Spin dynamics in the reentrant spin glass ( Fe0.65 Ni0.35)1-x Mnx

The spin dynamics in the reentrant spin glass ( Fe_0.65 Ni_0.35)_1-x Mn_x has been studied by zero, longitudinal and transverse field μSR. In the ferromagnetic reentrant and pure spin glass regimes (x\leqslant 0.175), zero field experiments reveal a stretched exponential muon relaxation with a universal behaviour of the dynamic exponent \beta above the spin glass transition. There are no qualitative differences between the ferromagnetic and paramagnetic phases. In transversal field μSR experiments the divergence of the relaxation rate close to the spin glass transition is suppressed for manganese doping up to x=0.113 but enhanced for slightly higher doping (x\geqslant 0.12). We understand this behaviour as a crossover from an itinerant to a more localized state of the 3d electron system. This is also supported by the fact that in the highly doped regime with dominant antiferromagnetic interactions the muon relaxation rate diverges above the antiferromagnetic transition temperature. This revised version was published online in July 2006 with corrections to the Cover Date.     

Mössbauer studies of polymers in the glassy state and near their glass transition

Mössbauer absorption spectra of glassy block and copolymers with lowT _G containing ferrocene have been recorded in a wide temperature range (4–330 K) to investigate the dynamical processes of the system, in the glassy state and around the glass transition. An inhomogeneous broadening due to conformational substates with different hyperfine parameters found at lower temperatures becomes motionally narrowed above 40 K. Whereas in the glassy state both the block and the copolymers reveal the same vibrational behaviour, we found differences in the vicinity of their respective glass transitions. For the block polymer an anomalous decrease of the recoilfree fractionf _A was found above the static glass transition. In agreement with neutron data on other polymers we attribute this behaviour to an onset of motions of the ferrocene units of higher than 10¹⁰ Hz. For the copolymers, however, a departure of lnf _A from linearity was detected already far below the staticT _G. We propose that this is caused by residual solvents which allow an easier cooperative rearrangement of the segments even belowT _G. First attempts to interpret the Mössbauer data by means of the predictions of the mode coupling theory are reported.     

High pressure studies of actinide intermetallics

Hyperfine Interactions - Magnetic properties of NpOs2,NpAl2. NpCo2Si2, NpAs, and NpSn3 are investigated by high pressure Mössbauer spectroscopy using the 60 keV transition in237Np. A wide...     

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.     

μSR on the novel heavy‐fermion system Nd2-yCeyCuO4

The magnetic correlations in Nd_2-yCe_yCuO₄ have been studied by zero and longitudinal field μSR. Nd_1.8Ce_0.2CuO₄ reveals a saturation of the muon relaxation rate below 0.5 K. Even down to 70 mK LF spectra evidence spin fluctuations in the dynamic regime with a rate of \sim 10⁹ s^-1 excluding long range magnetic order or spin glass freezing. The average Nd moment is estimated to be \approx 0.2\mu_B, i.e., strongly reduced from the value determined for the ground state Kramers doublet of Nd₂CuO₄. Extending former μSR measurements on Nd₂CuO₄, a gradual enhancement of the internal field has been detected below 10 K which is accompanied by an increase of the relaxation rate. These results are attributed to the development of ordered Nd moments. This revised version was published online in July 2006 with corrections to the Cover Date.     

Detection of human metabolites using multi-capillary columns coupled to ion mobility spectrometers

The human breath contains indicators of human health and delivers information about different metabolism processes of the body. The detection and attribution of these markers provide the possibility for new, non-invasive diagnostic methods. In the recent study, ion mobility spectrometers are used to detect different volatile organic metabolites in human breath directly. By coupling multi-capillary columns using ion mobility spectrometers detection limits down to the ng/L and pg/L range are achieved. The sampling procedure of human breath as well as the detection of different volatiles in human breath are described in detail. Reduced mobilities and detection limits for different analytes occurring in human breath are reported. In addition, spectra of exhaled air using ion mobility spectrometers obtained without any pre-concentration are presented and discussed in detail. Finally, the potential use of IMS with respect to lung infection diseases will be considered.     

Magnetic properties of UN studied by μSR

In the paramagnetic range (T>T _N=53 K) fluctuations of the moments on uranium are too fast to produce a sizeable damping of the SR signal even close toT _N. This rules out the formation of a magnetic precursor state as seen in UAs. In the antiferromagnetic regime all contributions to the field at the muon site cancel due to symmetry. Comparison with analogous data on other uranium mono-pnictides show that the magnitude of the field distribution width in the type I-single k antiferromagnetic state is not an intrinsic property of these materials.Work supported by the German Federal Minister for Research andTechnology (BMFT) under contract number 03-KA2-TUM-4.