1. Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson Air Force Base, Ohio 45433, USA
2. Spintronics and Vaccum Nano-electronics Laboratory, Department of Electrical Engineering and Computer Science, University of Cincinnati, Cincinnati, Ohio 45221, USA
3. Air Force Research Laboratory, Sensors Directorate, Wright-Patterson Air Force Base, Ohio 45433, USA
4. Naval Research Laboratory, Washington, DC 20375, USA
5. Department of Mathematics, University of Surrey, Guildford, Surrey GU2 7XH, United Kingdom
6. Advanced Technology Institute and Department of Electrical and Electronic Engineering, University of Surrey, Guildford, Surrey GU2 7XH, United Kingdom