Role of short-range magnetic interaction between core and surface spins in exchange bias and memory effect in nanocrystalline doped manganite

Abstract

• Synthesis of bulk and nanocrystalline La 0.4 (Ca 0.5 Sr 0.5 ) 0.6 MnO 3 compounds. • Enhancement of ferromagnetic clusters in core part with size reduction is noticed. • Magnetic inhomogeneity induced glassy magnetic phase is observed in nanomaterial. • Magnetic disorder results in strong memory and exchange bias effect in nanocrystal. • Theoretical model for core-shell structure corroborates the short-range correlation. A comparative study of low temperature magnetic properties for bulk and nanocrystalline La 0.4 (Ca 0.5 Sr 0.5 ) 0.6 MnO 3 compounds has been presented here. Considerable enhancement of exchange bias as well as magnetic memory effect in nanocrystalline material has been observed compared to bulk. Substantial increase of ‘A’ -site size-disorder parameter ( σ 2 ) with ‘Sr’ doping concentration in La 0.4 Ca 0.6 MnO 3 compound is found to assist in destabilizing the charge ordering state along with a grow of ferromagnetic clusters in these systems. In nanomaterial, the short-range magnetic interaction between the increased ferromagnetic cluster and the antiferromagnetic matrix in the core part of the core-shell structure assists to develop strong magnetic disorder (glassy phase) in the system. Additionally, the magnetic interaction of uncompensated shell spins and its interaction with adjacent core ferromagnetic clusters also attribute to grow glassy phase in the system, resulting in strong memory effect and exchange bias effect. The experimental findings have been described in terms of different theoretical models developed for core-shell structure.