Magnetic ground state and spin fluctuations in MnGe chiral magnet as studied by Muon Spin Rotation

TL;DR

This study uses muon spin resonance to investigate the magnetic ground state and spin fluctuations in MnGe, revealing complex helical order and fluctuating chiral phases with temperature-dependent dynamics.

Contribution

It provides detailed experimental insights into the magnetic phases of MnGe, including the characterization of helical order and spin fluctuations using muon spin resonance, and compares these findings with MnSi.

Findings

Double period oscillations indicate helical magnetic order.

Coexistence of rapid and slow spin fluctuations below T_N.

Temperature-dependent transition to inhomogeneous fluctuating chiral phase.

Abstract

We 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.