Magnetic ground state and spin fluctuations in MnGe chiral magnet as studied by muon spin rotation

Abstract

International audienceWe have studied by muon spin resonance (mu SR) the helical ground state and fluctuating chiral phase recently observed in the MnGe chiral magnet. At low temperature, the muon polarization shows double-period oscillations at short-time scales. Their analysis, akin to that recently developed for MnSi [A. Amato et al., Phys. Rev. B 89, 184425 (2014)], provides an estimation of the field distribution induced by the Mn helical order at the muon site. The refined muon position agrees nicely with ab initio calculations. With increasing temperature, an inhomogeneous fluctuating chiral phase sets in, characterized by two well-separated frequency ranges which coexist in the sample. Rapid and slow fluctuations, respectively, associated with short-range and long-range ordered helices, coexist in a large temperature range below T-N = 170 K. We discuss the results with respect to MnSi, taking the short helical period, metastable quenched state, and peculiar band structure of MnGe into account

Magnetic structure of the MnGe helimagnet and representation analysis

“…8 and 24). This is in accord with the ab initio computations which predict a value for x µ slightly larger in MnGe than in MnSi, namely 0.554 vs 0.542 [15,25].…”

“…2) and at variance to the MnSi case. No such small coherence length was signaled in the MnGe neutron diffraction work [5], but the strong damping of the µSR oscillations was associated with the disorder inherent to the magnetic structure [15]. Note that with our model, the parameter ξ accounts in fact for the effects of both magnetic disorder and spin-spin relaxation.…”

Reverse Monte Carlo Algorithm and Maximum Entropy Principle for the Analysis of Positive Muon Spin Rotation and Relaxation Spectra

“…We have checked that A FT (B) = 0 around 2.0 T. On the other hand, as expected D ocs (B) is always positive and vanishes above ≈ 1300 mT. We attribute the offset of A FT (B) to the absence of data for time shorter than ≈ 3 ns with an asymmetry approaching the initial value of 0.245 expected for the spectrometer [28]. In curve-fitting and with the ME-RMC algorithm the initial asymmetry of the oscillating part of the asymmetry is fixed to a value determined by the spectrometer characteristics.…”

High-pressure magnetic state of MnP probed by means of muon-spin rotation

“…wide-gap semiconductors, insulating systems or cuprate and iron-based high-T c superconductors. [20][21][22][23][24][25] There are four equivalent minima in the unit cell corresponding to the 4c [(x, 1/4, z), x µ = 0.103, z µ = 0.921] Wyckoff position (see the Supplementary part). The calculations were started from the known FM and Hel−c magnetic structures at ambient pressure (see Refs.…”