Reanalysis of Multichannel Field-Induced Magnetic Relaxation in a Selected Series of Co(II) Complexes

This study investigates field-supported slow relaxation of magnetization in 48 diverse Co(II) compounds, encompassing 0D, 1D, and 2D systems with coordination numbers 4, 5, and 6. Using AC susceptometry, out-of-phase susceptibility (χ″) was analyzed as a function of frequency, temperature, and DC field. Deconvolution via an extended Debye model reveals three distinct relaxation components: low-frequency (τLF ≈ 1 s), intermediate-frequency (τIF ≈ 1 ms), and high-frequency (τHF ≈ 1 μs) modes. While most complexes follow standard thermal behavior, the research highlights anomalous reciprocating thermal behavior (RTB), where relaxation times unexpectedly shorten upon cooling. By utilizing ln(τ) vs. ln(T) plots, the study points to relaxation mechanisms based on the power law expressed as 1/τ = CTn, including Raman (typically n = 5–9), direct (n = 1, field dependent), phonon bottleneck (n = 2), RTB (n = −1), Orbach (possibly n > 9), and quantum tunneling (n = 0) processes. Findings indicate that the Orbach mechanism is less common than traditionally assumed and that the retrieved experimental barrier (Ueff) is often a fictitious parameter. This study provides a critical reanalysis of the magnetic properties of a selected set of Co(II) complexes, with focus on slow magnetic relaxation.