Universality of the helimagnetic transition in cubic chiral magnets: Small angle neutron scattering and neutron spin echo spectroscopy studies of FeCoSi
Lars J. Bannenberg (TU Delft - RST/Neutron and Positron Methods in Materials)
K. Kakurai (RIKEN Center for Emergent Matter Science (CEMS), Neutron Science and Technology Center, CROSS Tokai)
P Falus (Institut Laue Langevin)
E. Lelievre-Berna (Institut Laue Langevin)
RM Dalgliesh (ISIS, Rutherford Appleton Laboratory)
C. D. Dewhurst (Institut Laue Langevin)
F. Qian (TU Delft - RST/Neutron and Positron Methods in Materials)
Y. Onose (University of Tokyo)
Y. Endoh (RIKEN Center for Emergent Matter Science (CEMS))
Y. Tokura (University of Tokyo, RIKEN Center for Emergent Matter Science (CEMS))
C. Pappas (TU Delft - RST/Neutron and Positron Methods in Materials)
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Abstract
We present a comprehensive Small Angle Neutron Scattering (SANS) and Neutron Spin Echo Spectroscopy (NSE) study of the structural and dynamical aspects of the helimagnetic transition in Fe1-xCoxSi with x = 0.30. In contrast to the sharp transition observed in the archetype chiral magnet MnSi, the transition in Fe1-xCoxSi is gradual and long-range helimagnetic ordering coexists with short-range correlations over a wide temperature range. The dynamics are more complex than in MnSi and involve long relaxation times with a stretched exponential relaxation which persists even under magnetic field. These results in conjunction with an analysis of the hierarchy of the relevant length scales show that the helimagnetic transition in Fe1-xCoxSi differs substantially from the transition in MnSi and question the validity of a universal approach to the helimagnetic transition in chiral magnets.