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The single-molecule magnet (SMM) properties of a series of ferrocenium complexes, [Fe(η 5 -C 5 R 5 ) 2 ] + (R=Me, Bn), are reported. In the presence of an applied dc field, the slow dynamics of the magnetization in [Fe(η 5 -C 5 Me 5 ) 2 ]BAr F are revealed. Multireference quantum mechanical calculations show a large energy difference between the ground and first excited states, excluding the commonly invoked, thermally activated (Orbach-like) mechanism of relaxation. In contrast, a detailed analysis of the relaxation time highlights that both direct and Raman processes are responsible for the SMM properties. Similarly, the bulky ferrocenium complexes, [Fe(η 5 -C 5 Bn 5 ) 2 ]BF 4 and [Fe(η 5 -C 5 Bn 5 ) 2 ]PF 6 , also exhibit magnetization slow dynamics, however an additional relaxation process is clearly detected for these analogous systems., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)