Dual disorder-driven magnetic dynamics in GdCu2 superantiferromagnetic nanoparticles

Abstract

The spin dynamics in magnetically disordered GdCu2 nanoparticles, varying the nanoparticle size in the range 53 to 7 nm, has been scrutinized. Dynamic χAC susceptibility measurements have revealed the existence of dissipation at Tg = 18 K, which is associated to the spin freezing transition, for all the ensembles. Besides, the superantiferromagnetic ensembles (〈D〉≥ 24 nm) also showcase a dissipation contribution close to the vicinity of the Néel transition, TN = 40.2 K. This dissipation, which takes the form of two humps located at Td1 = 33.5(5) K and Td2 = 40.0(5) K, is associated to uncompensated antiferromagnetic moments. Time-dependent phenomena (ageing and memory effects) are only evidenced below the spin freezing transition, evidencing that solely this low-temperature disordered phase is driven by the frustration of RKKY exchange interactions. Consequently, GdCu2 nanoparticles display a dual disorder-driven magnetic dynamics, which are the one ascribed to the magnetically frustrated moments located at the nanoparticle surface; and that of uncompensated antiferromagnetic moments located within the nanoparticle core.