Field Muon Spin Relaxation Research Articles

Quantum diffusion of positive muon in pure tantalum

Quantum diffusion of positive muons has been studied in high purity Ta by zero and longitudinal field muon spin relaxation techniques. We found that the muon hopping rate in Ta is more or less the same as in pure Cu (i.e., \nu\simeq105\sim106\ s™1), showing a characteristic temperature dependence proportional to T™\alpha with \alpha ranging from 2 to 0.2 below 20 K. In addition, a step‐like change of the nuclear dipolar width was observed at 60 K associated with the sharp peak of hopping rate, suggesting a change of stable muon sites.

Probing the Spin-Spin Dynamical Autocorrelation Function in a Spin Glass above Tg via Muon Spin Relaxation.

We report zero and longitudinal field muon spin relaxation measurements in the metallic spin glass AgMn(0.5 at. %) at $Tg{T}_{g}$. We find that muon polarization obeys a time-field scaling relation which allows us to distinguish between three possible forms of the spin-spin dynamical autocorrelation function: a power law, a stretched exponential, and a cutoff power law. We also discuss the evolution of the muon relaxation line shape as the temperature approaches ${T}_{g}$.

Zero-field muon spin lattice relaxation rate in a Heisenberg ferromagnet at low temperature.

We provide a theoretical framework to compute the zero field muon spin relaxation rate of a Heisenberg ferromagnet at low temperature. We use the linear spin wave approximation. The rate, which is a measure of the spin lattice relaxation induced by the magnetic fluctuations along the easy axis, allows one to estimate the magnon stiffness constant.

Absence of zero field muon spin relaxation induced by superconductivity in the B phase of UPt 3

We present muon spin relaxation measurements performed on crystals of the heavy fermion superconductor UPt 3. In zero applied field, contrary to a previous report, we do not observe an increase of the internal magnetic field in the lower superconducting phase (the B phase). Our result gives an experimental upper bound of the magnetic field that could be associated with the superconducting state.

Zero Field Muon Spin Relaxation Study of the Low Temperature State inα-(BEDT-TTF)2KHg(SCN)4

Zero field muon spin relaxation measurements are reported for the low temperature magnetic phase of the organic metal (BEDT-TTF${)}_{2}$KHg(SCN${)}_{4}$. Steplike changes in the relaxation rate indicate two transitions; the first occurs around 12 K and is accompanied by a change in the shape of the relaxation function. A further increase in the relaxation rate occurs below 8 K. These changes signify the onset of an internal magnetic field distribution below the transition, which is assigned to a spin-density-wave (SDW) ordering with an estimated amplitude of $\ensuremath{\sim}3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}{\ensuremath{\mu}}_{B}$ below 8 K. This very small value is consistent with the upper limits set by previous magnetic resonance studies and also with a simple mean field description of the SDW transition.

Unusual static local field distribution in the spin-frozen state of icosahedral AlMnSi

Zero-field and longitudinal field muon spin relaxation in AlMnSi quasicrystals show the spin glass state remains inhomogeneous down to temperatures of order 1 100 T g . In the frozen-moment regions, the field distribution at the muon site is static but causes monotonic relaxation of the ensemble polarization to the “ 1 3 tail ”.

Zero-field μSR study of CeRu2Si2 heavy fermion compound

Zero — field muon spin relaxation measurements have been carried out on a high-quality single-crystal sample of the paramagnetic heavy-fermion compound CeRu2Si2 from 5K to 300K. The observed relaxation at each temperature was well fitted by a function described by the product of a Kubo-Toyabe type and an exponential one. The temperature dependence of the Kubo-Toyabe relaxation rate σZF shows an almost constant value (0.03 μs−1) which is comparable to the calculated linewidth due to nuclear dipole fields from99Ru and101Ru atoms assuming the possible μ+ stopping sites for the ThCr2Si2 structure. On the other hand, we observed an increase of the exponential relaxation rate λZF to a value of ∼- 0.02 μs−1 with decreasing temperature below about 100K. This suggests a contribution of Ce 4f moments.

Muon spin relaxation measurements in kagomé lattice system SrCr8Ga4O19

Dynamical spin fluctuations in SrCr8−xGa4+xO19 a frustrated spin system on a kagome lattice, is examined by the longitudinal field muon spin relaxation technique. This system shows a spin-glass (SG)-like cusp in the susceptibility atTg=3.5(2) K. The slowing down of Cr spin fluctuations is found to occur over a very wide temperature rangeTg<T<30Tg. AsT/Tg → 0 these fluctuations remain without static polarization (order parameter). Such strong fluctuations belowTg have not been observed before in a conventional SG system.

