A family of binary magnetic icosahedral quasicrystals based on rare earths and cadmium

Abstract

Examples of stable binary icosahedral quasicrystals are relatively rare, and at present there are no known examples featuring localized magnetic moments. These would represent an ideal model system for attaining a deeper understanding of the nature of magnetic interactions in aperiodic lattices. Here we report the discovery of a family of at least seven rare earth icosahedral binary quasicrystals, i-R-Cd (R = Gd to Tm, Y), six of which bear localized magnetic moments. Our work highlights the importance of carefully motivated searches through phase space and supports the proposal that, like icosahedral Sc12Zn88 (ref. ), binary quasicrystalline phases may well exist nearby known crystalline approximants, perhaps as peritectically forming compounds with very limited liquidus surfaces, offering very limited ranges of composition/temperature for primary solidification.

Crystal electric field excitations in the quasicrystal approximantTbCd6studied by inelastic neutron scattering

“…4,8,21,22 The starting elements (Tb: Ames Laboratory Material Preparation Center; Cd: 112 Cd from Cambridge Isotope Laboratories) were packed in a frit-disc crucible set 23 with a molar ratio Tb:Cd = 7:93, which were then sealed in a silica tube under partial Ar atmosphere. The ampoule was heated to 700 • C to realize a homogeneous liquid and slowly cooled to 500 • C over ∼ 130 hours.…”

“…The quasicrystal approximants, RCd 6 (R = rare earth), 2,3 and related icosahedral quasicrystal phases, i-R-Cd, 4 form a set of model systems to explore how magnetism evolves from a conventional periodic lattice (approximant phase) to an aperiodic quasicrystal. Although TbCd 6 manifests long-range antiferromagnetic order (T N ∼ 22 K), [5][6][7] only spin-glass-like behavior is observed in i-Tb-Cd with a spin freezing temperature of T F = 6 K. 4,8 In fact, all of the known quasicrystals with local moments exhibit spin-glass-like ground states at low temperature.…”

“…Although TbCd 6 manifests long-range antiferromagnetic order (T N ∼ 22 K), [5][6][7] only spin-glass-like behavior is observed in i-Tb-Cd with a spin freezing temperature of T F = 6 K. 4,8 In fact, all of the known quasicrystals with local moments exhibit spin-glass-like ground states at low temperature. 9,10 The origin of the differences in magnetic behavior between the periodic approximants and quasicrystalline phases remain an open and intriguing issue, especially in light of the fact that numerous theoretical studies have established that longrange magnetic order on a quasilattice is quite possible.…”

Use of frit-disc crucibles for routine and exploratory solution growth of single crystalline samples

“…The use of frit-disc crucibles was key to making the growth of 112 Cd and 114 Cd enriched samples possible. Figure 3 shows our newly determined, Cd-rich side of the Gd-Cd binary phase diagram [13,14]. In order to grow the related i-TbCd, we needed to use a melt with a starting ratio of Tb:Cd = 0.8:99.2.…”

“…The clean separation of crystalline phase from remaining solution allowed us to determine the composition of the liquid at the decanting temperature. By assessing the mass of either RCd 6 or i-RCd relative to the mass of decanted liquid and by varying decanting temperatures we were able to create the liquid-line [13,14]. Although this might be considered to be a rather time consuming method of determining the liquidus line, it is one of the most accurate since solution growth is really the ultimate test of how phases solidify out of solution.…”