Quantum Thermoactivation of Nanoscale Magnets

TL;DR

This paper analytically calculates the relaxation time for thermoactivated escape in a quantum spin system across all temperatures, revealing quantum effects like deep minima in activation rates due to level quantization.

Contribution

It provides an analytical solution for the relaxation time of quantum spins interacting with a boson bath, including quantum effects at low temperatures.

Findings

Deep minima in thermoactivation rate as a function of magnetic field.

Quantum level quantization influences escape rates at low temperatures.

Analytical expression valid across the entire temperature range.

Abstract

The integral relaxation time describing the thermoactivated escape of a uniaxial quantum spin system interacting with a boson bath is calculated analytically in the whole temperature range. For temperatures T much less than the barrier height \Delta U, the level quantization near the top of the barrier and the strong frequency dependence of the one-boson transition probability can lead to the regularly spaced deep minima of the thermoactivation rate as a function of the magnetic field applied along the z axis.