Abrupt Transition between Thermally-Activated Relaxation and Quantum Tunneling in a Molecular Magnet

Abstract

We report Hall sensor measurements of the magnetic relaxation of Mn${}_{12}$ acetate as a function of magnetic field applied along the easy axis of magnetization. Data taken at a series of closely-spaced temperatures between 0.24 K and 1.4 K provide strong new evidence for an abrupt ``first-order'' transition between thermally-assisted relaxation and magnetic decay via quantum tunneling.

4 pages, including 7 figures