2006 Fiscal Year Final Research Report Summary
Application of ultra slow muon beam for the surface and thin film
| Project/Area Number |
16206005
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| Research Category |
Grant-in-Aid for Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Thin film/Surface and interfacial physical properties
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| Research Institution | High Energy Accelerator Research Organization |
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Principal Investigator |
MIYAKE Yasuyuki High Energy Accelerator Research Organization, Institute of Materials Structure Science, Professor (80209882)
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| Co-Investigator(Kenkyū-buntansha) |
MATSUDA Yasuyuki RIKEN, Advanced Meson Science Laboratory, Senior Research Scientist (70321817)
PAVEL Bakule 高エネルギー加速器研究機構, 理化学研究所・岩崎先端中間子科学研究室, 協力研究員
IKEDO Yutaka Toyota Central R&D Labs., Inc., Research Scientist
SHIMOMURA Koichiro High Energy Accelerator Research Organization(KEK), Institute of Materials Structure Science, Associate Lecturer (60242103)
NISHIYAMA Kusuo High Energy Accelerator Research Organization(KEK), Institute of Materials Structure Science, Professor (50164611)
ARAKI Wakako RIKEN, Advanced Meson Science Laboratory, Contract Researcher
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| Project Period (FY) |
2004 – 2006
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| Keywords | muon / ultra slow muon / Thin Film / Lyman-alpha / μ^+SR / Resonant ionization Method / Perovskyte / accelerator |
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| Research Abstract |
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
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Research Products
(28 results)
