Muon spin relaxation in solid3He

Muon spin relaxation in solid³He depends non-monotonously on the temperature. It is shown that this is entirely due to the magnetic dipole-dipole interactions. The observed line narrowing cannot be explained by the mechanism of positive charge hopping described by an Arrhenius-like law. The relaxation rate at low temperatures was found to increase under the influence of an external electric field.     

Muon spin relaxation in ferromagneticPdMn

Positive-muon ( ⁺) spin relaxation experiments have been carried out in the dilute ferromagnetic alloy Pd+2 at.% Mn (T _c=5.8 K). In the paramagnetic state the inhomogeneous ⁺ linewidth is proportional to the bulk magnetization. BelowT _c the ⁺ linewidth and the width of the ⁺ local field distribution in zero applied field are both in qualitative accord with the Sherrington-Kirkpatrick theory of disordered magnets.This work was performed under the auspices of the U.S. Department of Energy, and was supported by the U.S. National Science foundation, grant nos. DMR-7909223 and DMR-8115543, and by the Netherlands Stichting voor Fundamenteel Onderzoek der Materie (FOM).     

Muon spin relaxation in heavy fermion systems

Heavy fermion systems have received a great deal of study by a wide variety of techniques, includingSR. In a number of systems, coexisting superconducting and magnetic states have been reported, leading to speculation of an intimate connection between magnetism and superconductivity in these compounds. We observe a spontaneous magnetic field in the superconducting phase of UPt₃. In addition, the broadening of the transverse field muon precession signal only onsets approximately 60 mK below the superconductingT _c. Our results provide evidence that the lower superconducting phase in theH-T phase diagram of UPt₃ is characterised by broken time-reversal symmetry. Measurements of URu₂Si₂ and CeCu_2.2Si₂ indicate that the magnetically ordered volume fraction is temperature dependent in both systems.     

Muon spin relaxation and superconducting critical currents

Effect of pinning on muon spin relaxation is discussed. The application of μSR to study of the second type superconductors are considered.     

Muon spin relaxation and knight shift in the heavy-fermion superconductor UPt3

Positive muon spin relaxation experiments have been conducted on the heavy-fermion superconductor UPt₃ in both the normal and superconducting states for zero, transverse, and longitudinally applied magnetic fields. Below 6 K in zero applied field, the μ⁺ relaxation rate is approximately twice that expected from¹⁹⁵Pt nuclear dipolar relaxation alone. Transverse- and longitudinal-field measurements show that the observe relaxation rate depends on magnetic field and is quasistatic in origin. It is suggested that the onset of very weak (≈10⁻³ μ_B/U atom) magnetic ordering below approximately 6 K is responsible for the observed increase in the relaxation rate. μ⁺ Knight shift measurements in the normal state of UPt₃ show a temperature dependent shift K_μ which tracks the bulk susceptibility X. From the K_μ vs. X plot, a μ⁺ hyperfine field of approximately 100 Oe/μ_B is extracted.     

Muon spin relaxation in different samples of DyAl2

Two samples of DyAl₂ were studied by longitudial μSR in the paramagnetic and ferromagnetic regime. In a region T_c±40 K the samples give different signals although X-ray analysis can not detect any impurity phase in either of them.     

Muon spin relaxation measurements of spin-correlation decay in spin-glassAgMn

The field (H) dependence of the muon longitudinal spin-lattice relaxation rate well below the spin glass temperature inAgMn is found to obey an algebraic form given by (H) ^v –1 withv=0.54±0.05. This suggests that Mn spin correlations decay with time ast ^–v , in agreement with mean field theories of spin-glass dynamics which yieldv0.5. Near the glass temperature the agreement between the data and theory is not as good.We are grateful to C.E. Olsen for preparing the samples, C. Boekema, S.A. Dodds, G.A. Gist, R.L. Hutson, S.L. Rudaz and A. Yaouanc for help during the experiments and to D.L. Huber and R.E. Walstedt for useful discussions. This work was performed under the auspices of the U.S. Department of Energy and was also supported by the U.S. National Science Foundation, Grant No. DMR-8115543.     

