Mustafa Bal, Dartmouth
Abstract
Single-molecule magnets (SMMs), a class of molecular nanomagnets, received much attention in recent years as they display unique classical and quantum properties. SMMs, similar to classical magnets, are bistable and exhibit hysteresis below a blocking temperature of typically a few Kelvins. Owing to their small number of spin states, SMMs have discrete energy levels and display fascinating quantum effects, such as quantum tunneling of magnetization and interference between tunneling paths.
Most of our studies are concentrated on the molecular nanomagnet Fe8 with a spin ground state S=10. A giant-spin Hamiltonian, giving rise to a double-well potential, describes the spin dynamics at low temperature remarkably well. Experimental results will be reported on magnetization relaxation in a single crystal of the Fe8 SMM induced by a single pulse of resonant millimeter-wave radiation. The spin dynamics at sub-microsecond time scales are explored by employing an inductive pick-up loop coupled to a SQUID voltmeter. This set-up allowed the measurement of the rate of magnetization change (dM/dt) as a function of time at time scales as short as tens of nanoseconds. The onset of the radiation pulse causes the sample magnetization to relax with a few-microsecond relaxation time followed by a remarkably fast heating of the sample. The results of a systematic study of this short-time scale magnetization behavior and its dependence on experimental parameters, as well as the real-time observation of quantum tunneling of magnetization will be presented.