Depolarization in reentrant spin glasses: a comparison between neutron and muon probes

In the amorphous ( Fe_1-x Mn_x)₇₅ P₁₆ B_6 Al_3 alloys, muon and neutron depolarization data, combined with the results of small angle neutron scattering, magnetization and Mössbauer spectroscopy, probe the existence of three distinct magnetic transitions at T_C, T_K and T_F (T_F < _K < _C).     

Spin fluctuations and magnetic order in the heavy fermion compound CePt2Sn2

We present zero and longitudinal field μ SR measurements of single crystal and polycrystalline specimens of the heavy fermion compound CePt₂Sn₂. Above 1 K the behaviour of the two samples is indistinguishable; the muon 1/T_1 increases with decreasing temperature until 25 K when it plateaus. The 1/T_1 relaxation rate differs strongly for the two cases below \sim\,0.8\ K. At 0.1 K a rate of about 20 μ s^-1 is seen in the polycrystal while in the single crystal it is only about 5 μ s^-1. Even more revealing is the fact that longitudinal field decoupling spectra at very low temperatures demonstrate an essentially static spin system to be present in the polycrystalline material while the single crystal shows definite dynamic spin properties. We conclude that, in the presence of the distortion, long range magnetic order occurs below 0.9 K while in tetragonal symmetry long range order is suppressed (probably due to frustration) and spin fluctuations remain for T\rightarrow0. This revised version was published online in July 2006 with corrections to the Cover Date.     

La2-xSrxCu1-yZnyO4: Tc and ns/m* correlations seen with muon spin rotation

We report the muon spin rotation experiments on Zn substituted La_1-x Sr_x CuO₄, for four zinc concentrations y=0.0,0.0025,0.005,0.01, at strontium concentrations x=0.15,0.20. We find that T_ c in the optimally doped (x=0.15) and overdoped (x=0.20) 2:1:4 decreases linearly with increasing zinc concentration. Plotted against the planar zinc concentration, the T_c’s of both series seem to fall on the same line. The superconducting carrier density/effective mass ratio, n_ s/m^*, at first decreases linearly, rising above this line for higher zinc concentrations. This behavior may result from the localization of carriers in an area \xi_ab around each zinc atom. This revised version was published online in August 2006 with corrections to the Cover Date.     

Magnetic order in La2-x Bax CuO4 and La1.6-x Nd0.4 Srx CuO4 for x=0.125

We present μSR experiments on La_2-x Ba_x CuO₄ and La_1.6-x Nd_0.4 Sr_x CuO₄ for x=0.125. Both of these materials order magnetically with T_N\approx30\ K, while a superconducting sample of La_1.4 Nd_0.4 Sr_0.2 CuO₄ showed no evidence for static copper moments. Our results support the conclusion that the so‐called “1/8” anomaly in La_2-x Ba_x CuO₄ is a result of static (pinned) charge segregation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Spin freezing in geometrically frustrated β-Mn probed by muon spin relaxation

Muon spin relaxation was measured down to 0.05 K on a geometrically frustrated metallic system, β-Mn. The observed relaxation rate increases with decreasing temperature and unexpectedly makes a peak at 0.5 K indicating a spin freezing below the temperature. Actually the asymmetry is almost recovered by applying a longitudinal magnetic field of 0.1 T. But since the tail amplitude is more than half and the dynamical relaxation is still appreciable at the lowest temperature, it is likely that the frozen moments are associated with imperfection as oxygen impurity and the intrinsic ground state is fluctuating spin liquid. This revised version was published online in August 2006 with corrections to the Cover Date.     

μSR studies of Li‐doped La2CuO4

Magnetic properties of the Li‐doped cuprates La₂Cu_1-xLi_xO₄ (where x=0.01,\ 0.05,\ 0.10,\ 0.45, and 0.50) have been studied by μSR. For low Li concentrations (x\Eleq 0.10) we find a rapid suppression of T_N as x increases, but little change in the magnitude and temperature dependence of the AFM order parameter. This indicates that Li doping effectively destroys AFM (similar to Sr doping, but different from Zn doping) without strongly affecting the onsite Cu moments and the shape of the spinwave excitation spectrum. For high Li concentrations we find magnetic clusters in about 15% of the sample volume; the remaining volume is non‐magnetic, suggesting possible singlet‐state formation. This revised version was published online in July 2006 with corrections to the Cover Date.