Predicting Relaxation times of Single Molecule Magnets from First Principles

Single-Molecule Magnets (SMMs) are molecules which retain their magnetic moment in the absence of an external magnetic field. SMMs have been proposed as molecular candidates for information storage and processing technologies and are convenient testbeds for quantum computation experiments. The main limitation of SMMs is their low operational temperatures, currently reaching liquid nitrogen temperature for the best system. Spontaneous demagnetization is determined by a temperature dependent relaxation time, which limits the maximum operative conditions.

The development of a first-principles model for the prediction of demagnetization times is one of the long-term theoretical challenges in Molecular Magnetism. We present a methodology for the calculation of tunnelling demagnetization times (𝜏𝑄𝑇) and effective demagnetization barriers (Ueff) based on spin-spin dipolar induced quantum tunnelling [1]. Model performance was tested for 18 mononuclear, lanthanide SMMs, finding a good agreement between experiment and theory. Furthermore, non-trivial demagnetization pathways for three high-performance SMMs were predicted in accordance with literature references.

Our model correctly represents the enhancement of relaxation time upon magnetic dilution [2] and allows for the calculation of magnetic blocking temperatures [3], which is the main figure of merit determining SMM performance.

[1] D. Aravena, The Journal of Physical Chemistry Letters, 2018, 9, 5327.
[2] L. Llanos, D. Aravena, Journal of Magnetism and Magnetic Materials, 2019, 489, 165456
[3] A. Castro-Alvarez, Y. Gil, L. Llanos, D. Aravena, 2019, submitted