arXiv subjects

W. Hayes

Publications and source records attributed to W. Hayes.

25 records · Page 2Linked to original sources

arXiv2006

Magnetism in the S=1 frustrated antiferromagnet GeNi2O4 studied using implanted muons

We present the results of a muon-spin relaxation study of GeNi2O4. We provide further clarification of the two transitions to the antiferromagnetic state and measure the magnetic field dependence of the heat capacity up to 14 T. Both oscillatory and relaxing signals are observed below the lower transition (at temperature $T_{N2}) in the muon-decay positron asymmetry spectra, arising from two distinct types of magnetic environment. A possible explanation is suggested in terms of the separate ordering of two magnetic subsystems, one of which does not order fully down to the lowest measured temperature.

cond-mat.str-el↗

arXiv2005

Thermodynamic and magnetic properties of the layered triangular magnet NaNiO2

We report muon-spin rotation, heat capacity, magnetization, and ac magnetic susceptibility measurements of the layered spin-1/2 antiferromagnet NaNiO2. These show the onset of long-range magnetic order below T_N = 19.5K. Rapid muon depolarization persisting to about 5K above T_N is consistent with the presence of short-range magnetic order. The temperature and frequency dependence of the ac susceptibility suggests that magnetic clusters persist above 25K in the paramagnetic state and that their volume fraction decreases with increasing temperature. A frequency dependent peak in the ac magnetic susceptibility at T_sf = 3K is observed, consistent with a slowing of spin fluctuations at this temperature. A partial magnetic phase diagram is deduced.

cond-mat.str-el↗

arXiv2005

Unconventional magnetic properties of the weakly ferromagnetic metal BaIrO_3

We present experimental evidence for small-moment magnetism below the ferromagnetic transition temperature (T_c3 = 183 K) in the quasi-one-dimensional metal BaIrO_3. Further, we identify rearrangement of the local magnetic moment distribution, which leaves the bulk magnetization unchanged, at the Mott-like transition (T_c1 = 26 K). These results are only possible via muon-spin relaxation ($μ$SR) techniques, since neutron scattering studies are hindered by the large absorption of neutrons by Ir. The low temperature characteristics of this compound, as revealed by $μ$SR, are unconventional, and suggest that its magnetic properties are driven by changes occuring at the Fermi surface due to the formation of a charge-density wave state.

cond-mat.str-el↗

arXiv2004

Magnetic phase separation in EuB6 detected by muon spin rotation

We report results of the first muon-spin rotation measurements performed on the low carrier density ferromagnet EuB$_6$. The ferromagnetic state is reached via two magnetic transitions at $T_{\rm m}=16.5$ K and $T_{\rm c}=12.6$ K. Two distinct components are resolved in the muon data, one oscillatory and one non-oscillatory, which arise from different types of magnetic environment, and we have followed the temperature dependence of these components in detail. These results provide evidence for magnetic phase separation and can be interpreted in terms of the gradual coalescing of magnetic polarons.

cond-mat.str-el↗

arXiv2004

Experimental demonstration of a new radiation mechanism: emission by an oscillating, accelerated, superluminal polarization current

We describe the experimental implementation of a superluminal ({\it i.e.} faster than light {\it in vacuo}) polarization current distribution that both oscillates and undergoes centripetal acceleration. Theoretical treatments lead one to expect that the radiation emitted from each volume element of such a polarization current will comprise a Čerenkov-like envelope with two sheets that meet along a cusp. The emission from the experimental machine is in good agreement with these expectations, the combined effect of the volume elements leading to tightly-defined beams of a well-defined geometry, determined by the source speed and trajectory. In addition, over a restricted range of angles, we detect the presence of cusps in the emitted radiation. These are due to the detection over a short time period (in the laboratory frame) of radiation emitted over a considerably longer period of source time. Consequently, the intensity of the radiation at these angles was observed to decline more slowly with increasing distance from the source than would the emission from a conventional antenna. The angular distribution of the emitted radiation and the properties associated with the cusps are in good {\it quantitative} agreement with theoretical models of superluminal sources once the effect of reflections from the earth's surface are taken into account.

physics.optics↗

arXiv2002

The pressure dependence of many-body interactions in the organic superconductor $κ$-(BEDT-TTF)$_{2}$Cu(SCN)$_{2}$: A comparison of high pressure infrared reflectivity and Raman scattering experiments

We determine the pressure dependence of the electron-phonon coupling in $κ$-(BEDT-TTF)$_{2}$Cu(SCN)$_{2}$ by comparison of high pressure Raman scattering and high pressure infrared (IR) reflectivity measurements. The Raman active molecular vibrations of the BEDT-TTF dimers stiffen by 0.1-1 %GPa$^{-1}$. In contrast, the corresponding modes in the IR spectrum are observed at lower frequency, with a pressure dependence of 0.5-5.5 %GPa$^{-1}$, due to the influence of the electron-phonon interaction. Both dimer charge-oscillation and phase-phonon models are employed to extract the pressure dependence of the electron molecular-vibration coupling for these modes. Analysis of our data suggests that the reduction of electron-phonon coupling under pressure does not account for the previously observed suppression of superconductivity under pressure and that electron-electron interactions may contribute significantly to the pairing mechanism.

cond-mat.str-el↗

arXiv2001

The pressure dependence of electron-phonon coupling in the organic superconductor $κ$-(BEDT-TTF)$_{2}$Cu(SCN)$_{2}$: A comparison of high pressure infrared reflectivity and Raman scattering experiments

We determine the pressure dependence of the electron-phonon coupling constant in $κ$-(BEDT-TTF)$_{2}$Cu(SCN)$_{2}$ by comparison of high pressure Raman scattering and high pressure infrared reflectivity (IR) measurements. We use comparison of the IR reflection spectrum from deuterated and protonated samples to aid the deconvolution of several overlapping phonon modes. These coupled modes are modelled with a Green's function to extract the linear pressure dependence of the individual modes. The Raman active molecular vibrations of the BEDT-TTF dimers stiffen by 0.1-1 %GPa$^{-1}$. In contrast, the corresponding modes in the IR spectrum are observed at lower frequency, with a pressure dependence of 0.5-5.5 %GPa$^{-1}$, due to the influence of the electron-phonon interaction. The stronger pressure dependence of the central C=C mode of the BEDT-TTF molecule in the IR, is discussed. Our analysis suggests that reduction of electron-phonon coupling under pressure does not account for observed suppression of superconductivity under pressure.

cond-mat.str-el↗