Abstract: We report a combined study using magnetization and Raman spectroscopy on the magnetic ionic liquid 1-ethyl-3-methylimidazolium tetrachloroferrate, Emim[FeCl4]. This material shows a long-range antiferromagnetic ordering below the Néel temperature TN ? 3.8 K. The effects of pressure on the magnetic properties have been studied using a miniature piston?cylinder CuBe pressure cell. This three-dimensional ordering is strongly influenced when hydrostatic pressure is applied. It is observed that low applied pressure is enough to modify the magnetic interactions, inducing a transition from antiferromagnetic to ferrimagnetic ordering. Raman spectroscopy measurements reveal important information about the existence of isolated [FeCl4]? anions and the absence of dimeric [Fe2Cl7]? units in the liquid and solid states. These features seem to suggest that the superexchange pathways responsible for the appearance of magnetic ordering are mediated through Fe-Cl?Cl-Fe. Furthermore, the liquid?solid phase transition exhibits a magnetic hysteresis near room temperature, which can be tuned by weak pressures.

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