Magneto-structural study of phase pure $\alpha $ and $\beta $ type MnAs nanoparticles

There is extensive interest in understanding the properties of nanoscale materials that exhibit magneto-structural phase transitions because of their possible use in magnetocaloric applications. Bulk MnAs exhibits a ferromagnetic transition in the range 313-317 K, together with a structural transition from a hexagonal (\textit{$\alpha $}-MnAs) to an orthorhombic (\textit{$\beta $}-MnAs) lattice. We have studied the structural and magnetic properties of \textit{$\alpha $}-MnAs and\textit{ $\beta $}-MnAs nanoparticles synthesized using solution-phase arrested precipitation method. XRD and TEM studies show that both the \textit{$\alpha $} and\textit{ $\beta $} phase nanoparticles are crystalline, phase pure, and stable for weeks at room temperature. Magnetic measurements show that both the \textit{$\alpha $}-MnAs and \textit{$\beta $}-MnAs phase nanoparticles undergo ferromagnetic phase transitions near 315K, but we find no evidence for the associated \textit{$\alpha $} to \textit{$\beta $} structural transition seen in bulk MnAs. We will present an experimental investigation on the connection between structural and magnetic properties in \textit{$\alpha $} and\textit{ $\beta $} type MnAs nanoparticles, and discuss relevance to studies on other nanostructured systems.