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

用扭矩磁强计研究了用分子束外延方法在MgO(001)、SrTiO3(001)和MgO(111)衬底上生长的MnPt(30 Nm)/NiFe(5 Nm)双层膜的交换各向异性。原位反射高能电子衍射仪和X射线衍射仪的测量结果表明，在(001)和(111)两种衬底取向上，MnPt层具有化学有序性，并具有平行于薄膜平面的(100)无补偿面和(111)补偿面。在PtMn/NiFe/SrTiO_3(001)中观察到了单向和单轴各向异性，而在NiFe/PtMn/MgO(001)中，这两种各向异性几乎都消失了，并且观察到了具有四重对称性的各向异性。这种各向异性被认为与PtMn的晶体各向异性密切相关。我们在70 Oe的直流磁场下用射频磁控溅射方法制备了不同NiO厚度的NiFe/NiO双层膜和NiFe/NiO/CoPT薄膜，并研究了这些样品的磁化过程。在NiFe/NiO双层膜中，当NiO厚度为10 nm时，交换耦合场H_&lt；ex&gt；随NiO厚度的增加而增大，而对于t_&lt；NiO&gt；&gt；20 nm，交换耦合场H_&lt；ex&gt；几乎不变，为110Oe。在NiFe/NiO/CoPT三层膜中，从NiO厚度为10 nm的三层膜的小环开始，NiFe的磁矩倾向于与硬磁CoPT的磁矩方向一致。在NiO厚度为30 nm的三层膜中，没有出现依赖于Copt矩方向的环移。结果表明，在沉积过程中，改变外加电场的方向可以控制NiFe层的环移方向。

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.