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

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 29 Si NMR at zero field and under external magnetic fields. The temperature dependence of staggered moment, MQ(T), determined by the 29 Si NMR frequency, (T), and nuclear relaxation rate, 1/T1(T) is in general accord with the SCR theory for weak itinerant ferromagnetic metals and its extension. The external field dependence of resonance frequency, (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, Hc, between the conical and the polarized phases has also been found that suggests a first order like change of the electronic states at Hc.

Zero-field 29Si nuclear magnetic resonance signature of helimagnons in MnSi

“…Temperature T (K) ν of the 29 Si resonance. This quantity is a good and accurate measure of the temperature dependence of the staggered magnetic moment [13]. From Fig.…”

“…Here we will consider the data from Ref. [13] for which a temperature dependence is available. This is 29 Si NMR, where the spin of the resonant nucleus is 1/2.…”

“…Published data [13] of the temperature dependence of the spin-lattice relaxation rate and of the zero-field NMR frequency at low temperature have been successfully interpreted in the helimagnon framework. The form of the dispersion relation predicted by theory is verified.…”

“…[12]. Here we consider a recent NMR study of MnSi in its magnetically ordered phase [13]. We restrict ourselves to data recorded in zero applied field [14,15]: the MnSi magnetic structure is then purely helical and the dispersion relation is not affected by any additional term.…”

Evolution of helimagnetic correlations when approaching the quantum critical point of Mn1−xFexSi

“…The physics of the chiral magnet MnSi touches onto several fundamental questions in condensed-matter physics, from the stabilisation of exotic states like chiral skyrmions [1] to the interplay between localised and itinerant magnetism [2][3][4][5][6][7][8] as well as to non-Fermi liquid behaviour [9][10][11][12][13][14] and quantum fluctuations [15][16][17][18][19][20][21][22][23]. Under pressure a non-Fermi liquid behaviour sets-in without quantum criticality [11,15,24,25].…”