Observation of macroscopic spin phenomena in nanometer-scale magnets

A scanning tunneling microscope is used to locally deposit arrays of nanometer-scale magnets directly within the superconducting planar input coil of an integrated dc SQUID microsusceptometer. Low-temperature frequency-dependent magnetic-susceptibility measurements reveal a narrow resonance which grows and becomes independent of decreasing temperature. Studies as a function of magnet volume, spacing, and applied field are compared to recent predictions for magnetic macroscopic quantum tunneling in small particles. © 1990 The American Physical Society.