Paramagnetic spin fluctuations in the weak itinerant-electron ferromagnet MnSi

Abstract

Paramagnetic spin fluctuations in the weak itinerant-electron ferromagnet MnSi have been measured by using both unpolarized and polarized neutron scattering, and the scattering intensity was put on an absolute value by the simultaneous measurements of phonon cross sections. The magnetic excitation spectra over the whole Brillouin zone, for a wide energy range from 0 to 20 meV (ħω/${\mathrm{kT}}_c$=7.9) and up to temperatures (T/$T_c$=10) well above $T_c$, follow closely the Moriya-Kawabata self-consistent-renormalization theory for the weak itinerant-electron ferromagnet. Based on these experimental results, the origin of the increase in the amplitude of the local magnetic moment 〈$M_L^2$〉 above $T_c$ is attributed to the thermal excitations of the high-energy spin fluctuations in the Stoner continuum.