Low Temperature Magnetic Ordering of the Magnetic Ionic Plastic Crystal, Choline[FeCl4]

We report on the nature of the low temperature magnetic ordering of a magnetic ionic plastic crystal, Choline[FeCl4]. This investigation was carried out using heat capacity measurements, neutron diffraction experiments and muon spin relaxation (mu SR) spectroscopy. The calorimetric measurements show the onset of an unusual magnetic ordering below 4 K with a possible second magnetic phase transition below 2 K. Low temperature neutron diffraction data reveal a three dimensional antiferromagnetic ordering at 2 K compatible with the previous magnetometry results. The analysis of mu SR spectra indicates a magnetic phase transition below 2.2 K. At 1.6 K, the analysis of the shape of the mu SR spectra suggests the existence of an additional magnetic phase with features of a possible incommensurate magnetic structure.