No abstract

Quantum tunneling, the passage of a microscopic system from one state to another by way of a classically forbidden path, is theoretically possible in the macroscopic world. One can now make direct observations of such macroscopic quantum tunneling in very small magnetic structures. This is possible because of significant advances both in the ability to obtain magnetic systems of almost any desirable size, shape, and composition and in the development of superconducting instrumentation for the detection of extremely weak magnetic signals. As an example, measurements on magnetic horse spleen ferritin proteins with the predictions of quantum tunneling theory are discussed and shown.

The application of picosecond magneto-optic sampling techniques to studies of the magnetization dynamics of thin-film recording heads is described. Time-resolved magnetization measurements are performed using picosecond stroboscopic scanning Kerr microscopy. A Faraday probe is used to monitor the coil excitation current with the same optical setup, yielding a direct measure of the magnetic propagation delay through the head. This delay is found to have a marked spatial dependence across the face of the pole tips. As an aid to visualization of the spatial dependence, scanned images of the polar Kerr rotation at fixed time delays are acquired.

Spin-dependent dynamics of polarized carriers in a series of Znjx Mn x Se/ZnSe superlattice structures are directly observed by time-resolved upconversion photoluminescence spectroscopy at low temperatures. Polarization measurements in small magnetic fields reveal spin-flip scattering of carriers confined within a magnetic quantum well. A marked change in the dynamics is observed with increasing field and subsequent spin superlattice formation. Exciton lifetimes and spin relaxation are seen to be strongly dependent on both the energy and location of spin states in the heterostructure.