TRANSPORT PHENOMENA OF SPIN-POLARIZED ELECTRON IN DOUBLE-TUNNELING BARRIER

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Exchange anisotropy has been investigated by torque magnetometory for MnPt (30 nm)/NiFe (5 nm) bilayers grown by the MBE method on MgO(001), SrTiO_3(001), and MgO(111) substrates. In-situ reflection high-energy electron diffraction observation and ex-situ X-ray diffraction measurements revealed that the MnPt layers have chemical order and have (100) uncompensated and (111) compensated plane parallel to the film plane, respectively for (001) and (111) substrate orientation. In PtMn/NiFe/SrTiO_3(001) unidirectional and uniaxial anisotropies have been observed, while in NiFe/PtMn/MgO(001) both the anisotropies almost disappeared and an anisotropy with four fold symmetry was observed. This anisotropy is thought to be closely related with the crystal anisotropy of PtMn.We have prepared NiFe/NiO bilayers and the NiFe/NiO/CoPt with various NiO thicknesses by RF magnetron sputtering under a dc magnetic field of 70 Oe, and investigated the magnetization process of these samples. In the NiFe/NiO bilayers, the exchange coupling field H_<ex> increased with increasing NiO thickness for t_<NiO>>10 nm, and becomes almost constant value of 110 Oe for t_<NiO>>20 nm. In the NiFe/NiO/CoPt trilayer, it is found that the magnetic moment of NiFe tend to align in the same direction as that of hard magnetic CoPt from the minor loop of the trilayer with NiO thickness of 10 nm. The loop shift depending on the direction of the CoPt moment did not appeared in the trilayer with the NiO thickness of 30 nm. The direction of the loop shift of NiFe layer was found to be controlled by changing of the direction of the applied field during the deposition.