Wydział Chemii

Roman Boča

Alina Bieńko

Jan Titiš

Cyril Rajnák

2026

Magnetochemistry

12

109/1-109/44

10.3390/magnetochemistry12100109

Naukowa

Angielski

Artykuł

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 (τ_LF ≈ 1 s), intermediate-frequency (τ_IF ≈ 1 ms), and high-frequency (τ_HF ≈ 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 (U_eff) 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.

Co(II) complexes, slow magnetic relaxation, AC susceptibility, relaxation mechanisms

CC-BY

http://dx.doi.org/10.3390/magnetochemistry12100109

http://www.mdpi.com/journal/metals