Magnetic Avalanches in Molecular Magnets

Abstract

Abstract. The reversal of the magnetization of crystals of molecular magnets that have a large spin and high anisotropy barrier generally proceeds below the blocking temperature by quantum tunneling. This is manifested as a series of controlled steps in the hysteresis loops at resonant values of the magnetic field where energy levels on opposite sides of the barrier cross. An abrupt reversal of the magnetic moment of the entire crystal can occur instead by a process commonly referred to as a magnetic avalanche, where the molecular spins reverse along a deflagration front that travels through the sample at subsonic speed. In this chapter, we review experimental results obtained to date for magnetic deflagration in molecular nanomagnets.

Magnetic Blocking at 10 K and a Dipolar-Mediated Avalanche in Salts of the Bis(η8-cyclooctatetraenide) Complex [Er(COT)2]−

“…Given evidence of a magnetic avalanche through dc relaxation measurements, we sought to determine whether this phenomenon was also contributing to the magnetization drop observed in variable-field measurements. The occurrence of a magnetic avalanche is proposed to be linked to dipolar interactions (cold deflagration), such that dilution of 1 alone might lead to opening of the hysteresis loop. However, as a stand-alone phenomenon, tunneling can lead to loss of remnant magnetization near zero field and be mediated by dipolar interactions .…”

Transformation of the coordination complex [Co(C3S5)2]2− from a molecular magnet to a potential qubit

“…3b , highlight the temperature independent regime below 3 K at zero dc field, owing to QTM 3 or possibly avalanche processes. 19 Above 3 K however, all compounds exhibit thermally activated relaxation, often attributed to two-phonon mediated Raman and Orbach spin relaxation processes, which impart a T n and exponential dependence on T for τ , respectively. 20 In order to understand the relative contributions of each pathway in 1–4 , we fit the temperature profiles of τ to account for QTM, Raman, and Orbach relaxation according to the equation, τ –1 = ν QTM + BT n + τ 0 –1 e U eff / kT .…”

A Mononuclear Transition Metal Single-Molecule Magnet in a Nuclear Spin-Free Ligand Environment

“…Analysis of the temperature dependence of τ was conducted to determine the process responsible for the slow magnetic relaxation . Notably, relaxation via quantum tunneling or avalanche mechanisms can provide temperature-independent relaxation times, which are observed in 1 below 3 K. Above 3 K, however, τ is highly temperature dependent. In mononuclear SMMs, such temperature dependence is most often correlated to Raman and Orbach spin reversal processes.…”