Static magnetic order in La 1.875Ba 0.125CuO 4

Zero field muon spin relaxation measurements of high quality, single phase La 1.875Ba 0.125CuO 4 indicate that this system exhibits static magnetic order below 38 K. At this x = 1 8 concentration, superconductivity is suppressed. The ordered spins most likely reside on the copper sites.

Fluctuation of rare-earth atom magnetic moments in superconducting ceramics (Ho,Er)-Ba-Cu-O studied by μSR

Zero field muon spin relaxation measurements of the ceramic high-Tc superconductors HoBa2Cu3O7-σ, Oc≃93 K) and ErBa2Cu3O7-σ (Tc≃95 K) reveal the sharp difference between the behaviours of the muon spin relaxation rate at temperatures below 20K. This fact may be explained by assumption that the frequency of fluctuations of Er magnetic moments exceeds by far the fluctuation frequency of Ho in 1-2-3 compounds.

Positive muons in bismuth: determination of their sites, detection of a large local lattice contraction and giant associated electric field gradients, evidence for short and long range diffusion

Using a high purity Bi single crystal the temperature and orientation dependence of the zero and transverse field muon spin relaxation rate has been studied in detail. The results imply that the μ+ occupies one of the two possible interstitial sites in the distorted rhombohedral crystal structure of Bi below 10 K and the other site above 80 K. At both sites the nearest neighbor Bi atoms are found to be shifted towards the μ+ by ≈10% of their nominal distance, implying a large local lattice contraction. In concomitance extremely strong electric field gradients are manifest at the nn Bi nuclei. An almost temperature independent reduced relaxation rate in the temperature range from 20 K to 60 K is interpreted in terms of short range diffusion along a limited chain of alternating types of sites. Above 100 K both long range and short range diffusion are indicated.

Muon diffusion in pure bismuth: Evidence for an extended muonic state

The diffusion of positive muons (μ +) in ultra-pure monocrystalline bismuth has been studied experimentally by the method of zero and low longitudinal field muon spin relaxation (ZF-, LLF-μSR). The results indicate that the conventional interpretation of the spin rotation spectrum by simple motional narrowing does not hold at low temperature in this system. Existence of an extended state (which is metastable) is proposed on the basis of an analysis using a two-state model of diffusion.

Zero field muon spin relaxation in simple magnets and spin glasses

A theory is developed for the calculation of zero field muon spin relaxation function for classical simple magnets (Ising, XY, and Heisenberg) in D(=1,2,3) dimensions. The results are different from the Kubo-Toyabe theory, except for Heisenberg system in three dimension. Relation between the relaxation function and random field distribution is dicussed and a new method of analysing experimental data is suggested and discussed in the context of spin glasses.

Zero field muon spin relaxation rate in the superconducting state of Nb3Al

It was shown that at T=12 k the dipole relaxation of a positive muon in Nb3Al in the zero external magnetic field is well described by the Kubo-Toyabe function for the static distrubution of the dipole magnetic fields in the absence of muon diffusion. The superconducting state of Nb3Al was used for eliminating the background from muons stopped in the cryostat walls.

Study of the hybrid state of Y 9Co 7(2.0≲ T≲ 6 K) by means of zero field muon spin relaxation

Muon spin relaxation functions were measured in the magnetic superconductor Y 9Co 7 for T ≳ 2.0 K and at zero applied field. In the paramagnetic region ( T ≳ 6.0 K) the depolarization of the muon spins is due to the quasi-static 59Co nuclear moments. The onset of the magnetic state results in a fast-relaxing signal that corresponds to dipolar fields of the order of 100 0e; this component grows steadily in amplitude as the material transists from the hybrid into the superconducting state. The data are consistent with the high degree of inhomogeneity of the (not long-range) ordering and coexisting but non-competing magnetic and superconducting properties in the “hybrid” state (2< T<5K).

Precise measurement of low temperature diffusion of positive muons in Cu: Evidence for the effect of muon-electron interaction in metals

The diffusion rate of positive muons in high purity Cu was measured by means of the zero field muon spin relaxation method for temperatures from 69 mK to 135 K. We found that with decreasing temperature the rate reaches a minimum at around 20 K and increases down to 0.5 K, where it clearly levels off. The origin of the observed temperature dependence is discussed in the light of recently developed theories taking into account the μ +-conduction electron interaction in metals, where the basic coupling constant K is determined to be 0.32.