Characterisation of magnetic relaxation on extremely long timescales

Abstract

Magnetisation decay measurements are commonly being used to characterise very slow relaxation in single-molecule magnets. We explore measurement protocol and data analysis to define the best practise.

AtomAccess: A Predictive Tool for Molecular Design and Its Application to the Targeted Synthesis of Dysprosium Single-Molecule Magnets

“…Upon doping in a diamagnetic host, the QTM rates of the CIP decrease, in accord with dipolar fields being critical for enabling QTM. The 17 (e ⟨lnτ⟩ = 363 s at 2 K), 69 which has a similarly acute Cp R centroid •••Dy•••Cp R centroid angle. Although the coordination of the WCA in the CIP promotes faster magnetic relaxation, it is noteworthy that the differences between the SMM behavior of the SIP and CIP in this work are relatively small compared to the more detrimental equatorial interactions seen for {Dy(Cp R ) 2 } + fragments previously described in the literature.…”

“…Complexes 3-Dy·C 6 H 6 and 4-Dy were further characterized using the “waveform” method of Hilgar et al, which employs a square wave magnetic field (0.18–28 mHz, ±8 Oe) around zero dc field. In- and out-of-phase susceptibilities were then extracted using CC-FIT2 , via a discrete Fourier transform (Supporting Information Section S9.3). Ac and waveform data were fit to the generalized Debye model or double generalized Debye model in CC-FIT2 to extract relaxation times (τ debye ) and distributions. , Magnetic relaxation at lower temperatures were characterized with dc magnetization decay measurements.…”

“…Some of us have recently shown that e ⟨lnτ⟩ extracted from stretched exponential fits to magnetization decays is the most accurate way of characterizing magnetic relaxation on long time scales, providing the best agreement with τ debye (Supporting Information Section S9.5). , Estimated standard deviations for ac, waveform, and dc data were derived from logarithmic relaxation times. , …”

Thermally Stable Terbium(II) and Dysprosium(II) Bis-amidinate Complexes

“… a Obtained from fitting ac and dc relaxation data with CC-FIT2 , using the equation τ − 1 = τ 0 − 1 exp false[ prefix− U eff / T false] + C T n + τ QTM − 1 to define the temperature dependence of the relaxation time τ –1 , where U eff is the effective barrier to magnetic reversal, τ 0 is the attempt time of the phonon bath, C and n define Raman relaxation, and τ QTM is the QTM time scale. b Crystalline samples. c Solution samples. d Parameter value was fixed during fitting. …”

“…The magnetic relaxation rates of 1-Ln, 2-Ln, and 3-Ln were probed by ac magnetic susceptibility and dc magnetization decay experiments. Ac data were fitted with a generalized Debye model, 27 and dc magnetization decay data were fitted with a stretched exponential model, both in CC-FIT2, 59,60 unless stated otherwise. The temperature dependence of magnetic relaxation in SMMs is generally described with the equation…”