Generation of very slow polarized positive muons

Morenzoni, E.; Kottmann, F.; Maden, D.; Matthias, Björn; Meyberg, M.; Prokscha, T.; Wutzke, Th.; Zimmermann, U.

doi:10.1103/physrevlett.72.2793

Cited by 167 publications

(120 citation statements)

References 14 publications

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“…energy spread) while conserving the initial full polarization 32 . The epithermal muons are extracted (by applying up to +20 kV to the moderator substrate), transported and focused by electrostatic elements to the sample.…”

Section: Methodsmentioning

confidence: 99%

Direct measurement of the electronic spin diffusion length in a fully functional organic spin valve by low-energy muon spin rotation

et al. 2008

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Electronic devices that use the spin degree of freedom hold unique prospects for future technology. The performance of these 'spintronic' devices relies heavily on the efficient transfer of spin polarization across different layers and interfaces. This complex transfer process depends on individual material properties and also, most importantly, on the structural and electronic properties of the interfaces between the different materials and defects that are common to real devices. Knowledge of these factors is especially important for the relatively new field of organic spintronics, where there is a severe lack of suitable experimental techniques that can yield depth-resolved information about the spin polarization of charge carriers within buried layers of real devices. Here, we present a new depth-resolved technique for measuring the spin polarization of current-injected electrons in an organic spin valve and find the temperature dependence of the measured spin diffusion length is correlated with the device magnetoresistance.R ecently great efforts have been undertaken to use the spin degree of freedom in electronic devices. These activities are fuelled by the potential prospects of spin-electronic (or 'spintronic') devices for example in terms of increased processing speed and integration, non-volatility, reduced power consumption, multifunctionality and their suitability for quantum computing 1 . The most common method for using the spin in devices is based on the alignment of the electron spin ('up' or 'down') relative to either a reference magnetic field or the magnetization orientation of a ferromagnetic layer. Device operation normally proceeds with measuring a quantity such as the electrical current that depends on how the degree of spin alignment is transferred across the device. The so-called 'spin valve' is a prominent example of such a spin-enabled device that has already revolutionized hard-drive read heads and magnetic memory 1 . The efficient transfer of spin polarization in real device structures remains one of the most difficult challenges in spintronics, because it is dependent on more than just the properties of the individual materials that comprise the device.Recently 2,3 , the use of organic materials in spintronics has become of significant interest, primarily owing to their ease and small cost of processing and electronic and structural flexibility. Furthermore, the extremely long spin coherence times found in organic materials offer considerable advantages over other materials 3 . This favourable property is related to two factors, first the weak spin-orbit coupling of light elements such as carbon and second to the small nuclear hyperfine interaction 4,5 . The latter arises because the electron transport in π-conjugated molecules is normally confined to molecular states, delocalized to the carbon rings, the predominant isotope of which, 12 C, has zero nuclear spin 4 .A common way to measure spin diffusion is based on time-resolved optical techniques, where spin-polarized charge carrie...

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Section: Methodsmentioning

confidence: 99%

Direct measurement of the electronic spin diffusion length in a fully functional organic spin valve by low-energy muon spin rotation

et al. 2008

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“…Unlike conventional µSR techniques which make use of the energetic muons (∼ 4 MeV) originating from π + decay at rest ("surface" muons), LE-µSR makes use of epithermal muons (∼ 15 eV) extracted after moderation of surface muons from a thin film of a weakly bound van der Waals cryosolid (wide band gap insulator) 21,22 . By re-accelerating the epithermal muons up to 20 keV and biasing the sample, it is possible to tune the implantation energy in the range of 0.5 to 30 keV and thus to implant the muons beneath the surface of any material in a range of up to about 300 nm and a spatial resolution down to 1 nm.…”

Section: Methodsmentioning

confidence: 99%

Observation of nonexponential magnetic penetration profiles in the Meissner state: A manifestation of nonlocal effects in superconductors

et al. 2005

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Implanting fully polarized low energy muons on the nanometer scale beneath the surface of a superconductor in the Meissner state enabled us to probe the evanescent magnetic field profile B(z) (0 < z 200nm measured from the surface). All the investigated samples [Nb: κ ≃ 0.7(2), Pb:κ ≃ 0.6(1), Ta: κ ≃ 0.5(2)] show clear deviations from the simple exponential B(z) expected in the London limit, thus revealing the non-local response of these superconductors. From a quantitative analysis within the Pippard and BCS models the London penetration depth λL is extracted. In the case of Pb also the clean limit coherence length ξ0 is obtained. Furthermore we find that the temperature dependence of the magnetic penetration depth follows closely the two-fluid expectation 1/λ 2 ∝ 1 − (T /Tc) 4 . While B(z) for Nb and Pb are rather well described within the Pippard and BCS models, for Ta this is only true to a lesser degree. We attribute this discrepancy to the fact that the superfluid density is decreased by approaching the surface on a length scale ξ0. This effect, which is not taken self-consistently into account in the mentioned models, should be more pronounced in the lowest κ regime consistently with our findings.

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“…A low-energy µ + beam with tunable energy in the keV regime [2] plays an important role in the µSR field because these muons can be used to investigate thin films. The Low Energy Muon (LEM) beam line at PSI shown in figure 1 is delivering µ + with tunable kinetic energy between 0.5 and 30 keV allowing the study of thin films and multilayers as a function of the implantation depth ranging from 0.5 nm to a few hundred nm [3,4].…”

Section: Introductionmentioning

confidence: 99%

Geant4 simulation of the PSI LEM beam line: energy loss and muonium formation in thin foils and the impact of unmoderated muons on the μSR spectrometer

et al. 2015

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The PSI low-energy µSR spectrometer is an instrument dedicated to muon spin rotation and relaxation measurements. Knowledge of the muon beam parameters such as spatial, kinetic energy and arrival-time distributions at the sample position are important ingredients to analyze the µSR spectra. We present here the measured energy losses in the thin carbon foil of the muon start detector deduced from time-of-flight measurements. Muonium formation in the thin carbon foil (10 nm thickness) of the muon start detector also affect the measurable decay asymmetry and therefore need to be accounted for. Muonium formation and energy losses in the start detector, whose relevance increase with decreasing muon implantation energy (< 10 keV), have been implemented in Geant4 Monte Carlo simulation to reproduce the measured time-of-flight spectra. Simulated and measured time-of-flight and beam spot agrees only if a small fraction of so called "unmoderated" muons which contaminate the mono-energetic muon beam of the µSR spectrometer is introduced. Moreover the sensitivity of the beam size and related upstream-downstream asymmetry for a specially shaped "nose" sample plate has been studied for various beam line settings, which is of relevance for the study of thermal muonium emission into vacuum from mesoporous silica at cryogenic temperatures.

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Generation of very slow polarized positive muons

Cited by 167 publications

References 14 publications

Direct measurement of the electronic spin diffusion length in a fully functional organic spin valve by low-energy muon spin rotation

Direct measurement of the electronic spin diffusion length in a fully functional organic spin valve by low-energy muon spin rotation

Observation of nonexponential magnetic penetration profiles in the Meissner state: A manifestation of nonlocal effects in superconductors

Geant4 simulation of the PSI LEM beam line: energy loss and muonium formation in thin foils and the impact of unmoderated muons on the μSR spectrometer

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