Invesigation on Mesoscopic Ferromagnetic Metals by Using Single Electron Transistor

In this project we have investigated the behavior of ferromagnetic single electron transistors(FSET‘s)in a magnetic field。With the term‘ferromagnetic single electron transistor’we mean a single electron transistor part of whose electrode is made of ferromagnetic metals，and in such a system we discovered a conductance oscillation almost periodic in applied magnetic field，which we call‘magneto-Coulomb oscillation(MCO)’。That was the start point of this project.In this project，we have especially clarified the mechanism of MCO from both experimental and theoretical point of view。We have also explored the possible application of this phenomenon as a tool to investigate the electronic structure of ferromagnetic metals and as a basis for functional operations of FSE devices.We have constructed a model to elucidate the phenomenon of MCO。In the model the origin of the magnetic-field induced conductance oscillation consists in the Zeemann effect and the spin polarization of the valence electrons in ferromagnetic metals.These two factors induce a change in chemical potential of the ferromagnetic metal in a magnetic field，just in a same way as by a gate potential in usual nonmagnetic SET‘s.We experimentally examined this model for Ni/Co/Ni，Co/Ni/Co，Al/Co/Al，Al/Al/Al，Al/Ni/Al and Ni/Al/Ni FSET’s，and have found semi-quantitative consistwith the model.By using this phenomenon conversely，we can determine a thermodynamic coefficient of a ferromagnetic metal(ζ/H)i D2N ier D2，whereζis the chemical potential，H means the magnetic field and N is the number of electrons in the ferromagnet.We have demonstrated this for Al/Co/Al，Al/Ni/Al and Ni/Al/Ni SET‘s.We have also indicated a possible operation of ferromagnetic single electron devices as magnetic-field driven functional devices utilizing MCO mechanism and magnetization reversal。

In this project we have investigated the behavior of ferromagnetic single electron transistors (FSET's) in a magnetic field. With the term 'ferromagnetic single electron transistor' we mean a single electron transistor part of whose electrode is made of ferromagnetic metals, and in such a system we discovered a conductance oscillation almost periodic in applied magnetic field, which we call 'magneto-Coulomb oscillation (MCO)'. That was the start point of this project. In this project, we have especially clarified the mechanism of MCO from both experimental and theoretical point of view. We have also explored the possible application of this phenomenon as a tool to investigate the electronic structure of ferromagnetic metals and as a basis for functional operations of FSE devices.We have constructed a model to elucidate the phenomenon of MCO. In the model the origin of the magnetic-field induced conductance oscillation consists in the Zeemann effect and the spin polarization of the valence electrons in ferromagnetic metals. These two factors induce a change in chemical potential of the ferromagnetic metal in a magnetic field, just in a same way as by a gate potential in usual nonmagnetic SET's. We experimentally examined this model for Ni/Co/Ni, Co/Ni/Co, Al/Co/Al, Al/Al/Al, Al/Ni/Al and Ni/Al/Ni FSET's, and have found semi-quantitative consistency with the model. By using this phenomenon conversely, we can determine a thermodynamic coefficient of a ferromagnetic metal (∂ζ/∂H)ィイD2NィエD2, where ζ is the chemical potential, H means the magnetic field and N is the number of electrons in the ferromagnet. We have demonstrated this for Al/Co/Al, Al/Ni/Al and Ni/Al/Ni SET's. We have also indicated a possible operation of ferromagnetic single electron devices as magnetic-field driven functional devices utilizing MCO mechanism and magnetization reversal.