The rutile crystal structure contains vacant channels along the tetragonal $c$-axis that provide both sites and a diffusion path for small interstitial impurities. Here, we present beta-detected nuclear magnetic resonance ($\beta$-NMR) measurements of the quadrupole splitting of implanted $^8$Li$^+$ in two isostructural rutile single crystals: TiO$_2$ and MgF$_2$. We compare our results with...
Even though there are several muon spin rotation and relaxation ($\mu$SR) studies in water/ice [1-6], recently, we report the oscillation in the zero-field spectra of muons in ice which is attributed to the spin–dipole interactions between the muon in MuOH and neighboring protons and to hyperfine transitions of triplet states of axially symmetric anisotropic muonium in ice [7]. The Mu-H...
The organic charge transfer salt TTF-CA contains 1D chains with alternating molecules of the electron donor TTF and the electron acceptor chloranil (CA). At high temperatures the molecules are in a charge neutral state (N), but below 80 K there is an ionic state (I) with a partial charge transfer from TTF to CA. Various topological excitations are possible in this system [1], e.g. domain walls...
A novel formulation of the strong-collision (SC) model is presented in terms of a "SC" projection operator. This very compact and concise notation is ideally suited for the systematic development of the dynamic time evolution of each isochromat in the static frequency spectrum via, for example, cumulant expansion. The resulting model is compared with a non-trivial case for which the strong...
Muon spin rotation and relaxation spectroscopy is a well established experimental probe used to investigate the properties of a wide range of condensed matter systems. However, beyond the properties revealed directly by the best fit parameters of the experiment, computational methods can effectively quantify the microscopic interactions underlying the experimentally observed signal, thus...
The quantum behavior of light nuclei and other particles in materials challenges classical intuition and introduces novel phenomena. Here we demonstrate that muon spin spectroscopy (μSR) is a powerful tool for exploring the quantum effects of light particles, such as the muon, in condensed matter. The muon’s quantum nature is profoundly influenced by the surrounding, offering a unique probe...
The muon spin rotation ($\mu\text{SR}$) technique has been applied to determine the behavior of the in-plane magnetic penetration depth ($\lambda_{ab}$) in the vortex state of the unconventional superconductor Sr$_2$RuO$_4$ as a means of gaining insight into its still unknown superconducting order parameter. A recent $\mu\text{SR}$ study of Sr$_2$RuO$_4$ reported a $T$-linear temperature...
In order to broaden the applications of muon across various research fields, develop the spectrometers and experimental areas dedicated to particular fields, we develop different secondary beamlines (experimental areas) at Muon Science Establishment (MUSE), Japan Proton Accelerator Research Complex (J-PARC) [1-6]. For the study of the functional properties of materials using surface muons, we...
In cubic chiral magnets, Dzyaloshinskii-Moriya (DM) interactions within the chiral crystal structure result in diverse magnetic textures, including skyrmion lattices (SkL) and chiral soliton lattices, which hold promise for spintronic and magnonic devices. Among these, MnSi has been extensively studied due to the SkL formation in the so-called “A-phase” just below Tc.
Recently, it was...
The Phase II upgrade project of the China Spallation Neutron Source (CSNS) includes the construction of a surface muon beam line and a muon spin rotation/relaxation/resonance (μSR) spectrometer, which will be the first μSR spectrometer built in China. Here, we report the conceptual design of the spectrometer, including the detector arrangement, magnets, sample environment (SE) and sample...
$\mu$SR is a spectroscopy using a spin-polarized muon beam. It is a method to observe the muon spin rotation, relaxation and resonance by using the detection of positrons emitted asymmetrically to the muon spin axis, and is widely used as one of the physical property methods to search for magnetic fields inside materials. However, the conventional $\mu$SR can only measure physical properties...
$\mu$SR is a powerful technique for probing internal magnetic fields and their dynamic behavior and it has been widely used in the study of magnetic and superconducting materials. However, due to limitations such as the relatively small sample volume, there are very few experimental reports of $\mu$SR under high-pressure conditions exceeding 10 GPa.
To address this challenge, we are...
The dynamics of polymer glasses have been shown to be enhanced within a few nanometers of an interface. This enhanced surface mobility has technological implications for processing and applications of glasses. An open question is how the chemical structure of a polymer affects the dynamics in the near surface region, but this is extremely challenging to study. Previous studies using bulky...
While ruthenium oxide RuO$_2$ with a rutile structure has long been regarded as a Pauli paramagnetic metal, it has recently attracted much attention as a candidate for the “altermagnet". The existence of an antiferromagnetic (AFM) order, essential for the altermagnet, has been claimed by recent neutron diffraction study [1]. However, the reported Ru magnetic moment size $|m_\mathrm{Ru}|$ =...
The science program of elemental analysis is a rapidly expanding area, with applications ranging from cultural heritage to energy materials to advanced manufacturing. Negative muons are an excellent tool for determining the composition of a material, non-destructively, as a function of depth. EVA (Elemental, Visualisation and Analysis) is a new software package that is user-friendly and...
