Short-range magnetic order within the multiferroic erythrosiderite mineral(NH4)2FeCl5·H2O

Abstract

Molecular multiferroics are receiving a large amount of interest, in part due to the ease of synthesis and their potential for tuneability. An important compound within this field is ammonium pentachloroaquaferrate(III), ${({\mathrm{NH}}_{4})}_{2}{\mathrm{FeCl}}_{5}\ifmmode\cdot\else\textperiodcentered\fi{}{\mathrm{H}}_{2}\mathrm{O}$, which has received a lot of attention due to it having both magnetic and ferroelectric transitions at 7.3 and 6.9 K, respectively. The magnetic structure is complex, with many different exchange pathways; however, to date there has been no consideration of magnetic interactions above the critical temperature. Our paper utilizes muon spin spectroscopy, inelastic neutron scattering and quasielastic neutron scattering (QENS) to show that, as one might expect for these complex magnetic systems, there is indeed evidence for short-range order above 7.3 K and this persists up to $\ensuremath{\sim}15$ K. We also highlight the sensitivity of the QENS technique to the magnetic transition and any localized fluctuations.