Low temperature magnetic properties of NdCu2

μSR experiments on NdCu₂ give evidence for short range order below 25\ K above T_N=6.5\ K. No signal was detected between 16\ K and 1.2\ K where neutron scattering reveals an incommensurate spin structure. Below 1.2\ K the μSR signal is recovered and shows a rotation with 22 MHz. This is interpreted with a squaring up of Nd spins accompanied by a decrease of magnon excitations which is reflected in a decrease of damping of the muon signal. This revised version was published online in July 2006 with corrections to the Cover Date.     

Local magnetic field and muon site in CeAs

We report on zero field and longitudinal field μSR experiments on a CeAs single crystal between 3.3 and 12 K. Below the antiferromagnetic transition at 7.5 K a spontaneously precessing signal with a saturation frequency of \approx25 MHz representing the full sample amplitude has been found. From an analysis of the field dependence of the relaxation rate of this signal in \langle 100\rangle and \langle 110\rangle crystal orientation parallel to the muon spin and the applied longitudinal field, a \langle 100\rangle orientation of the local field at the muon site is concluded. This supports an AF‐I single‐\veck magnetic ordering. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

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.     

Spin alignment and Mössbauer hyperfine fields in the reentrant spin glass (Fe0.65Ni0.35)1-xMnx

Hyperfine Interactions - We performed Mössbauer spectroscopy on the ternary alloy system (Fe0.65Ni0.35)1-xMnx in applied external magnetic fields. From the hyperfine field distributions the...     

From antiferromagnetic order to static magnetic stripes: the phase diagram of (La,Eu)2-xSrxCuO4

The magnetic order of (La,Eu)2-xSrxCuO4 ( x相似文献   

The magnetic phases and structures of Ce(Ru1-xFex)2Ge2 studied by μ-SR

We report on the structures of the magnetic phases of CeRu₂Ge₂ and their evolution in the series Ce(Ru_1-xFe_x)₂Ge₂. The crossover behavior between the ferromagnetic ground state of CeRu₂Ge₂ to the paramagnetic ground state of CeFe₂Ge₂ is compared to the behavior in the series CeRu₂(Ge_1-xSi_x)₂. A profound difference is observed between these two series, which is in contradiction to the uniform behavior predicted by the Doniach-necklace model. This revised version was published online in August 2006 with corrections to the Cover Date.     

Dynamic short-range order observed in the (Zn)[Fe2]O4 spinel by neutron diffraction, μSR,and Mössbauer experiments

Using neutron diffraction (ND), muon-spin rotation/relaxation (SR), and⁵⁷Fe-Mössbauer spectroscopy (MS) we have investigated magnetic properties of the normal spinel (Zn)[Fe₂]O₄. In compounds which are slowly cooled from 1200°C to room temperature inversion is below detection limits. AtT _N = 10.5 K the spinel exhibits long-range antiferromagnetic order (LRO). The transition as seen in thermal-scan spectra by MS is very sharp. However, ND andSR experiments show that already at temperatures of 10T _N a short-range antiferromagnetic ordering (SRO) develops which extends through 70% of the sample volume just aboveT _N . BelowT _N SRO and LRO coexist. At 4.2 K still 25% of the sample is short-range ordered. The regions over which the SRO extends have a size of 3 nm. Their fluctuation rates are in the GHz range. Modern ab initio cluster calculations successfully describe the magnetic hyperfine fields as well as the electric field gradient (EFG) tensor at the Fe sites. Covalency of the Fe-O and Zn-O bonds is important. The physical origin of the regions exhibiting SRO, however, remains unresolved at this point.     

μSR on an induced‐moment spin glass system: Hg1-xFexSe

Zero and longitudinal field μSR have been used to examine the singlet ground state magnetism of the diluted magnetic semiconductor Hg_1-xFe_xSe. For x\geq 0.05\ μSR experiments indicate spin glass behaviour which is limited to sample regions with locally enhanced Fe²⁺ content. Longitudinal field spectra in the glassy state reveal a static local field \sim 50 mT due to induced moments of Fe²⁺. These are proposed to originate from a distribution of bound magnetic polaron energies. This revised version was published online in July 2006 with corrections to the Cover Date.