Microscopic Study on the Surface Magnetism by Ultra-slow Muon

1989年初，日本政府批准了日本东京大学介子科学实验室的一项新的超慢μ介子通道的建设计划。本研究项目的研究员长峰说。新通道可望在1991年产生高强度超慢束流，其强度比常规装置高几个数量级，将成为研究表面磁性的有力工具。考虑到研究项目的未来可能性，我们改变了最后一年的研究计划，集中精力发展高强度光束，而不是使用低强度光束完成研究。高强度超慢μ子束的研制（i）基于热μ子的激光激发方法，确定了超慢μ子新通道的概念和基本设计。（ii）观察到Si（100）晶片上SiO_2薄层向真空中的热μ ~（？）发射。SiO_2厚度对产额的影响在3 nm处达到最大值，这对研究热μ子发射机制具有重要意义。2.μ子自旋弛豫研究多层结构磁性单层膜的磁性（i）在石墨的巨大背景下检测到2%的吸附在石墨表面的氧单层膜的uSR信号，为12 K下二维反铁磁体的磁相变提供了证据。(ii)在人造金属超晶格MnSb上，通过初步的实验，仔细地估计了信号/背景比大于20%。结果鼓励对该主题进行详细的实验。

In the beginning of 1989, the government approved a plan to construct a new ultra-slow muon channel in Meson Science Laboratory, University of Tokyo proposed by K. Nagamine, a investigator of the present research project. The new channel is expected to produce high-intensity ultra-slow beam in 1991 with several orders of the magnitude higher than that produced by the conventional facility and will be powerful tool to study the surface magnetism. Considering the future possibilities of the research project, we changed the re- search plan of the final year to concentrate on the development of the high-intensity beam instead to complete the study by using the low intensity beam.The primary results of the research project are summarized as follows; 1. Development of the High-intensity Ultra-slow Muon Beam (i) The concept and the basic design of the new channel of ultra- slow muon is decided based on the laser-excitation method of the thermal muonium. (ii)Thermal muonium emission from thin SiO_2 layer on a Si(100) wafer into vacuum is observed. The SiO_2 thickness dependence of the yield, which becomes maximum at 3 nm, gives the important in formation about the mechanism of the thermal muonium emission. 2. Magnetism of the Magnetic Monolayers with Multilayered Structure by Muon Spin Relaxation (i) The uSR signal of 2% of Oxygen monolayers adsorbed on Graphite is detected from a huge background of Graphite and it gives the evidence for the magnetic phase transition of 2-D antiferromagnet at 12K. (ii) On artificial metallic superlattice MnSb, the signal/background ratio has been carefully estimated to be more than 20% by the preliminary experiment. The result encourages to perform detail experiments on the subject.