Superconductivity and magnetism in heavy-fermion UPd $_{2}$ (Al,Ga) $_{3}$

We present bulk properties (resistivity, specific heat, and susceptibility) of the quasiternary system UPd

_{2}

(Al

_{1 - x}

_{x})

_{3}

and derive the superconducting and magnetic phase diagrams. For low Ga substitution

(x <~ 0.25)

a complete suppression of superconductivity is found, while the magnetic properties are hardly affected. For larger

x

the magnetic transition temperature

T_{N}

gradually decreases, and the mass enhancement of the electrons increases, until at

x

=0.8–0.9 a crystallographic transition takes place from the PrNi

_{2}

_{3}

to the BaB

_{2}

_{3}

lattice. At the structural transition

T_{N}

discontinuously increases, while the electronic specific heat

γ

grows smoothly through the transition. We discuss the relationship between the alloying parameter

x

and the magnetic ordering and electronic hybridization, respectively. The strong suppression of the superconductivity in UPd

_{2}

_{3}

with Ga suggests an unconventional mechanism of superconductivity, most probably related to spin fluctuations mediating the pairing.

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Superconductivity and magnetism in heavy-fermion UPd2(Al,Ga)3