Properties and measurement of scanning tunneling microscope fabricated ferromagnetic particle arrays (invited)

The low temperature magnetic properties of arrays of scanning tunneling microscope (STM) fabricated ferromagnetic particles have been studied as a function of their dimension using a novel high sensitivity Hall magnetometer. Iron deposits with controlled shape and nanometer scale diameters (∼25 nm) are formed using a STM to decompose a metalorganic precursor [Fe(CO) 5] in the active area of the measurement device. The hysteresis loops change significantly in going from nearly isotropic to oriented high aspect ratio (6:1 length to diameter) filamentary particles. In particles of intermediate aspect ratio and diameter the largest coercive field of 2.7 kOe is observed. This behavior as well as the characteristics of the Hall magnetometer (spin sensitivity of 10-14 emu/ Hz1/2) are described.