and Iowa State Univ., Ames, IA (United States)

Here, we study crystal structure, phase transitions and magnetism of pseudo-binary Tm_xDy_1-xAl₂ (0 ≤ x ≤ 1) compounds using temperature dependent X-ray powder diffraction, specific heat and magnetization measurements, first principles, and model calculations. In low external magnetic fields, Dy-rich compounds undergo continuous, second-order phase transitions at the respective Curie temperatures, T_C. In contrast, the Tm-rich compounds exhibit discontinuous, first-order anomalies in the magnetically ordered states. These sharp transitions correlate with a substantial energy difference between the room temperature cubic and ground state rhombohedral structures of TmAl₂. A clear anomaly in the lattice parameter is observed at ~30 K for x = 0.5, which nearly coincides with T_C = 31.2 K. The effective quadrupolar moment of the lanthanides changes sign around x = 0.5, which leads to a nearly zero anisotropy constant and approximately spherical effective 4f charge densities, providing an explanation for the lack of structural distortions below T_C for x = 0.5. The calculations confirm [001] as the easy magnetization axis in the ground state tetragonal structure of DyAl₂, and reveal collapse of the orbital magnetic moment when the easy magnetization direction changes to [111]. Within the rhombohedral ground state of TmAl₂ [111] is the easy magnetization direction.

• Research Organization: Ames Laboratory (AMES), Ames, IA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
• Grant/Contract Number: AC02-07CH11358
• OSTI ID: 1478989
• Report Number(s): IS-J--9785; PII: S0925838818336302
• Journal Information: Journal of Alloys and Compounds, Journal Name: Journal of Alloys and Compounds Journal Issue: C Vol. 774; ISSN 0925-8388
• Publisher: ElsevierCopyright Statement
• Country of Publication: United States
• Language: English