Small-angle neutron scattering study of mesoscale magnetic disordering and skyrmion phase suppression in the frustrated chiral magnet Co6.75Zn6.75Mn6.5

Jonathan S White; Kosuke Karube; Victor Ukleev; P M Derlet; R Cubitt; C D Dewhurst; A R Wildes; X Z Yu; H M Rønnow; Yoshinori Tokura; Yasujiro Taguchi

doi:10.1107/S1600576722007403

Small-angle neutron scattering study of mesoscale magnetic disordering and skyrmion phase suppression in the frustrated chiral magnet Co_6.75Zn_6.75Mn_6.5

J Appl Crystallogr. 2022 Sep 14;55(Pt 5):1219-1231. doi: 10.1107/S1600576722007403. eCollection 2022 Oct 1.

Authors

Jonathan S White¹, Kosuke Karube², Victor Ukleev¹, P M Derlet³, R Cubitt⁴, C D Dewhurst⁴, A R Wildes⁴, X Z Yu², H M Rønnow⁵, Yoshinori Tokura^{2

6

7}, Yasujiro Taguchi²

Affiliations

¹ Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institute, Villigen, CH-5232, Switzerland.
² Center for Emergent Matter Science (CEMS), RIKEN, Wako, 351-0198, Japan.
³ Condensed Matter Theory Group, Paul Scherrer Institute, Villigen, CH-5232, Switzerland.
⁴ Institut Laue-Langevin, 71 avenue des Martyrs, CS 20156, Grenoble, 38042 Cedex 9, France.
⁵ Laboratory for Quantum Magnetism (LQM), Institute of Physics, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, CH-1015, Switzerland.
⁶ Department of Applied Physics, University of Tokyo, Bunkyo-ku, 113-8656, Japan.
⁷ Tokyo College, University of Tokyo, Bunkyo-ku, 113-8656, Japan.

Abstract

Co-Zn-Mn chiral cubic magnets display versatile magnetic skyrmion phases, including equilibrium phases stable far above and far below room temperature, and the facile creation of robust far-from-equilibrium skyrmion states. In this system, compositional disorder and magnetic frustration are key ingredients that have profound effects on the chiral magnetism. Reported here are studies of the magnetism in Co_6.75Zn_6.75Mn_6.5 by magnetometry, small-angle neutron scattering (SANS), magnetic diffuse neutron scattering and Lorentz transmission electron microscopy (LTEM). While features in magnetometry and LTEM often give standard indications for skyrmion formation, they are not readily observed from the measurements on this system. Instead, skyrmion lattice correlations are only revealed by SANS, and they are found to form an orientationally disordered structure in a minority fraction of the sample. The majority fraction of the sample always displays orientationally disordered helical spin correlations, which undergo further disordering along the radial direction on cooling below the critical temperature (T _c ≃ 102 K). The near-complete suppression of the skyrmion phase, and the process of disordering on cooling, are attributed to competing magnetic interactions that dominate over the ferromagnetic interaction expected to favour chiral magnetism in this system. These competing interactions start to develop above T _c and become further enhanced towards low temperatures. The present observations of co-existing and disordered magnetic correlations over multiple length scales are not unique to Co_6.75Zn_6.75Mn_6.5 but are seemingly common to the family of Co-Zn-Mn compounds with finite Mn, and their accurate description presents a challenge for theoretical modelling. In addition, this study highlights a need for neutron instrumentation capable of the comprehensive measurement of magnetic correlations over expanded ranges of momentum transfer in such multiple-length-scale magnets.

Keywords: chiral magnets; diffuse scattering; frustration; magnetic disorder; skyrmions; small-angle neutron scattering.

Grants and funding

This work was supported by the Swiss National Science Foundation (SNF) (Sinergia project CRSII5_171003 NanoSkyrmionics and project No. 200021_188707 to Jonathan S. White and Victor Ukleev), by JSPS Grants-in-Aid for Scientific Research (grant No. 20K15164 to Kosuke Karube and Yasujiro Taguchi), and by JST CREST (grant Nos. JPMJCR20T1 and JPMJCR1874).