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

本报告介绍了在日本科学振兴会2005-2006年度科学研究补助金（B类）（2）的支持下开展的研究项目“使用新型室温铁磁半导体MnGeP 2制造超导磁阻器件”的成果，本项目的目的是阐明在2001-2003财政年度资助的黄铜矿型室温铁磁半导体研究中发现的MnGeP 2薄膜的最佳制备条件。为MEXT-JSPS的科学研究提供了帮助，并利用这些薄膜制作了隧道磁阻（TMR）器件。然而，在GaAs和InP衬底上制备的MnGeP 2膜具有粗糙的表面形貌，并且被发现不适合用于tMR器件。为了提高表面平整度，我们引入了Ge Bu 关于我们 层，这被证明是有效的。TEM和EDX观察发现，MnGeP 2织构中夹杂着MnP晶粒，为了抑制相分离，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，在室温下没有显示出自发磁化，尽管该薄膜是在单相状态。由于MnP的磁性是众所周知的，因此我们改变了策略，开始探索最佳条件以获得足够平整的MnP薄膜。以MnP和CoFe为电极，我们制备了具有磁阻效应的磁性隧道结。此外，在高温下制备高质量MnGeP_2薄膜的过程中，通过SEM观察，我们发现在衬底表面自组装生长了纳米尺寸的晶须。通过TEM观察和成分分析，发现晶须是Ge基或MnP基晶体。无催化剂生长纳米晶须是感兴趣的，因为大多数以前的报告使用Au作为催化剂。因此，尽管这一发现不是本研究项目的主要主题，但本报告仍包含了结果。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