Structural, magnetic, and Mössbauer spectral study of the icosahedral quasicrystalZn77Fe7Sc16

Abstract

The structural, magnetic, and Mössbauer spectral properties of the icosahedral quasicrystal Zn 77 Fe 7 Sc 16 are reported. The thermodynamically stable quasicrystal Zn 77 Fe 7 Sc 16 has a primitive six-dimensional Bravais lattice at room temperature with a six-dimensional hypercubic lattice constant of 7.087͑1͒ Å. Based on dc magnetization measurements, no evidence is found for a transition to a ground state with long-range magnetic order in the temperature range between 2 and 300 K. The dc zero-field-cooled and field-cooled susceptibility data indicate that the studied quasicrystal is a spin glass with freezing temperature T f = 7.75͑2͒ K. This is further confirmed by observing aging effects through the dc zero-field-cooled magnetization and the thermoremanent magnetization time decays and by the analysis of the frequency dependence of T f using the Vogel-Fulcher law and the dynamic scaling behavior near T f . However, the observed increase in the thermoremanent magnetization with the magnetic field in the low-field regime is incompatible with the ultrametrically organized phase space of a canonical spin glass. The nature of the spin-glass state of the icosahedral quasicrystal Zn 77 Fe 7 Sc 16 is therefore fundamentally different from that of a canonical spin glass. The bimodal distribution of the electric quadrupole splitting and of the hyperfine magnetic field derived from Mössbauer spectra indicates the existence of two classes of Fe sites.

High-energy X-ray diffraction studies of i-Sc12Zn88

“…It is also useful to compare the peak widths obtained in the present study on the binary i-Sc 12 Zn 88 with previous measurements on ternary Zn-M-Sc icosahedral alloys. To this end, in Figure 5, we plot the data for the PD sample along with the peak widths obtained from powder diffraction measurements on Zn 77 Fe 7 Sc 16 by Al-Qadi et al [16]. Although these data do not show a clear systematic dependence on Q perp over the range of their measurement, the peak widths for Q perp 1 Å are comparable to the present study.…”

“…Q perp dependence of peak widths from the present study of the PD single-grain i-Sc12 Zn 88 (open squares: blue online) and the powder diffraction measurements of Al-Qadi et al (diamonds: green online)[16].…”

Magnetism in icosahedral quasicrystals: current status and open questions

“…A -dependence of the magnetic susceptibility was observed for both the quasicrystal and the closely related ScZn 6 1/1 cubic approximant, consistent with the presence of a pseudogap in the density of states at the Fermi energy [89]. With the introduction of 3d TM elements, however, Curie–Weiss-like paramagnetism is recovered with effective moments substantially larger than what was previously observed for the Al-based quasicrystals [90–92]. For the Sc- TM -Zn quasicrystals it is generally presumed that the TM substitutions occupy the Zn-sites in the structure.…”

“…A cusp in the dc susceptibility at = 7.2 K and splitting between the FC and ZFC curves again signals a SG-like transition. Later measurements on icosahedral quasicrystals with the same starting compositions found somewhat different values for the effective moment and of /Fe and ≈ 11 K [92], or /Fe and ≈ 3 K [93], but very similar values for (figure 9). The source of discrepancies in the measured values for the effective moment has not been identified although it was speculated that even small changes in composition may strongly affect the moment value as was noted for the Al-based magnetic quasicrystals [21].…”

“…A comprehensive set of structural and bulk property measurements on powder samples of the Sc-Fe-Zn quasicrystal was reported by Al-Qadi et al , including x-ray diffraction, dc and ac susceptibility, TRM decay and 57 Fe Mössbauer spectroscopy [92]. The powder diffraction peak widths were quite narrow indicating a high degree of structural order in these samples and, in particular, there was no visible dependence of the peak widths on the phason momentum, [94], indicating the absence of any significant frozen in phason strain [95].…”