RESUMO
We discovered a ferromagnetic Au-Ga-Dy icosahedral quasicrystal (i QC), not only with high phase purity but also with tunable composition. The isothermal magnetization of the polycrystalline ferromagnetic i QC was closely investigated and the mean-field-like nature of the ferromagnetic transition is elucidated. Moreover, the maximum Weiss temperature (θ_{p}) of the i QCs was found at the electrons-per-atom (e/a) ratio of 1.70 being well consistent with those of ACs, validating tunability of the magnetic properties of i QCs on the basis of θ_{p}-e/a scheme for the first time. Thus, the present work provided direct evidence that the magnetism of the i QCs depends on the e/a ratio or the Fermi energy, paving the way for future studies on various exotic magnetic textures formed on a quasiperiodic lattice through the e/a ratio.
RESUMO
The magnetic susceptibility of the 1/1 approximants to icosahedral quasicrystals in a series of Cd85-xMgxTb15 (x = 5, 10, 15, 20) alloys was investigated in detail. The occurrence of antiferromagnetic to spin-glass-like transition was noticed by increasing Mg. Transmission electron microscopy analysis evidenced a correlation between the magnetic transition and suppression of the monoclinic superlattice ordering with respect to the orientation of the Cd4 tetrahedron at T > 100 K. The possible origins of this phenomenon were discussed in detail. The occurrence of the antiferromagnetic to spin-glass-like magnetic transition is associated with the combination of chemical disorder due to a randomized substitution of Cd with Mg and the orientational disorder of the Cd4 tetrahedra.
RESUMO
A systematic investigation has been performed to elucidate effects of rare earth type and structural complexity on magnetic properties of icosahedral quasicrystal (iQC) and their cubic approximants (APs) in the ternary Cd-Mg-RE (RE = Gd, Tb, Dy, Ho, Er, and Tm) systems. At low temperatures, iQCs and 2/1 APs exhibit spin-glass-like freezing for RE = Gd, Tb, Dy, and Ho, while for Er and Tm they do not show freezing behavior down to the base temperature â¼2 K. The 1/1 APs exhibit either spin-glass-like freezing or antiferromagnetic (AFM) ordering depending on their constituent Mg content. The T f values show increasing trend from iQC to 2/1 and 1/1 APs. In contrast, the absolute values of Weiss temperature for iQCs are larger than those in 2/1 and 1/1 APs, indicating that the total AFM interactions between the neighboring spins are larger in aperiodic, rather than periodic systems. Competing spin interactions originating from the long-range Ruderman-Kittel-Kasuya-Yoshida mechanism along with chemical disorder of Cd/Mg ions presumably account for the observed spin-glass-like behavior in Cd-Mg-RE iQCs and APs.