Field‐Induced Slow Magnetization Relaxation of a Tetrahedral S=2 FeIIS4‐Containing Complex

In the work described herein, the spin relaxation properties of the mononuclear tetrahedral S=2 [Fe{(SPiPr2)2N}2] complex (1) were studied by employing static and dynamic magnetic measurements at liquid helium temperatures. In the absence of an external direct current (DC) magnetic field, 1 exhibits fast magnetization relaxation. However, in the presence of external magnetic fields of a few kOe, slow relaxation is induced as monitored by alternating current (AC) magnetic susceptibility measurements up to 10 kHz, in the temperature range 2–5 K. Analysis of the temperature dependence of the corresponding relaxation time reveals contributions by Quantum Tunnelling of Magnetization, and the Direct and Orbach processes in the magnetization relaxation mechanism of 1. The energy barrier, Ueff, of the Orbach process, as determined by this analysis, is compared with that related to the zero‐field splitting parameters of 1 which were previously determined by high‐ frequency and ‐field electron paramagnetic resonance and Mössbauer spectroscopies. The mononuclear tetrahedral S=2 [Fe{(SPiPr2)2N}2] complex (1) exhibits slow magnetic relaxation in the presence of an external magnetic field, as monitored by Alternating Current (AC) magnetometry. The magnetization relaxation mechanism involves contributions from the Quantum Tunnelling of Magnetization and the Direct and Orbach processes. The energy barrier for the Orbach process relates to the zero‐field splitting of the S=2 Fe(II) complex 1.