ELASTIC AND INELASTIC ELECTRON TUNNELING IN MAGNETIC METAL/MAGNETIC LAYERED SEMICONDUCTOR HETEROJUNCTIONS

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We have studied elastic and inelastic electron tunneling (IET) in metal/insulator/metal (MIM) junctions having ferromagnetic metal electrodes and/or antiferromagnetic insulating layrs. The insulating layrs are single crystal thin films cleaved from the single crystals of layred semiconductors, transition metal chalcogeno-phosphates for antiferromagnetic layrs and III-VI compounds for nonmagnetic layrs. Several MIM junctions with an MnPS_3 antiferromagnetic insulating layr sandwiched between two ferromagnetic Fe electrodes show tunnel current in current-voltage characteristics, although the junctions have effectively the metallic current paths parallel and/or series to tunnel current paths in the junctions. Moreover, some additional informations about tunneling phenomena in MIM junctions were also obtained :(a) The tunneling characteristics in Pb/MnPSe_3/Pb junctions show the interactions between tunneling electrons and MnPSe_3 antiferromagnetic magnons as well as MnPSe_3 phonons.(b) Both tunneling spectra for Sb/GaS/Sb and Sb/GaS/Pb junctions reflect band structures in semimetallic Sb. The IET processes due to Sb phonons as well as GaS ones in the symmetrical Sb/GaS/Sb junctions are reduced due to small Fermi surfaces of Sb compared with those in the asymmetrical Sb/GaS/Pb junctions.(c) Self energy effects of Al are observed for the first time in the tunneling characteristics in Al/GaS/Pb junctions. Furthermore, self enrgy effects of Ag and Cu are inferred from the tunneling spectra for Ag/GaS/Pb and Cu/GaS/Pb junctions.(d) The optical absorption spectra of In_<2/3>PS_3 single crystals show an indirect absorption edge. The energy values of the exciton gap and those of the momentum conserving phonons in In_<2/3>PS_3 are reduced from the spectra.