We present a comprehensive investigation of the evolution of helimagnetic correlations in Mn1−xFexSi with increasing doping. By combining polarized neutron scattering and high resolution neutron spin echo spectroscopy we investigate three samples with x = 0.09, 0.11, and 0.14, i.e., with compositions on both sides of the concentration x∗∼0.11 where the helimagnetic Bragg peaks disappear and between x∗ and the quantum critical concentration xC∼0.17, where TC vanishes. We find that the abrupt disappearance of the long range helical periodicity at x∗ does not affect the precursor fluctuating correlations. These build up with decreasing temperature in a similar way as for the parent compound MnSi. Also the dynamics bears strong similarities to MnSi. The analysis of our results indicates that frustration, possibly due to achiral Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions, increases with increasing Fe doping. We argue that this effect explains both the expansion of the precursor phase with increasing x and the abrupt disappearance of long range helimagnetic periodicity at x∗.@en

According to standard theory the magnetoresistance magnitude in ferromagnetic manganites crucially depends on the electron-phonon coupling strength. We showed that in La0.7Sr0.3MnO3 the phonon renormalization is strong, despite its relatively small magnetoresistance. Here, we report results of a similar inelastic neutron-scattering investigation of a closely related compound, La0.8Sr0.2MnO3, where the magnetoresistance is enhanced. We find similar phonon renormalization and dynamic CE-type polaron correlations as in La0.7Sr0.3MnO3. However, quantitative comparison of the results for the two samples shows that only polaron lifetime is well correlated with the strength of the colossal magnetoresistance.

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We present a comprehensive small-angle neutron scattering study of the doping dependence of the helimagnetic correlations in Mn1−xFexSi. The long-range helimagnetic order in Mn1−xFexSi is suppressed with increasing Fe content and disappears for x>x∗≈0.11, i.e., well before xC≈0.17 where the transition temperature vanishes. For x>x∗, only finite isotropic helimagnetic correlations persist which bear similarities with the magnetic correlations found in the precursor phase of MnSi. Magnetic fields gradually suppress and partly align these short-ranged helimagnetic correlations along their direction through a complex magnetization process@en

The family of rare-earth (R) tritellurides RTe3 features charge-density-wave (CDW) order related to strongly momentum-dependent electron-phonon coupling. Similar to other CDW compounds, superconductivity is observed when the CDW order is suppressed via hydrostatic pressure [J. J. Hamlin, Phys. Rev. Lett. 102, 177002 (2009)10.1103/PhysRevLett.102.177002]. What sets the heavier members of the RTe3 series apart is the observation of a second CDW transition at lower temperatures having an in-plane ordering wave vector qCDW,2 [100] of almost the same magnitude but orthogonal to the ordering wave vector qCDW,1 [001] observed at higher temperatures [N. Ru, Phys. Rev. B 77, 035114 (2008)10.1103/PhysRevB.77.035114]. Here, we report an inelastic x-ray scattering investigation of the lattice dynamics of DyTe3 In particular, we show that there are several phonon modes along both in-plane directions, which respond to the onset of the CDW transition at TCDW,1=308K. Surprisingly, these soft modes close to qCDW,2=(0.68,0,0) show strong softening near TCDW,1 but do not exhibit any response to the lower-temperature transition at TCDW,2=68K. Our results indicate that the low-temperature CDW order is not just the 90° rotated analogue of the one appearing at high temperatures.

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We present a comprehensive and systematic magnetization and ac susceptibility study of Mn1-xFexSi over an extensive range of ten Fe concentrations between x=0 and x=0.32. With increasing Fe substitution, the critical temperature decreases but the magnetic phase diagrams remain qualitatively unaltered for x≤x∗≈0.11 with clear boundaries between the helical, conical, and skyrmion lattice phase as well as an enhanced precursor phase. A notably different behavior sets in for x=0.11,0.13, and 0.14, where certain characteristics of helimagnetic correlations persist, but without clear phase boundaries. Although a qualitative change already sets in at x∗, the transition temperature and spontaneous magnetization vanish only at xc=0.17 where also the average magnetic interactions change sign. Although the Curie-Weiss temperature reaches -12 K for x=0.32, no signature of long-range magnetic order is found down to the lowest temperature, indicating a possible significant role for quantum fluctuations in these systems. © 2018 American Physical Society.@en