Experimental Upper Bound on Superradiance Emission from Mn12 Acetate

TL;DR

This study used a Josephson junction detector to search for electromagnetic radiation during magnetization avalanches in Mn12-Acetate, finding no significant radiation and setting an upper limit on emitted energy.

Contribution

The paper provides the first experimental upper bound on superradiance emission during magnetization avalanches in Mn12-Acetate using a Josephson junction detector.

Findings

No significant electromagnetic radiation detected during avalanches.

Radiation energy is less than 1 part in 10^4 of total energy.

Magnetization reversal is non-uniform across the sample.

Abstract

We used a Josephson junction as a radiation detector to look for evidence of the emission of electromagnetic radiation during magnetization avalanches in a crystal assembly of Mn_12-Acetate. The crystal assembly exhibits avalanches at several magnetic fields in the temperature range from 1.8 to 2.6 K with durations of the order of 1 ms. Although a recent study shows evidence of electromagnetic radiation bursts during these avalanches [J. Tejada, et al., Appl. Phys. Lett. {\bf 84}, 2373 (2004)], we were unable to detect any significant radiation at well-defined frequencies. A control experiment with external radiation pulses allows us to determine that the energy released as radiation during an avalanche is less than 1 part in 10^4 of the total energy released. In addition, our avalanche data indicates that the magnetization reversal process does not occur uniformly throughout the sample.