Abstract
We report a comprehensive small-Angle neutron scattering (SANS) study of magnetic correlations in Mn1-xFexSi at zero magnetic field. To delineate changes of magnetocrystalline anisotropies (MCAs) from effects due to defects and disorder, we recorded complementary susceptibility and high-resolution specific heat data and investigated selected compositions of Mn1-xCoxSi. For all systems studied, the helimagnetic transition temperature and magnetic phase diagrams evolve monotonically with composition consistent with literature. The SANS intensity patterns of the spontaneous magnetic order recorded under zero-field cooling, which were systematically tracked over forty angular positions, display strong changes of the directions of the intensity maxima and smeared out intensity distributions as a function of composition. We show that cubic MCAs account for the complex evolution of the SANS patterns, where for increasing x the character of the MCAs shifts from terms that are fourth order to terms that are sixth order in spin-orbit coupling. The magnetic field dependence of the susceptibility and SANS establishes that the helix reorientation as a function of magnetic field for Fe-or Co-doped MnSi is dominated by pinning due to defects and disorder. The presence of well-defined thermodynamic anomalies of the specific heat at the phase boundaries of the skyrmion lattice phase in the doped samples and properties observed in Mn1-xCoxSi establishes that the pinning due to defects and disorder remains, however, weak and comparable to the field scale of the helix reorientation. The observation that MCAs, which are sixth order in spin-orbit coupling, play an important role for the spontaneous order in Mn1-xFexSi and Mn1-xCoxSi offers a fresh perspective for a wide range of topics in cubic chiral magnets such as the generic magnetic phase diagram, the morphology of topological spin textures, the paramagnetic-To-helical transition, and quantum phase transitions.
| Original language | English |
|---|---|
| Article number | 104406 |
| Journal | Physical Review B |
| Volume | 101 |
| Issue number | 10 |
| DOIs | |
| State | Published - Mar 1 2020 |
Funding
We wish to thank P. B\u00F6ni, C. Franz, M. Halder, S. Mayr, F. Rucker, and C. Schnarr for fruitful discussions and assistance with the experiments. This work has been funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) through TRR80 (From Electronic Correlations to Functionality, Project No. 107745057, Projects E1 and F7), FOR960 (Project No. 48554140), SPP2137 (Skyrmionics, Project No. 403191981, Projects 403030645 and 403191981), and the excellence cluster MCQST under Germany's Excellence Strategy EXC-2111 (Project No. 390814868). Financial support by the Bundesministerium f\u00FCr Bildung und Forschung (BMBF) through Project No. 05K16WO6 as well as by the European Research Council (ERC) through Advanced Grants No. 291079 (TOPFIT) and No. 788031 (ExQuiSid) is gratefully acknowledged. M.G. is supported by DFG SFB1143 (Correlated Magnetism: From Frustration to Topology, Project No. 247310070, Project A07), DFG Grant No. 1072/5-1, and DFG Grant No. 1072/6-1. J.K., T.A., F.H., and A.C. acknowledge financial support through the TUM Graduate School.