Typical time spectra measured in muon spin spectroscopy ($\mu$SR) are histograms of the detected positron times from one or multiple positron detectors as a function of time after implantation of the muon. In experiments at continuous muon beams, an online event logic is applied to the incoming streams of single detector hits [1,2]. Its two main purposes are (i) data reduction by multiple...
The current beta-NMR/beta-NQR spectrometers in ISAC-1 at TRIUMF constitute a unique research tool, enabling spin polarised ions (typically 8Li+) to be controllably implanted at a depth of between 5 – 200 nm within a material for investigations of thin films and artificial heterostructures. This involves decelerating 8Li+ beams through the generation of a “hill” in the electrostatic potential...
The D-line at the MUSE facility of the J-PARC MLF delivers high-intensity, spin-polarized muon beams of both positive and negative. Positive muons implanted into organic materials tend to form paramagnetic muoniated radicals at various sites, sometimes making it difficult to identify precise local environments. In contrast, negative muons are captured by atomic nuclei, resulting in...
Muonic x-ray has been used for an elemental analysis in various research fields. We have applied this technique to detecting metallic Li, which increases the risk to safety in a Li-ion battery. In our study, we found that metallic Li on the graphite anode can be detected with high sensitivity using muonic x-rays while less muon is captured by Li atoms in the anode.
Since metallic Li is...
The value of the nuclear charge radius depends on features of the nuclear structure such as the nuclear charge distribution, ρ, which has been systematically measured for almost all stable nuclei.
The nuclear charge radius can be mathematically defined using ρ, which in turn can be deduced from the X-ray transition energies of a muonic atom. The binding energy of the muonic atom is...
Surface treatments are an integral step in the preparation of superconducting radiofrequency (SRF) cavities fabricated using Nb, which are often used in particle accelerators. Common treatment approaches involve "baking" the metal in vacuum or a gaseous atmosphere at temperatures < 200 °C (see, e.g., [1]), causing light chemical doping of its subsurface up to depths of ~100 nm. As this...
Muon-Induced X-ray Emission (MIXE) is considered the only technique that allows for non-destructive elemental analysis of the bulk of a sample, with depth-profiling capabilities. Powered by the high-rate continuous muon beam from the Swiss Muon Source (S$\mu$S) at PSI, MIXE has undergone a remarkable revival [1] and has already demonstrated significant advancements [2–4]. To further strengthen...
The oxidative corrosion of steel in nuclear reactors is worsened by the removal of steel's passivizing oxide layer by flow-accelerated corrosion (FAC). Free radicals and hydrogen (H) species in feedwater greatly affect the rate of corrosion; film-forming amines (FFA) are therefore a candidate method to reduce FAC in the coolant systems of nuclear reactors by creating a barrier which limits the...
MnGe is a B20 cubic magnetic material observed to host nanoscale topological spin textures. Previous measurements by bulk µSR and small-angle neutron scattering have shown a 3-6 nm helimagnetic state below 200K and a possible 3D skyrmion lattice [1-3]. To further study this material, we have grown high quality crystalline MnGe thin films. With thickness of only a few helical wavelengths,...
GdNi$_4$B is currently one of the optimal magnetocaloric materials for hydrogen liquefaction, but the exact theoretical causes for that are unknown. GdNi$_4$B is a metallic compound exhibiting a ferromagnetic transition at around 50 K, below which they work as a magnetic refrigeration material. Therefore, their ferromagnetic structures should play a key role to determine their optimal magnetic...
We report $\mu$SR measurements on the layered triangular system NaYb$_{1-x}$Lu$_{x}$O$_{2}$ with $x$ = 0.05 and 0.15. We find the quantum disordered ground state [1,2] to be robust and insensitive to magnetic dilution, and exhibiting persistent spin dynamics down to the lowest temperature studied (T = 0.25 K). Indeed, the low temperature muon response is nearly identical to that found for...
A field-induced quantum spin liquid (QSL) state is an extraordinary phenomenon, hitherto unobserved in metallic frustrated compounds. CePdAl (CPA), a magnetically frustrated metallic compound with a kagome lattice, presents a unique opportunity to explore this phenomenon~\cite{Kitazawa1994}. Recent bulk measurements have revealed intriguing magnetic states in CPA when a magnetic field is...
By definition, properties of the S (superconducting) state are determined by Cooper pairs (CP). The pairs' mobility allows them to organize into a perfectly ordered lattice of microwhirls (MW) formed by the field induced currents in CPs, thereby reducing entropy of the pairs’ ensemble down to zero. The latter entails zero temperature of the ordered CPs, one of the consequences of which is zero...
Muonic X-ray Emission Spectroscopy is a non-destructive method of elemental analysis, which has recently been adopted several fields, such as cultural heritage. It is desirable to have a robust way of computationally modelling these experiments, to allow for simpler and more systematic identification of elemental X-ray intensities, particularly in samples consisting of multiple elements....
Muonium, a pure leptonic two-body system, is a powerful probe for precise QED tests and new physics searches. High-precision spectroscopy of muonium provides the best determination of the muon-to-electron mass ratio. For instance, muonium ground-state HFS microwave spectroscopy determined the mass ratio to 120 ppb [1]. Uncertainty in theoretical predictions for QED tests and new physics...
