Anomalous specific heat and magnetic properties of TmxDy1-xAl2 (0 ≤ x ≤ 1)

Pathak, Arjun K.; Bonilla, C. M.; Paudyal, D.; Mudryk, Y.; Pecharsky, V. K.

doi:10.1016/j.jallcom.2018.09.365

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

Abstract

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.

Authors:

^[1]; Bonilla, C. M. ^[1]; Paudyal, D. ^[1];

^[1];

^[1]

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

Publication Date:: 2018-09-28

Research Org.:: Ames Lab., Ames, IA (United States)

Sponsoring Org.:: USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:: 1478989

Alternate Identifier(s):: OSTI ID: 1642286

Report Number(s):: IS-J-9785
Journal ID: ISSN 0925-8388; PII: S0925838818336302

Grant/Contract Number:: AC02-07CH11358

Resource Type:: Accepted Manuscript

Journal Name:: Journal of Alloys and Compounds

Additional Journal Information:: Journal Volume: 774; Journal Issue: C; Journal ID: ISSN 0925-8388

Publisher:: Elsevier

Country of Publication:: United States

Language:: English

Subject:: 36 MATERIALS SCIENCE; Specific heat; Rare earth; First-order-phase-transition; Lanthanoids

Citation Formats


                    Pathak, Arjun K., Bonilla, C. M., Paudyal, D., Mudryk, Y., and Pecharsky, V. K. Anomalous specific heat and magnetic properties of TmxDy1-xAl2 (0 ≤ x ≤ 1).  United States: N. p., 2018. 
Web.  doi:10.1016/j.jallcom.2018.09.365.

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                    Pathak, Arjun K., Bonilla, C. M., Paudyal, D., Mudryk, Y., & Pecharsky, V. K. Anomalous specific heat and magnetic properties of TmxDy1-xAl2 (0 ≤ x ≤ 1).  United States.  https://doi.org/10.1016/j.jallcom.2018.09.365

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                    Pathak, Arjun K., Bonilla, C. M., Paudyal, D., Mudryk, Y., and Pecharsky, V. K. Fri .  
"Anomalous specific heat and magnetic properties of TmxDy1-xAl2 (0 ≤ x ≤ 1)".  United States.  https://doi.org/10.1016/j.jallcom.2018.09.365.  https://www.osti.gov/servlets/purl/1478989.

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@article{osti_1478989,

  title        = {Anomalous specific heat and magnetic properties of TmxDy1-xAl2 (0 ≤ x ≤ 1)},

  author       = {Pathak, Arjun K. and Bonilla, C. M. and Paudyal, D. and Mudryk, Y. and Pecharsky, V. K.},

  abstractNote = {Here, we study crystal structure, phase transitions and magnetism of pseudo-binary TmxDy1-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, TC. 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 TC = 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 TC 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.},

  doi          = {10.1016/j.jallcom.2018.09.365},

  journal      = {Journal of Alloys and Compounds},

  number       = C,

  volume       = 774,

  place        = {United States},

  year         = {2018},

  month        = {9}

}

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Figures / Tables:

TABLE I: Lattice constants and magnetic parameters obtained for Tm_xDy_1-xAl₂ compounds.

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Title: Anomalous specific heat and magnetic properties of TmxDy1-xAl2 (0 ≤ x ≤ 1)

Abstract

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