Macroscopic Quantum Tunneling of the Magnetic Moment

Abstract

This is the first book presenting a coherent theoretical and experimental treatment of the rapidly developing field of macroscopic quantum tunneling of the magnetic moment. The theory is based on the concept of the magnetic instanton and its renormalization by the dissipative environment. The book includes discussions of the tunneling of magnetic moment in small ferromagnetic grains, tunneling of the Ne'el vector in antiferromagnetic grains, quantum nucleation of magnetic domains, and quantum depinning of domain walls. The experimental part collects the majority of recent data that are, or may be, relevant to spin tunneling. Among the topics described are low temperature magnetic relaxation and its interpretation in various systems, experiments on single particles and mesoscopic wires, and resonant spin tunneling in molecular magnets. This study of an important new field in condensed matter physics by two leading contributors to the subject will be of interest to theorists and experimentalists alike.

Effects of quantum mechanics on the deflagration threshold in the molecular magnetMn12acetate

“…The magnetic properties of the Mn 12 -Ac single crystals were found to be similar to those previously published. 4,6,[14][15][16] We used a relatively large crystal of Mn 12 -Ac that was about 2 mm long and 0.5 mm wide. Smaller crystals did not show magnetic avalanches on sweeping the magnetic field due to rapid escape of heat through the surface ͑i.e., the magnetization relaxes slowly with increasing magnetic field before the avalanche condition is achieved͒.…”

Calculations of the onset temperature for tunneling in multispin systems

“…Quantum tunneling in spin systems has been the topic of many theoretical [3] and experimental studies [4][5][6][7] over the past few decades. At high enough temperature, quantum effects are not significant and transitions are due to thermal activation described by the Arrhenius law.…”

Phases of anisotropic dipolar antiferromagnets: Mean field theory and Monte Carlo simulations

“…Some of it comes from the availability of synthesized crystals of organometallic molecules 2 that behave at low temperature as single spins. [3][4][5][6] Owing to the large organic mass enveloping the magnetic cores of these molecules, dipole-dipole interactions are then dominant. 7 Long-range order has already been observed experimentally.…”