In order to make eco-friendly energy sources more widely available, there is an interest in manufacturing more efficient solar cells. This can be done by finding appropriate abundant materials that require less intensive production and typically at a lower cost. For this purpose, lead halide perovskites (APbX$_3$, A is an alkyl ammonium cation and X is a halide ion) have been researched...
Muon spin relaxation has been very successfully used to observe the dynamics in a range of materials, and electronic dynamics typically manifest themselves by showing a muon spin relaxation function which decays exponentially with time, with the rate of decay being related to the field autocorrelation function which can then be used to extract the dynamical parameters of the system [1]....
A novel domain wall architecture has recently been discovered in molecular crystals of the ferroelastic Mn³⁺ spin crossover compound [MnIII(3,5-diCl-sal₂(323))]BPh₄.[1] This complex exhibits a two-step thermal spin transition between the d⁴ spin triplet and spin quintet states, with a spin-state ordered phase forming at low temperatures. Single-crystal X-ray diffraction identified three...
AV$_3$Sb$_5$ (A = K, Cs,and Rb) V-based kagome metals have attracted significant attention owing to the intricate interplay between electronic correlations and nontrivial band topology, including features such as flat bands and van Hove singularities [1,2]. These systems host intertwined electronic instabilities [3], leading to a complex phase diagram between the charge density wave...
Hydrogen is known to degrade the performance of structural materials, a phenomenon commonly referred to as "hydrogen embrittlement". Hydrogen embrittlement is a well-known phenomenon in high strength materials and is responsible for subcritical crack growth in the material, fracture initiation and catastrophic failure with subsequent loss of mechanical properties such as ductility, toughness...
The magnetic excitation spectrum in a material of interest is governed by the interactions between spins within the lattice. Muon spin relaxation, beta detected nuclear magnetic resonance and the complementary technique of inelastic neutron scattering, among others, yield unique knowledge of the dynamic response of the system. However, the nature of the excitation spectrum at low energies...
Super-MuSR is a project to upgrade the MuSR beamline at ISIS to significantly increase its resolution and counting rate as part of the ISIS Endeavour programme of new and upgraded instruments. Here we report on project progress and component test results.
The beamline upgrade will add pulse slicing and spin rotation capabilities that increase the time resolution by a factor of ten and...
We present a study of the normal-state and superconducting properties of thin-film $\mathrm{Nb_{1-x}Ti_{x}N}$ using depth-resolved $^8$Li $\beta$-detected nuclear magnetic resonance ($\beta$-NMR). Spin-polarized $^8$Li$^{+}$ ions were implanted ~21 nm into a Nb$_{0.75}$Ti$_{0.25}$N(91 nm)/AlN(4 nm)/Nb sample, with their NMR response recorded at temperatures between 4.6 K to 270 K under a 4.1 T...
CaSb2 has been identified as a topological semimetal [1] and a bulk superconductor[2,3]. We investigate the superconducting state and the spontaneous magnetism using muon spin-relaxation (µSR) [4]. Zero-field muon relaxation shows little temperature dependence when the muon-spin is parallel to the c∗-axis, while an increase in relaxation appears below 1 K when the muon-spin is parallel to the...
The objective of the FAMU experiment is to carry out a precision measurement of the muonic hydrogen ground state hyperfine splitting (1S-hfs), with an unprecedented accuracy of the order of $10^{-5}$. This measurement would enable to extract the Zemach radius of the proton with an accuracy better than 1%, which will give precise insights on the structure of the proton, and play a crucial role...
The perovskite rare-earth R nickelates, RNiO$_3$, are the prototypical example of a metal-insulator transition in a strongly correlated metal. The transition can be tuned by choice of R, but LaNiO$_3$ remains a metal. In superlattices (SLs) with interlayers of LaAlO$_3$, LaNiO$_3$ can be driven insulating and antiferromagnetic if they are thin enough [1]. We used $^8$Li $\beta$-NMR, to study...
The ISIS muon beamlines have been operating for nearly 40 years and we have recently undertaken a phased programme of refurbishment. We give an overview of the work and performance improvements obtained.
The first muon beamline at ISIS started operation in 1987, and in 1993 the EMU and DEVA (now HIFI) ports were added. In 2013 we replaced the front end quadrupole doublet with a larger...
Vertex-reconstructed μSR (vx-μSR) leverages thin tracking detectors to record incoming muon and emitted positron trajectories, enabling unprecedented capabilities in spatially resolved spectroscopy. This approach overcomes critical limitations of conventional μSR at continuous beam facilities by operating at higher stopped muon rates (>400 kHz) and resolving sub-millimeter sample regions....
Fe$_3$GeTe$_2$ is a quasi-2D itinerant ferromagnet with a Van-der-Waals layered structure that exhibits substantial magnetic anisotropy. In bulk samples, this material becomes magnetically ordered below 200 K, although the low-temperature magnetic state for pure samples is debated, with some data suggesting a succession of two similar ferromagnetic states, and some suggesting a transition...
