Detection of buried unexploded ordnance (UXO) is among the most urgent environmental needs for the Department of Defense. UXO of concern include items of widely varying size and depths (from the surface to many feet deep) with unknown orientations. Phenomenologically novel magnetic field sensors with better sensitivity and stability, lower cost, and small size could help support improved detection. The objective of this project was to fabricate a prototype device based on a single ferromagnetic nanocontact as the magnetic field sensor.

This research was based on experimental evidence of the ballistic magnetoresistance (BMR) phenomenon. The most receptive model of the BMR phenomenon is supported by spin dependent electron scattering from the magnetic domain wall (MDW) existing in the confined geometry of the nanocontact between two ferromagnetic electrodes with unusually high magnetoresistance.

This project demonstrated the functional magnetic field sensor devices based on nanocontact material with phase separated Ni and oxide/hydroxide domains (Fe(OH)₃). The observed values of ΔR/R are comparable if not better than state of the art giant magneto-resistance (GMR) magnetic field sensors. The simplicity and cost effectiveness of the fabrication concept used for the prototype devices have a promising application for the development of the future magnetic field sensors based on ferromagnetic nanocontacts.

The main result of this project is that the presence of electrochemically incorporated Fe(OH)₃ phase in Ni nanocontact matrix increases magnetoresistance values of the devices by factor of 10 to 50 as compared to the Ni single crystal nanocontact devices. This opens the frontier for future research on the materials that can be used for magnetic field sensors based on ferromagnetic nanocontacts. The relatively low values of R measured for the prototype devices with large ΔR/R indicate that electron conduction through the Ni phase is the main current path associated with measured resistance, however, positive and negative values of ΔR/R, as well as appearance of the hysterisis in magnetoresistance curves are indication that besides electron scattering from MDW some other more complex phenomena are contributing to the overall ΔR/R values.

The novel device and ferromagnetic nanocontact material as well as the facile device fabrication concept have demonstrated a cost effective route for development of sensing devices for the underground munitions detection applications. The new sensing concept could have the potential for improvement of detection systems.