Magnetic properties of icosahedral alloys: The case of ${\mathrm{Al}}_{65}$${\mathrm{Cu}}_{20}$${\mathrm{Fe}}_{15}$

Various magnetic properties of a novel, thermodynamically stable, icosahedral alloy ${\mathrm{Al}}_{65}$ ${\mathrm{Cu}}_{20}$ ${\mathrm{Fe}}_{15}$, have been studied at low temperatures with ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ Mössbauer spectroscopy and ac susceptibility. It is found that Fe atoms bear no magnetic moment down to 1.5 K. The presence of a multiplicity of Fe sites in this alloy is demonstrated. It is argued that this reflects the intrinsic disorder in this system. The analysis of Mössbauer spectra of icosahedral alloys used in the literature in terms of two doublets or singlets with unphysically broad lines is shown to be incorrect, and consequently the assertion based on such analysis of there being two distinct transition-metal sites is unfounded. A critical review of published experimental data on the magnetic properties of icosahedral alloys has been performed. Arguments are presented which indicate that the presence or absence of local magnetic moments on transition metals in icosahedral alloys results from the intrinsic disorder rather than from icosahedral symmetry.