Cooperative ordering of superparamagnetic ZnO nanograins

TL;DR

This study investigates the magnetic behavior of ZnO nanoparticles, revealing cooperative magnetic ordering and intergrain interactions that suggest a transition from superparamagnetic to a more correlated magnetic state.

Contribution

It provides new insights into the magnetic interactions and ordering mechanisms in ZnO nanograins, supported by experimental data and modeling.

Findings

Magnetic hysteresis depends on cooling field in high-temperature annealed samples

Evidence of long-range intergrain magnetic interactions

Reduction of magnetization explained by vortex-like flux closure

Abstract

In this paper we have tried to understand the precise nature of magnetism in ZnO nanoparticles. Cooling field dependence of magnetic hysteresis and coercive field was observed for high temperature annealed sample indicating cooperative magnetic correlation and ordering within the agglomerated nanograins. The increasing induced internal magnetic field along the direction of external field for the high temperature annealed sample has been fitted with the modified Weiss-Brillouin model indicating emergence of long range intergrain interaction among the superparamagnetic grains. We propose a simple idea that explains the reduction of magnetisation due to vortex state like flux closure situation.