Experimental evidence of a change of exchange anisotropy sign with temperature in Zn-substituted Cu2OSeO3

Moody, S.H.; Nielsen, P.; Wilson, M.N.; Venero, D. Alba; Štefančič, A.; Balakrishnan, G.; Hatton, P.D.

Abstract

We report small-angle neutron scattering from the conical state in a single crystal of Zn-substituted Cu 2 OSeO 3 . Using a 3D vector-field magnet to reorient the conical wave vector, our measurements show that the magnitude of the conical wave vector changes as a function of crystallographic direction. These changes are explained using the anisotropic exchange interaction (AEI) within the continuum model, whose magnitude in free-energy transitions from a maxima to a minima along the ⟨ 111 ⟩ and ⟨ 100 ⟩ crystallographic directions respectively. We further find that the AEI free-energy constant undergoes a change of sign from positive to negative with decreasing temperature. Unlike in the related compound FeGe, where similar behavior of the AEI induces a reorientation of the helical wave vector, we show that the zero field helical wave vector in ( Cu 0.98 Zn 0.02 ) 2 OSeO 3 remains along the ⟨ 100 ⟩ directions at all temperatures due to the competing fourth-order magnetocrystalline anisotropy becoming dominant at lower temperatures.

Citation

Moody, S., Nielsen, P., Wilson, M., Venero, D. A., Štefančič, A., Balakrishnan, G., & Hatton, P. (2021). