Fabrication of Tunneling Magnetoresistance Devices using Novel Room-temperature Ferromagnetic Semiconductor MnGeP_2

本文介绍了在日本科学促进会2005-2006财年(B)(2)类科学研究资助项目17360009的资助下，利用新型室温铁磁半导体MnGeP2制作隧道磁阻器件的研究成果。该项目的目的是阐明在2001-2003财政年度MEXT-JSPS科学研究资助项目下进行的黄铜矿型室温铁磁半导体的最佳制备条件，为了实现隧道磁阻器件，制备平坦度较高的磁性薄膜是必不可少的。然而，在GaAs和InP衬底上制备的MnGeP2薄膜表面粗糙，表面形貌差，不适合用于TMR器件。为了改善表面平整度，我们引入了GE Bu…更多的FER层，这被证明是有效的。然而，通过透射电子显微镜和能谱分析发现，MnGeP2织构中混入了MnNP颗粒。为了抑制相分离，我们根据第一性原理热力学计算提高了衬底温度。然而，所得到的薄膜在室温下没有自发磁化，尽管薄膜处于单相状态。因此，我们改变了策略，开始探索获得平坦度足够高的MnP薄膜的最佳条件，因为MnP的磁性已经广为人知。此外，在提高衬底温度下制备高质量的MnGeP2薄膜的过程中，通过仔细的扫描电子显微镜观察，我们发现衬底表面有纳米晶须自组装生长。通过电子显微镜观察和成分分析，发现晶须既有Ge基晶须，也有MnP基晶须。由于以往的报道大多使用Au作为催化剂，因此纳米晶须的无催化剂生长引起了人们的兴趣。因此，这些结果被包括在本报告中，尽管这一发现不是本研究计划的主要主题。较少

This report describes achievements of the research project "Fabrication of Tunneling Magneto-resistance Devices using Novel Room-temperature Ferromagnetic Semiconductor MnGeP2" conducted under the support of the Grant-in-Aid for Scientific Research from Japan Society for Promotion of Science for 2005-2006 FY, Category (B) (2), No.17360009.The purpose of this project is to elucidate the optimum fabrication condition of MnGeP2 films which was discovered during the research for chalcopyrite-type room-temperature ferromagnetic semiconductors conducted under the 2001-2003 FY Grant-in-Aid for Scientific Research of MEXT-JSPS, and fabricate tunneling magneto-resistance (TMR) devices using these films.For realization of TMR devices it is essential to prepare magnetic films with improved flatness. However, MnGeP2 films prepared on GaAs and InP substrates suffer poor surface morphology with roughness and were found to be unsuitable for tMR devices. To improve surface flatness we introduced Ge bu … More ffer layer, which proved to be effective. However, it is found by TEM and EDX observation that MnP grains are mixed among MnGeP2 texture.In order to suppress phase separation we raised the substrate temperature following the first principle thermodynamic calculation. The resulting films, however, showed no spontaneous magnetization at room temperature, despite that the films are in single phase state. We therefore changed the strategy and started to exploit optimum conditions to obtain MnP thin films with sufficient flatness, since the magnetic properties of MnP has been well known.Using MnP and CoFe as electrodes we prepared magnetic tunnel junctions which showed magneto-resistance effect. Thus we have established a technique to obtain MTJ consisting of MnGeP2.In addition, during preparation of high quality MnGeP2 films at elevated substrate temperatures we have found self-assembled growth of nanometer-sized whiskers on the surface of the substrates by careful SEM observations. By TEM observations and compositional analyses whiskers are found to be either Ge-based or MnP based crystals. Catalyst-free growth of nano-whiskers is of interest since most of previous report used Au as catalyst. Therefore the results are included in this report although this finding is not a main subject of this research program. Less