On the threshold of long-range magnetic order: UNi2/3Rh1/3Al study

Abstract

We present a study of magnetism of UNi2/3Rh1/3Al single crystals in comparison to UCoA1 and UNiAl. UCoA1 is an itinerant 5f-electron metamagnet with a critical field of metamagnetic transition Bc ≈ 0.6 T applied along the c-axis of the hexagonal ZrNiAl-type structure. The observed pressure and alloying effects on the ground state point to competing ferromagnetic and antiferromagnetic interactions to be responsible for the non-magnetic ground state. UNi2/3Rh1/3Al, a solid solution between an antiferromagnet (UNiAl) and a ferromagnet (URhAl), also shows a nonmagnetic ground state. The present study is devoted to find whether the non-magnetic ground state of UCoAl and UNi2/3Rhi1/3Al may be due to a similar underlying microscopic mechanism. Analysis of magnetic-filed induced effects in magnetization, specific heat and electrical resistivity reveals that the physics of UNi2/3Rh1/3Al is dominated by strong antiferromagnetic correlations persisting up to relatively high temperatures. The ground state can be understood in terms of frozen antiferromagnetically coupled U magnetic moments, Contrary, in UCoAl the ground-state U magnetic moment seems to be zero. The field-induced effects on properties of the two systems, although showing apparent analogies, are probably reflecting entirely different microscopic origin.