Ferromagnetic ordering in UFe_0.5Ni_0.5Al

Abstract

The alloy UFe 0:5 Ni 0:5 Al crystallizing in the hexagonal ZrNiAl-type structure has been studied by means of neutron powder diffraction and specific heat measurements. The Ni atoms occupy preferentially the (1b) sites. The transition into a ferromagnetic state at T C $ 55 K reported previously is corroborated by the occurrence of specific heat anomaly and magnetic reflections. The magnetic structure consists of the ferromagnetic (001)-planes with the magnetic moments parallel to the c-axis. At 1.4 K, the ordered uranium moment is about 0.6 m B . The low-temperature dependence of C p may be described by an expression involving an energy gap in the magnon spectrum. The electronic coefficient of the specific heat is modestly enhanced and amounts to about 47 mJ/mol K 2 . This feature together with a small value of m ord point to the strongly 5f-d hybridized character of the magnetism in UFe 0:5 Ni 0:5 Al.