Evolution of nematic and ferromagnetic ordering in suspensions of magnetic nanoplatelets

TL;DR

This study investigates how magnetic nanoplatelet suspensions develop nematic and ferromagnetic order, revealing that short-range magnetic and positional order exist at low concentrations and are influenced by dipolar interactions.

Contribution

It provides experimental evidence of magnetic and positional order evolution in nanoplatelet suspensions and introduces a simple model explaining ferromagnetic correlations.

Findings

Short-range order exists at low volume fractions.

Ferromagnetic contributions significantly influence nematic phase formation.

A simple model explains ferromagnetic correlations based on dipolar interactions.

Abstract

Suspensions of magnetic nanoplatelets in isotropic solvents are very interesting examples of ferrofluids. It has been shown that above a certain concentration {\Phi}NI such suspensions form a ferromagnetic nematic phase, which makes this system a unique example of a dipolar fluid. The formation of a nematic phase is driven by anisotropic electrostatic and long-range dipolar magnetic interactions. Here, we present studies of the evolution of short range positional and orientational magnetic order in the suspensions with volume fractions below and above {\Phi}NI, using small angle neutron scattering (SANS). The results show that in the absence of an external magnetic field, short range positional and orientational order already exist at relatively low volume fractions. Polarized SANS revealed that the contribution of ferromagnetic ordering to the formation of the nematic phase is significant. The ferromagnetic correlations can be qualitatively explained by a simple model, which takes into account anisotropic screened electrostatic and dipolar magnetic interactions.