Enhanced Coercivity in Ferrimagnetic [Fe(tren)(ea)][Fe2Se3]2 Through Coupling of Mixed-Valent [Fe2Se3]1– Double Chains and Trigonal Bipyramidal Fe Complexes

Abstract

Inorganic–organic hybrid compound, [Fe(tren)(ea)][Fe2Se3]2 (tren = tris(2-aminoethyl)amine C6H18N4; ea = ethanolamine, C2H7NO) has been synthesized by a solvothermal reaction using stoichiometric tren and excessive ea. The compound comprises mixed-valent [Fe2Se3]1– double chains and trigonal bipyramidal (TBP) [Fe(tren)(ea)]2+ complexes. This is the first report of Fe–Se hybrid materials with interstitial Fe-amine complexes in TBP geometry. Low-field magnetic measurements reveal a bifurcation between the field-cooled and zero-field-cooled magnetization curves at 26 K. Measurements under AC applied field show frequency-dependent peaks in the in-phase part of magnetic susceptibility, indicating the system behaves as cluster spin glass. Nevertheless, under applied field of 2 T, heat capacity measurements show a peak at 24 K, suggesting transition to a long-range magnetically ordered state. The moderately negative Weiss constant, θw = – 52(1) K, is indicative of antiferromagnetic nearest–neighbor interactions within the chains. The isothermal magnetization curve displays a multistep hysteresis loop due to a potential spin-reorientation transition, with a high coercivity of approximately 0.75 T. X-ray absorption spectroscopy confirms the mixed-valent nature of the [Fe2Se3] double chains. The 57Fe Mössbauer spectroscopy reveals complex magnetic ordering in [Fe2Se3] chains at 6 K. Additionally, magnetic splitting of the signal emerging from the [Fe(tren)(ea)]2+ complex is observed, indicating magnetic interactions between complexes and chains. This hypothesis was confirmed by a comparative DFT analysis of the reported compound and a hypothetical [Zn(tren)(ea)][Fe2Se3]2, which features nonmagnetic ions in the complex.