Application of ultra slow muon beam for the surface and thin film

超慢μ子​​束在表面和薄膜中的应用

• 批准号: 16206005
• 负责人: MIYAKE Yasuyuki
• 金额: $ 29.29万
• 依托单位: High Energy Accelerator Research Organization
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (A)
• 财政年份: 2004
• 资助国家: 日本
• 起止时间: 2004 至 2006
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-16206005/
• 关键词: muon; ultra slow muon; Thin Film; Lyman-alpha; μ^+SR; Resonant ionization Method; Perovskyte; accelerator; 偏極; スピン; 低速ミュオン; 物性; 水素原子; 表面; レーザー

Spin polarised positive muons (1+) have a unique application in condensed matter physics as extremely sensitive magnetic micro-probes. Muons implanted into a host material can convey information about the local magnetic field distribution and fluctuations through rotation or relaxation of its spin. The change of muon spin distribution can be observed by measuring angular distribution of positrons which muons decay to. This technique is called 1SR, and have been used for various materials. Until now, 1SR experiments have been carried out by using surface muons, whose range is approximately 1.4mm in water and 0.3mm in iron respectively. In order to study magnetic properties of thin films or multi-layered structure with the depth sensitivity on nano-meter scale, muon beams whose kinetic energy can be varied from sub-keV to a few tens keV, with its uncertainty within several per cent, are required. We have been developing a technique1), which allows us to produce muons with kinetic energy … More as low as 0.2eV by resonant laser ionization of thermal muonium atoms (1+e_i). Since our first generation of lowenergy muons in 2001_2), we have increased the power of ionizing lasers, optimised both the focusing of the incident muon beam and the transport efficiency of low-energy muons after re-acceleration. This has resulted the yield of low-energy muons being increased by a few hundreds fold to 15 1+/sec at the sample position. Our measurement shows no saturation of the yield with the power of ionizing laser, suggesting further increase can be expected as laser system being improved. The characteristics of the low-energy muons were measured by a 2-dimensional position sensitive MCP. Observed beam profile at the sample position showed the muons were tightly focused to a spot of 3x4mm2 (FWHM), which is more than 100 times smaller than the size of conventional surface muon beam. The temporal width of the low-energy muon was less than lOnsec, which is 10 times narrower than that of surface muon beam. These results demonstrate that our method is ideally suited to pulsed muon sources, including the RIKEN-RAL muon facility. A compact 1SR spectrometer has been installed in the beam line. A solenoid-type magnet can apply a magnetic field of up to 700 Gauss at the sample position. Plastic scintillators cover around 80% of total solid angle from the sample position, maximising the positron signal from low-energy muons. A GM refrigerator is mounted to the spectrometer, enabling to cool a sample down to 10K. As a demonstration of the high time resolution of the low-energy muon beam, We have implanted 15keV muons into Si0_2 and observed the spin precession signal from triplet muonium in transverse magnetic field of 50 Gauss and 100 Gauss at room temperature. There was no observed reduction of asymmetry between two measurements, which implies that higher frequencies of up to 30MHz could be observed without a loss of asymmetry. As the first 1SR experiment using low-energy muon beam, we are considering to measure magnetic properties of a thin perovskite manganite film grown on SrTiO_3 substrates. Perovskite show varieties of interesting phenomena, like colossal magnetoresistance (CMR) effect, which have large potencial for device application. It is understood, though, that thephase diagram of thin perovskite manganite films are different from that of bulk crystals due to lattice strainform the substrates. The measurement of such will be a good demonstration of capability of loweenergy muons as a unique probe of magnetic properties for thin films and multi-layer system. Less

自旋极化的正μ子（1+）在凝聚态物理学中作为极灵敏的磁性微探针有着独特的应用。注入到主体材料中的μ子可以通过其自旋的旋转或弛豫来传达关于局部磁场分布和波动的信息。通过测量μ子衰变到正电子的角分布，可以观察到μ子自旋分布的变化。这种技术被称为1 SR，并已用于各种材料。到目前为止，人们已经用表面μ子进行了1 SR实验，其射程在水中约为1.4mm，在铁中约为0.3mm。为了研究具有纳米级深度灵敏度的薄膜或多层结构的磁性，需要μ子束的动能范围从亚keV到几十keV，其不确定度在百分之几以内。我们一直在开发一种技术，它可以让我们产生具有动能的μ子 ...更多信息 用共振激光电离热μ原子（1+e_i），其能量可低至0.2eV。自2001_2）第一代低能μ子以来，我们提高了电离激光器的功率，优化了入射μ子束的聚焦和重新加速后低能μ子的传输效率。这导致低能μ子的产率在样品位置处增加数百倍至15 1+/sec。我们的测量结果表明，产额与电离激光功率没有饱和，这表明可以预期进一步提高激光系统的改进。用二维位置敏感微通道板测量了低能μ子的特性。在样品位置处观察到的束轮廓显示，μ子被紧紧地聚焦到3x 4 mm 2（FWHM）的光斑，这比常规表面μ子束的尺寸小100倍以上。低能μ子束的时间宽度小于10纳秒，比表面μ子束的时间宽度窄10倍。这些结果表明，我们的方法非常适合脉冲μ子源，包括RIKEN-RAL μ子设施。一个紧凑的1 SR光谱仪已安装在光束线。螺线管型磁铁可以在样品位置施加高达700高斯的磁场。塑料反射器覆盖了样品位置约80%的总立体角，最大限度地提高了来自低能μ子的正电子信号。GM制冷机安装在光谱仪上，能够将样品冷却到10 K。作为低能μ子束高时间分辨率的证明，我们在室温下将15 keV μ子注入SiO_2中，在50高斯和100高斯的横向磁场中观察到了三重态μ子的自旋进动信号。在两次测量之间没有观察到不对称性的降低，这意味着可以观察到高达30 MHz的更高频率而不损失不对称性。作为第一个利用低能μ子束的1 SR实验，我们正在考虑测量在SrTiO_3衬底上生长的钙钛矿锰氧化物薄膜的磁性。超导材料中存在着各种有趣的现象，如巨磁电阻效应，这些现象在器件应用中具有很大的潜力。然而，可以理解的是，由于衬底的晶格应变，钙钛矿锰氧化物薄膜的相图不同于大块晶体的相图。这种测量将很好地证明低能μ子作为薄膜和多层系统磁性的独特探针的能力。少

项目成果

Pulsed source of ulatra low-energy muons at RIKEN-RAL

RIKEN-RAL 的超低能 μ 子脉冲源

• 发表时间: 2006
• 期刊: Physica B 374-375
• 作者: P.Bakule;Y.Matsuda;M.Iwasaki;Y.Miyake;K.Nagamine;Y.Ikedo;K.Shimomura;P.Strasser
• 通讯作者: P.Strasser

Development of low-energy muon beam line at the RIKEN-RAL muon facility

RIKEN-RAL μ子设施开发低能μ子束线

• 发表时间: 2006
• 期刊: RIKEN Accel. Prog. Rep. 39
• 作者: Y. Matsuda;et. al.
• 通讯作者: et. al.

Prospects for U1tra Low Energy Muon Beam at J-PARC

J-PARC 对 U1tra 低能 μ 子束的展望

• 发表时间: 2008
• 期刊: IPS08 Abstract
• 作者: P. Bakule;et. al.
• 通讯作者: et. al.

Development of low-energy beam line at the RIKEN-RAL muon facility

RIKEN-RAL muon 设施低能束线的开发

• 发表时间: 2006
• 期刊: RIKEN Accel. Prog. Rep.
• 作者: Y.Matsuda;P.Bakule;Y.Ikedo;K.Ishida;M.Iwasaki;S.Makimura;T.Matsuzaki;Y.Miyake;K.Nagamine;K.Shimomura;P.Strasser
• 通讯作者: P.Strasser

Pulsed source of ultra low energy positive muons for near-surfaceμSR studies

用于近地表μSR研究的超低能量正μ子脉冲源

• 发表时间: 2008
• 期刊: Nucl. Instr. and Meth. in Phys. Res. B 266
• 作者: P. Bakule;Y. Matsuda;Y. Miyake;K. Nagamine;M. Iwasaki;Y. Ikedo;K. Shimomura;P. Strasser;S. Makimura
• 通讯作者: S. Makimura