Gd3Ni2 and Gd3CoxNi2−x: magnetism and unexpected Co/Ni crystallographic ordering. Issue 25 (9th June 2016)

• Record Type: Journal Article
• Authors: Provino, Alessia; Smetana, Volodymyr; Paudyal, Durga; Gschneidner, Karl A.; Mudring, Anja-Verena; Pecharsky, Vitalij K.; Manfrinetti, Pietro; Putti, Marina
• Is Part Of: Journal of materials chemistry. Volume 4:Issue 25(2016)
• Page Start: 6078
• Page End: 6089
• Publication Date: 2016-06-09
• Subjects: Materials -- Periodicals; Chemistry, Analytic -- Periodicals; Optical materials -- Research -- Periodicals; Electronics -- Materials -- Research -- Periodicals; 543.0284
• DOI: 10.1039/c6tc01035k
• Languages: English
• ISSNs: 2050-7526

Abstract

Abstract : The progressive increase of both the Pauli paramagnetic temperature ( θ P ) and the Curie temperature ( T C ) observed with the Co substitution at the 4i site on going from the binary Gd3 Ni2 to the ternary ordered Gd3 CoNi. Abstract : The crystal structure, composition and physical properties of Gd3 Ni2, which was earlier reported to exist in the Gd–Ni system without any details of its structure and properties, have been determined. This rare earth binary compound is a high-temperature phase: it forms via a peritectic reaction at 988 K (715 °C) and decomposes below ≈923 K (650 °C). The compound can be retained at room temperature as a metastable phase by quenching after high temperature annealing. Gd3 Ni2 crystallizes in the monoclinic Dy3 Ni2 structure type [ mS 20, C 2/ m (No. 12), Z = 4; with lattice parameters a = 13.418(3) Å, b = 3.720(1) Å, c = 9.640(2) Å, β = 106.250(3)°]. Ni can be substituted by Co up to 50% ( i.e. up to and including Gd3 CoNi) with no change in the structural prototype; the substitution of Co for Ni stabilizes the R3 Co x Ni2− x phases down to room temperature. The crystal structure, magnetic properties and magnetocaloric effect (MCE) have been investigated for both Gd3 Ni2 and the related Gd3 Co x Ni2− x solid solution alloys (0 ≤ x ≤ 1). The crystal structure of the Gd3 CoNi is a ternary ordered derivative of the monoclinic Dy3 Ni2 -type, where Co fully occupies only one of the two 4i Wyckoff sites available for the transition metal. To the best of our knowledge, this is the first example of an intermetallic phase showing ordered site occupations by the chemically quite similar elements Co and Ni. All compounds show long range ferromagnetic ordering, with T C progressively increasing from 147 K (for Gd3 Ni2 ) to 176 K (for Gd3 CoNi) as a cubic function of the Co content. Evidence of Co contributing to the magnetic interactions in these compounds has been found. First-principles total energy calculations predicted the ordered occupation of Co and Ni at the crystallographic sites of Gd3 CoNi, which was later confirmed by single crystal X-ray diffraction. The increased conduction electronic state (3d) exchange splitting at the Fermi level supports the experimentally observed enhanced Curie temperature in Gd3 CoNi compared to Gd3 Ni2 .