Size-induced transition from non–Griffiths-like to Griffiths-like clustered phase above the Curie temperature

Hefei National Laboratory for Physical Sciences at Microscale, University of Science and Technology of China Hefei, Anhui 230026, PRC

^a zhousm@ustc.edu.cn
^b shil@ustc.edu.cn

Received: 27 March 2012
Accepted: 11 May 2012

Abstract

Recent studies on several pervoskite oxides such as Sm_0.5Sr_0.5MnO₃, La_0.7Sr_0.3CoO₃, and La₂NiMnO₆, reveal that their inverse susceptibilities exhibit an upward deviation from Curie-Weiss behavior above T_C, indicating the existence of a non–Griffiths-like clustered phase due to the dominance of antiferromagnetic interactions in this regime. Here, we study the magnetic behaviors of their nanoparticles and find that the deviation becomes sharply downward, which is a typical characteristic of a Griffiths-like phase. This suggests that reducing the particle size induces a phase transition from non–Griffiths-like to Griffiths-like. We propose that the weakening of the antiferromagnetic interactions by size reduction is responsible for this transition.