Muon spin relaxation in diluted triangular‐lattice antiferromagnet

Zero and longitudinal field μSR measurements on diluted triangular‐lattice antiferromagnet LuFeMgO₄ have revealed gradual and highly anisotropic slowing‐down of spin fluctuation. Relaxation rate \lambda in the condition with initial muon spins perpendicular to the hexagonal c‐plane shows divergent behavior while that in the parallel configuration remains finite. At certain temperature range the fluctuation of spins is suppressed by a small external magnetic field. Monte Carlo calculation suggests that the correlation time for z(c)‐component of spins diverges first on cooling. This revised version was published online in July 2006 with corrections to the Cover Date.     

Muon spin relaxation studies in frustrated and/or low-dimensional spin systems

An overview is given on muon spin relaxation (SR) measurements in frustrated and/or low dimensional spin systems. In the frustrated Kagomé lattice system SrCr₈Ga₄O₁₉, we observed dynamic spin fluctuations of 30 GHz, without any static frozen component even atT=0.1 K, much below the susceptibility-cusp temperatureT _g=3.5 K. This is in clear contrast with the case in dilute-alloy spin glassesCuMn andAuFe, where static order develops belowT _g. We also present the dimensionality dependence of the sub-lattice magnetization curves in 2-d Heisenberg systems, the remarkable suppression of the ordering temperature in a 1-d system Sr₂CuO₃, the observation of activation type spin dynamics in a 1-d Ising ferromagnet (DMeFc)(TCNE) aboveT _c, slow spin fluctuations ( 60 MHz) in Haldane-gap systems at low temperatures, and some results from organic 1-d and 2-d magnetic systems.     

Muon spin relaxation studies of magnetic-field-induced effects in high-Tc superconductors

Muon spin relaxation measurements in high transverse magnetic fields [FORMULA: SEE TEXT] revealed strong field-induced quasistatic magnetism in the underdoped and Eu-doped (La,Sr)2CuO4 and La1.875Ba0.125CuO4, existing well above Tc and TN. The susceptibility counterpart of Cu spin polarization, derived from the muon spin relaxation rate, exhibits a divergent behavior towards T approximately 25 K. No field-induced magnetism was detected in overdoped La1.81Sr0.19CuO4, optimally doped Bi2212, and Zn-doped YBa2Cu3O7.     

Muon spin relaxation by electronic excitations moving in one dimension

The manner in which an electronic spin, executing a linear random walk, e.g. along a polymer chain, depolarizes a muon (or proton) probe spin, is investigated by computer simulation. The essential features of the model are the assumptions of a contact hyperfine interaction with limited range and of loss of coherence between successive encounters. The low dimensionality of the motion is reflected in the shape of the relaxation functions generated, which depart significantly from simple exponentials. Fits to various functional forms are examined for different combinations of hop rate and chain length, hyperfine constant and applied magnetic field. This revised version was published online in August 2006 with corrections to the Cover Date.     

Muon spin relaxation in Li0.6TiO2 anode material

In Li_0.6TiO₂ the longitudinal muon spin relaxation function has been measured for temperatures between 10 and 600 K. The μSR spectra were analyzed with a Markov process for multiple collisions. The time scale found for the Li⁺ diffusion is of the order of the microsecond or shorter. Above T = 100 K the magnetic field distribution at the muon is decreasing with increasing temperature.     

Muon spin relaxation studies of extremely concentrated paramagnetic electrolyte solutions

The diamagnetic signal in aqueous solutions of non-reacting salts arises from muons substituted for protons in water molecules. For concentrated solutions of paramagnetic salts, muon spin relaxation results from the strong dipolar and scalar interactions between the paramagnetic ion and the muon. Information on dynamic and structural aspects of such solutions is derived from measurements of the transverse relaxation rate as a function of applied field over a wide range. Data are presented for concentrated solutions of Mn(NO₃)₂ and solutions of composition Mn _x Ca_(1–x (NO₃)₂·6H₂O.     

Muon spin relaxation in a spin glass CuMn observed in finite longitudinal magnetic fields

Muon spin depolarization in a spin glass CuMn (1.1 at.%, T_g = 10.8 K) has been observed in longitudinal external magnetic fields H_L = 0–640 Oe. The depolarization rate did not depend on H_L at T > T_g, reflecting a fast dynamical fluctuation of Mn moments. In contrast, a remarkable field dependence was observed below T_g. Static and dynamical local fields on μ⁺ from Mn moments were found to coexist at T ～ 0.9 T_g. The results suggested a rapid change of spin dynamics around T_g.