Magnetic, thermodynamic, and electrical transport properties of the noncentrosymmetric B20 germanides MnGe and CoGe

We present magnetization, specific heat, resistivity, and Hall effect measurements on the cubic B20 phase of MnGe and CoGe and compare to measurements of isostructural FeGe and electronic structure calculations. In MnGe, we observe a transition to a magnetic state at $T_c=275$ K as identified by a sharp peak in the ac magnetic susceptibility, as well as second phase transition at lower temperature that becomes apparent only at finite magnetic field. We discover two phase transitions in the specific heat at temperatures much below the Curie temperature one of which we associate with changes to the magnetic structure. A magnetic field reduces the temperature of this transition which corresponds closely to the sharp peak observed in the ac susceptibility at fields above 5 kOe. The second of these transitions is not affected by the application of field and has no signature in the magnetic properties or our crystal structure parameters. Transport measurements indicate that MnGe is metal with a negative magnetoresistance similar to that seen in isostructural FeGe and MnSi. Hall effect measurements reveal a carrier concentration of about 0.5 carriers per formula unit also similar to that found in FeGe and MnSi. CoGe is shown to be a low carrier density metal with a very small, nearly temperature independent diamagnetic susceptibility.Comment: 16 pages 23 figure

High order harmonic generation from SF6: Deconvolution of macroscopic effects

Citation: Wilson, B. P., Fulfer, K. D., Mondal, S., Ren, X., Tross, J., Poliakoff, E. D., . . . Trallero-Herrero, C. (2016). High order harmonic generation from SF6: Deconvolution of macroscopic effects. Journal of Chemical Physics, 145(22), 11. doi:10.1063/1.4971244We measure high order harmonics from the molecule SF6 over a large range of phase matching conditions and observe several features in the harmonics that are largely independent of such macroscopic conditions. The experimental data are then compared to the quantitative rescattering theory for the generation of harmonics from three orbitals. With this comparison, we are able to assign spectroscopic features in the harmonics to contributions from 1t(1g) (HOMO) and 5t(1u) (HOMO-1) orbitals. Published by AIP Publishing

Atomic photoionization experiment by harmonic-generation spectroscopy

Citation: Frolov, M. V., Sarantseva, T. S., Manakov, N. L., Fulfer, K. D., Wilson, B. P., Tross, J., . . . Trallero-Herrero, C. A. (2016). Atomic photoionization experiment by harmonic-generation spectroscopy. Physical Review A, 93(3), 5. doi:10.1103/PhysRevA.93.031403Measurements of the high-order-harmonic generation yield of the argon (Ar) atom driven by a strong elliptically polarized laser field are shown to completely determine the field-free differential photoionization cross section of Ar, i.e., the energy dependence of both the angle-integrated photoionization cross section and the angular distribution asymmetry parameter

Justice Through a Multispecies Lens

The bushfires in Australia during the Summer of 2019–2020, in the midst of which we were writing this exchange, violently heightened the urgency of the task of rethinking justice through a multispecies lens for all of the authors in this exchange, and no doubt many of its readers. As I finish this introduction, still in the middle of the Australian summer, more than 10 million hectares (100,000 km2 or 24.7 million acres) of bushland have been burned and over a billion individual animals killed. This says nothing of the others who will die because their habitat and the relationships on which they depend no longer exist. People all around the world are mourning these deaths and the destruction of unique ecosystems. As humans on this planet, and specifically as political theorists facing the prospect that such devastating events will only become more frequent, the question before us is whether we can rethink what it means to be in ethical relationships with beings other than humans and what justice requires, in ways that mark these deaths as absolute wrongs that obligate us to act, and not simply as unfortunate tragedies that leave us bereft

Characterizing the effects of the alkyl chain length of linear organic carbonates on lithium ion electrolyte structure and dynamics: A solvent perspective

© The Electrochemical Society. Lithium ion batteries have become the workhorse of the portable energy storage industry, yet there remains a strong need to improve their safety and efficiency. While many studies have focused on improving the electrodes or optimizing the electrolyte composition, few studies have focused on characterizing the electrolytes at the molecular level. In this work, we have utilized both steady-state and time-dependent infrared spectroscopies to characterize the structure and dynamics of the free carbonates both in neat solvents and within lithium-ion electrolytes. Time-resolved studies reveal similar dynamics of the bulk carbonates; however, a slowdown of the bulk carbonate dynamics occurs upon the addition of lithium salt. Thus, our studies reveal that the free carbonate molecules become significantly more ordered upon the addition of a lithium salt, which reveals further insight into the molecular-level structure of these electrolytes

Molecular motions, structure, and composition of carbonates in the solvation shell of the lithium ion, via infrared spectroscopies

© The Electrochemical Society. Structure property relations of lithium ion battery electrolytes have not been derived because fundamental questions about the lithium ion solvation shell structure and composition remain unanswered. We present a study of lithium hexafluorophosphate in pure carbonate solvents, of cyclic and linear structure, at commercial battery concentrations. Using a combination of infrared spectroscopies we have studied the solvation dynamics of the lithium ion in linear and cyclic carbonate solvents. Infrared experiments show the carbonyl stretch of the cyclic carbonate is broader than that of its linear analogue. In addition, the FFCF dynamics derived from the peak shift photon echo reveal that cyclic carbonates have much slower dynamics than linear carbonates. The contrasting differences observed in the organization, motions and composition of the lithium ion solvation shell for the cyclic and the linear carbonates can be explained with the insertion of a second solvation shell in the case of cyclic carbonates

A comparison of the solvation structure and dynamics of the lithium ion in linear organic carbonates with different alkyl chain lengths

© the Owner Societies 2017. The structure and dynamics of electrolytes composed of lithium hexafluorophosphate (LiPF6) in dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate were investigated using a combination of linear and two-dimensional infrared spectroscopies. The solutions studied here have a LiPF6 concentration of X(LiPF6) = 0.09, which is typically found in commercial lithium ion batteries. This study focuses on comparing the differences in the solvation shell structure and dynamics produced by linear organic carbonates of different alkyl chain lengths. The IR experiments show that either linear carbonate forms a tetrahedral solvation shell (coordination number of 4) around the lithium ion irrespective of whether the solvation shell has anions in close proximity to the carbonates. Moreover, analysis of the absorption cross sections via FTIR and DFT computations reveals a distortion in the angle formed by Li+-O=C which decreases from the expected 180° when the alkyl chains of the carbonate are lengthened. In addition, our findings also reveal that, likely due to its asymmetric structure, ethyl methyl carbonate has a significantly more distorted tetrahedral lithium ion solvation shell than either of the other two investigated carbonates. IR photon echo studies further demonstrate that the motions of the solvation shell have a time scale of a few picoseconds for all three linear carbonates. Interestingly, a slowdown of the in place-motions of the first solvation shell is observed when the carbonate has a longer alkyl chain length irrespective of the symmetry. In addition, vibrational energy transfer with a time scale of tens of picoseconds is observed between strongly coupled modes arising from the solvation shell structure of the Li+ which corroborates the modeling of these solvation shells in terms of highly coupled vibrational states. Results of this study provide new insights into the molecular structure and dynamics of the lithium ion electrolyte components as a function of solvent structure

Atomic Photoionization Experiment By Harmonic-Generation Spectroscopy

Measurements of the high-order-harmonic generation yield of the argon (Ar) atom driven by a strong elliptically polarized laser field are shown to completely determine the field-free differential photoionization cross section of Ar, i.e., the energy dependence of both the angle-integrated photoionization cross section and the angular distribution asymmetry parameter