Spin Resolved Electronic Structures of Half-Metallic Ferromagnetic Single Crystalline Thin Films

本工作的目的是阐明分子束外延（MBE）方法生长的全Heusler型铁磁合金晶体薄膜的自旋极化能带结构，这些薄膜有望显示完全的自旋极化（半金属）电子态，利用自旋分辨光电子能谱（spin resolved photoelectron spectroscopy，SPAES）研究了面心立方结构的Co/Cu（001）超薄磁性薄膜并成功地获得了它的自旋相关电子结构。特别是首次观察到了负自旋极化的表面态。这一发现对理解隧道磁阻器件中磁输运现象的起源有重要作用。我们还对面心立方Fe超薄膜进行了类似的测量。用自旋极化光电子能谱测量了Fe 3d态的交换分裂，并给出了Fe 3d态交换分裂的正确值。本文研究了Heuler型铁磁合金NiMnSb，Ru_<2-x>Fe_xCrZ（Z=Si，Ge）和Co_2MnX（X=Si，Ga，Ge），其被预测为显示“半金属”电子结构，这些工作已在多个国际和国内会议上作了介绍。

The aim of this work is to clarify the spin polarized band structures of crystalline thin films of the full Heusler-type ferromagnetic alloys grown by molecular beam epitaxy (MBE) method, which are expected to show completely spin-polarized (half-metallic) electronic states, utilizing spin-resolved photoelectron spectroscopy.The ultra-thin magnetic film of fcc Co/Cu(001) has been fabricated and its spin dependent electronic structures have been successfully obtained. Especially, the negatively spin-polarized surface state has been firstly observed. This finding would play an important role to understand the origin of the magnetic transport phenomena in the tunneling magneto-resistance devices.We have done the similar measurement also for fcc Fe ultra-thin films. The observed spin-polarized photoelectron spectra have enabled us to estimate a correct value of the exchange splitting of Fe 3d states.The electronic structures in the bulk of the Heuler-type ferromagnetic alloys, NiMnSb, Ru_<2-x>Fe_xCrZ (Z=Si, Ge) and Co_2MnX (X=Si, Ga, Ge), which are predicted to show "half-metallic" electronic structures, have been clarified by the soft and hard X-ray photoelectron spectroscopies.The above-mentioned activities have been presented at several international and domestic conferences.