peb@uunet.uu.net (Paul Baclaski) (04/20/91)
This is from ba.seminars, an IBM ARC (Almaden Research Center) announcement. 04/26 - QUANTUM TUNNELING AND SPIN DYNAMICS IN NANOMETER-SCALE MAGNETS D. D. Awschalom, IBM Watson Research Center, Yorktown Heights, NY Phys. Sci. Colloq. Fri., April 26 9:30 a.m. Room: Aud. A * * * SPECIAL MINISYMPOSIUM ON THIN FILM MAGNETISM * * * Recently, small ferromagnetic particles have been proposed as a system where quantum mechanics is likely to produce measurable manifestations on the macroscopic level, such as macroscopic quantum tunneling (MQT). It is predicted that the magnetization of such single domain systems can tunnel between local energy minima separated by an energy barrier determined by the magnetic anisotropy, and may be observable at low temperature. These experiments use two distinct superconducting integrated circuits to form a very sensitive, miniature dc SQUID-based susceptometer. Magnets with nanometer-scale dimensions (15 nm) are fabricated using a modified scanning tunneling microscope to locally deposit iron molecules directly into one of a pair of microscopic gradiometer pickup loops. Low-temperature (approx 20 mK) frequency-dependent magnetic susceptibility measurements reveal a narrow resonance which grows and becomes temperature-independent below 100 mK. Although qualitatively suggestive of MQT, studies as a function of magnet volume, spacing, and applied field reveal new low-temperature spin dynamics in small magnetic systems which cannot be reconciled with recent theoretical predictions for magnetic MQT. Host: S. Parkin