Abstract
The pseudobinary MnxNi2Zn11–x γ-brass-type phases at low Mn dopant levels (x = 0.1–0.5) were investigated. Crystal structures were determined for the two loading compositions of x = 0.3 and 0.5. The structures were solved in the cubic space group of I43m and are described in close analogy to the Ni2Zn11 parent γ-brass that is based on the 26-atom cluster, consisting of inner tetrahedron (IT), outer tetrahedron (OT), octahedron (OH), and cuboctahedron (CO). The refined site occupancies of the MnxNi2Zn11–x (x = 0.3, 0.5) reveal that the cluster center, which is empty in the Ni2Zn11, shows a partial occupation by Zn, with a partial depletion of Zn at the IT sites. The OH sites show a mixed Zn/Mn occupation. The OT and CO sites remain intact with respect to Ni2Zn11. Magnetic properties were studied for the Mn0.3Ni2Zn10.7 composition. The temperature-dependent zero-field-cooled and field-cooled magnetization, the ac susceptibility, the M(H) hysteresis curves, the thermoremanent magnetization, and the memory effect demonstrate typical broken-ergodicity phenomena of a magnetically frustrated spin system below the spin freezing temperature Tf ≈ 16 K. The Mn0.3Ni2Zn10.7 γ-brass phase classifies as a spin glass, originating predominantly from the random distribution of diluted Mn moments on the octahedral partial structure.
Highlights
Complex metallic alloys (CMAs) are a class of intermetallic compounds that possess giant unit cells comprising from several tens up to many thousands of atoms arranged in welldefined atomic clusters of different polyhedral symmetry.[1,2] CMA structures possess various types of disorder, including configurational disorder due to a statistically varying orientation of a particular subcluster, chemical disorder, partial site occupation, and split occupation, where two neighboring sites are alternatively occupied because they are too close in space
On the basis of the space group, γ-brasses are divided into four families:[3] (1) I-cell-type γ-brasses with space group I43m form a body-centered cubic lattice with two identical 26-atom clusters in the unit cell, centered at the highly symmetric positions (0,0,0) and (1/2,1/2,1/2), (2) P-cell type with space group P43m adopt a CsCl structure composed of two different 26-atom clusters, (3) F-cell type with space group F43m form superstructures, and (4) R-cell type with space group R3m are rhombohedral
The phase purity of the samples was verified by powder X-ray diffraction (PXRD) and Rietveld refinement plots, confirming that the entire series of the MnxNi2Zn11−x (x = 0.1−0.5) compounds were single-phase, belonging to the γbrass-type phase I43m
Summary
Complex metallic alloys (CMAs) are a class of intermetallic compounds that possess giant unit cells comprising from several tens up to many thousands of atoms arranged in welldefined atomic clusters of different polyhedral symmetry.[1,2] CMA structures possess various types of disorder, including configurational disorder due to a statistically varying orientation of a particular subcluster, chemical (substitutional) disorder, partial site occupation (occupancy smaller than 1), and split occupation, where two neighboring sites are alternatively occupied because they are too close in space. The category of CMAs includes the family of γ-brasses, containing 52 atoms in the unit cell.[3] The structure of γ-brass-type phases is described in terms of a 26-atom cluster, made up of four successive shells. The I-cell and P-cell types are the most numerous ones, found in 24 binary alloy systems.[3]
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