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要旨

In the antiferromagnetic heavy-fermion compound U2Zn17, the Sommerfeld coefficient. can be enhanced if all Zn atoms are replaced by a combination of Cu and Al or Cu and Ga. In the former ternary phase, glassy behavior was observed, while for the latter, conflicting ground-state reports suggest material quality issues. In this work, we investigate the U2Cu17-xGax substitutional series for 4.5 <= x <= 9.5. In the homogeneity range of the phase with the Th2Zn17-type of crystal structure, all samples exhibit glassy behavior with 0.6 K <= T-f <= 1.8 K. The value of the electronic specific heat coefficient gamma in this system exceeds 900 mJ/mol(U) K-2. Such a drastic effective-mass enhancement can possibly be attributed to the effects of structural disorder, since the role of electron concentration and lattice compression is likely minimal. Crystallographic disorder is also responsible for the emergence of non-Fermi-liquid behavior in these spin-glass materials, as evidenced by logarithmic divergence of magnetic susceptibility, specific heat, and electrical resistivity.