Abrupt crossover between thermally activated relaxation and quantum tunneling in a molecular magnet

¹ Physics Department, City College of the City University of New York New York, NY 10031, USA
² Department of Condensed Mater Physics, The Weizmann Institute of Science Rehovot 76100, Israel
³ Department of Chemistry and Biochemistry, University of California at San Diego La Jolla, CA 92093, USA
⁴ Department of Chemistry, Indiana University - Bloomington, Indiana 47405, USA

Received: 22 May 2001
Accepted: 27 June 2001

Abstract

We report Hall sensor measurements of the magnetic relaxation of Mn₁₂ acetate as a function of magnetic field applied along the easy axis of magnetization. Detailed data taken at a series of closely spaced temperatures between 0.24 K and 1.4 K indicate an abrupt shift between thermally activated and ground-state tunneling over a narrow range of temperature.