Short-Range Magnetic Ordered State Above T C in Double Perovskite Dy 2 NiMnO 6

Abstract

Magnetic properties of double perovskite Dy2NiMnO6 have been investigated by Raman spectroscopy and magnetometry. The temperature dependence of the symmetric stretching of the oxygen octahedra exhibits an anomalous softening, which is ascribed to the spin-phonon coupling. The significant softening extends up to 150 K, indicating the presence of short-range magnetic ordering above TC ∼ 95 K. The nature of this short-range magnetic ordered state is determined by a modified Curie-Weiss law, which is obtained with considering the effect of Dy3+ moments. It is found that the inverse susceptibility of bulk Dy2NiMnO6 exhibits an upward deviation from the modified Curie-Weiss behavior above TC, indicating the existence of a non-Griffiths-like phase. Furthermore, we study the magnetic behaviors of nanosized Dy2NiMnO6 and find that the deviation becomes downward, which is a typical characteristic of a Griffiths-like phase. This size-induced transition from a non-Griffiths-like phase to a Griffiths-like phase is well consistent with that reported in La2NiMnO6, which is proposed to originate from the weakening of the antiferromagnetic interactions by size reduction. Our results unify the nature of short-range magnetic ordered state above TC in double perovskite Re2NiMnO6 (Re = La, other rare earth) and suggest that the rare-earth moments may play substantial role in the magnetic properties of Re2NiMnO6 with magnetic Re ions.