Chiral Magnetism in an Itinerant Helical Magnet, MnSi - An Extended 29Si NMR Study -

TL;DR

This study uses extended 29Si NMR to investigate the microscopic magnetism in MnSi across different magnetic phases, revealing field-induced electronic state changes and supporting the SCR theory for itinerant ferromagnets.

Contribution

It provides detailed NMR insights into the magnetic phases of MnSi, including a first-order transition at the critical field, extending understanding of itinerant helimagnetism.

Findings

Temperature dependence of staggered moment aligns with SCR theory.

Resonance frequency follows a vector sum of hyperfine and macroscopic fields.

Discontinuous jump at critical field indicates a first-order phase transition.

Abstract

The microscopic magnetism in the helical, the conical and the ferro-magnetically polarized phases in an itinerant helical magnet, MnSi, has been studied by an extended 29Si NMR at zero field and under external magnetic fields. The temperature dependence of staggered moment, M_Q(T), determined by the 29Si NMR frequency, nu(T), and nuclear relaxation rate, 1/T_1(T) is in general accord with the SCR theory for weak itinerant ferromagnetic metals and its extension. The external field dependence of resonance frequency, nu(H), follows a vector sum of the contributions from atomic hyperfine and macroscopic fields with a field induced moment characteristic to the itinerant magnets. A discontinuous jump of the resonance frequency at the critical field, H_c, between the conical and the polarized phases has also been found that suggests a first order like change of the electronic states at H_c.