Formation, Stability and Magnetism of New Gd₃TAl₃Ge₂ Quaternary Compounds (T = Mn, Cu)

Abstract:

A study on the formation and stability of new quaternary compounds with the general chemical formula Gd₃TAl₃Ge₂ (T = Mn, Cu) has been undertaken by experimental investigations (SEM-EDX, DTA and XRD) and density functional theory (DFT) calculations. These compounds crystallize in the hexagonal Y₃NiAl₃Ge₂-type structure (hP9, P–62m, Z = 1) (an ordered, quaternary derivative of the ternary ZrNiAl or of the binary Fe₂P prototypes), with lattice parameters values a = 7.0239(2) Å and c = 4.2580(1) Å for Gd₃MnAl₃Ge₂ and a = 7.0434(1) Å and c = 4.2089(1) Å for Gd₃CuAl₃Ge₂. DTA suggests a peritectic reaction for the formation of these compounds (at 1245°C for Gd₃CuAl₃Ge₂). The existence and stability of these phases has been explained on the basis of DFT calculations, and a comparison of ground state properties of the studied compounds with the earlier known Gd₃CoAl₃Ge₂ phase is outlined. The negative formation energies in all three cases govern the stability of compounds from theory as well, predicting Gd₃MnAl₃Ge₂ as the most stable phase with highest formation energy (–13.01 eV/f.u.). The total DOS are generic in nature and suggest the robust magnetism, with the Gd-f moments of ≈7 μ_B. An antiparallel coupling among Gd-f and T-d states is observed for all compounds, as usually seen in rare earth (R) - transition metal (T) compounds. Preliminary magnetization measurements on Gd₃MnAl₃Ge₂ show two ferromagnetic/ferrimagnetic (FM/FIM) like transitions at T_C1 = 142 K and T_C2 = 97 K, with another anomaly seen at ≈15 K. Isothermal magnetization data show no hysteresis even at 5 K, and the magnetization does not saturate up to 50 kOe, further suggesting a possible FIM behavior.

• Periodical: Solid State Phenomena (Volume 289)
• Pages: 93-101
• DOI: https://doi.org/10.4028/www.scientific.net/SSP.289.93
• Online since: April 2019
• Authors: Manish K. Kashyap, Timothy A. Hackett, Alessia Provino*, Arjun K. Pathak, Vitalij Pecharsky, Pietro Manfrinetti
• Keywords: Crystal Structure, DFT, Formation Energy, Gd₃TAl₃Ge₂, Magnetism, Quaternary Compounds, Rare Earth Intermetallics

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