Quantum Tunneling of Magnetization — QTM ’94, 1995 NATO Science Series E: Series, Vol. 301

The first NATO Advanced Workshop on Quantum Tunneling of Magnetization (QTM) was organized and co-directed by Bernard Barbara, Leon Gunther, Nicolas Garcia, and Anthony Leggett and was held from June, 27 through July 1, 1994 in Grenoble and Chichilianne, France. These Proceedings include twenty-nine articles that represent the contributions of the participants in the Workshop. Quantum Tunneling of Magnetization is not only interesting for purely academic reasons. It was pointed out in the review article by L. Gunther in the December, 1990 issue of Physics World, that QTM may be destined to play a significant role within the next two decades in limiting the density of information storage in magnetic systems. Recent advances have indicated that this limitation may well be reached even earlier than first predicted. Furthermore, the number of people who have entered the field of study of QTM during these past few years has increased many fi)ld. The time was therefore opportune to hold a Workshop to bring together for the first time the leading researchers of QTM, both theoretical and experimental, so as to discuss the current status of the field. The most controversial issue at the time of the Workshop was how to establish r.eliable criteria for determining whether experimental results do indeed reveal manifestations of QTM. We believe that much progress was made at the Workshop on this issue.

I. General Introduction.- “Macroscopic Quantum Effects in Magnetic Systems: An Overview”.- II. Particles (Theory).- “Theory of Mesoscopic Quantum Tunneling in Magnetism: A WKB Approach”.- “Quantum Spin-Tunneling: A Path Integral Approach”.- “Quantum Tunneling in Small Particles”.- “Macroscopic Quantum Tunneling in Ferromagnets, Antiferromagnets”.- “Monte-Carlo Simulations on Reversal Magnetization of Small Clusters”.- III. QTM in Magnetic Relaxation (Experiment).- “Quantum Tunneling of Magnetization”.- “Relaxation and Mesoscopic Quantum Tunneling of Magnetization in Amorphous Rare-Earth Alloys”.- “Linear Response and Thermal Equilibrium Noise of Magnetic Materials at Low Temperature: Logarithmic Relaxation, l/F Noise, Activation and Tunneling”.- “AC Susceptibility Relaxation Studies on a Manganese Organic Cluster Compound: Mn12Ac”.- “Evidence for Quantum Tunneling of the Magnetization in Mn12Ac”.- “Acoustic and Magnetic Properties of Rare-Earth-Ion-Doped Glasses: Elastic and Magnetic Tunneling States”.- “DC-Squid Magnetization Measurements of Single Magnetic Particles”.- IV. Macroscopic Coherence of Magnetization (Experiment).- “Macroscopic Quantum Tunneling of Magnetization in Natural and Artificially Engineered Ferritin”.- V. Quantum Tunneling of Domain Walls (Experiment).- “Domain Wall Tunneling in a One Dimensional Ferromagnet”.- VI. Dissipation in QTM (Theory).- “Nuclear Spin Dissipation in Magnetic Macroscopic Quantum Phenomena”.- “Macroscopic Quantum Tunneling and Dissipation of Domain Wall in Ferromagnetic Metals”.- “The Collective Coordinate Method and Bloch Wall Motion ”.- VII. Spin Parity Effects in QTM (Theory).- “Spin Parity Effects and Macroscopic Quantum Coherence of BlochWalls”.- “Spin Environments and the Suppression of Quantum Coherence”.- “Unconventional Environments”.- VIII. QTM & Electron-Electron Interactions (Theory).- “Particle Tunneling and ‘Magnetization Tunneling’ in the Presence of Electron-Electron Interaction”.- IX. Comments on Theory and Experiment.- “On the Search for Quantum Tunneling of Magnetization”.- X. Macroscopic Quantum Tunneling in Superconductors (Experiment).- “Quantum Tunneling of Vortices in High-Tc Superconductors: Magnetic Relaxation Experiments in T1BaCACuO Compounds”.- “Crossover From Thermal to Quantum Regime in Vortex Motion in Conventional Type II Superconductors: Slow Magnetic Relaxation and Abrupt Flux Jumps”.- “Flux Motion by Quantum Tunneling”.- “Macroscopic Quantum Tunneling in Long Josephson Junctions”.- XI. Quantum Computers (Theory).- “Quantum Computing and Spin Physics”.- XII. Scientific Summary of Workshop.