Magnetic clusters on the verge of long range ferromagnetism in Lu(Fe0.75Al0.25)(2) and Lu(Fe0.50Al0.50)(2) alloys.

Lu(Fe0.75Al0.25)(2) and Lu(Fe0.50Al0.50)(2) alloys have been produced by arc-melting. DC and AC magnetization, Mossbauer spectroscopy, specific heat and neutron diffraction experiments have been performed to determine their magnetic ground state. DC magnetization curves measured at low fields (H < 1 kOe) evidence two peaks, at T-SRO and T-f, and magnetic irreversibility. The peak at T-SRO vanishes and the one at T-f smears out when high fields (H > 1 kOe) are applied. The thermal variation of AC susceptibility shows that both transitions at T-SRO and T-f are frequency dependent. Neither magnetic splitting nor broadening is observed in the Mossbauer spectra of both compounds in the T-f < T < T-SRO thermal range. A magnetically split spectrum is only observed in Lu(Fe0.75Al0.25)(2) for T < T-f. The absence of long range ferromagnetic order in both alloys is confirmed by specific heat and neutron diffraction measurements. The overall interpretation points to a clustered magnetic environment due to the random positions of Fe atoms in the crystallographic cell. At T-SRO a short range ferromagnetic order takes place within the clusters, which become frustrated at T-f, when the random anisotropy of the clusters enables their freezing. (C) 2016 Elsevier B.V. All rights reserved.