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

用转矩磁测量法研究了分子束外延（MBE）法在MgO（001）、SrTiO_3（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观察和非原位X射线衍射测量表明，MnPt层具有化学有序性，在（001）和（111）衬底取向上分别具有平行于膜面的（100）未补偿面和（111）补偿面。在PtMn/NiFe/SrTiO_3（001）中观察到单向和单轴各向异性，而在NiFe/PtMn/MgO（001）中，各向异性几乎消失，观察到四重对称的各向异性。我们在70 Oe的直流磁场下用射频磁控溅射法制备了NiFe/NiO双层膜和不同NiO厚度的NiFe/NiO/CoPt，并研究了这些样品的磁化过程。在NiFe/NiO双层膜中，当t&gt;10 nm时，交换耦合场H<ex>随NiO厚度的增加而增大<NiO>，当t&gt;20 nm时，H几乎保持在110 Oe<NiO>。在NiFe/NiO/CoPt三层膜中，当NiO厚度为10 nm时，从三层膜的次环上看，NiFe的磁矩趋向于与硬磁CoPt的磁矩相同的方向。在NiO厚度为30 nm的三层膜中没有出现依赖于CoPt磁矩方向的环位移。发现NiFe层的回线位移的方向可以通过改变沉积过程中外加电场的方向来控制。

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.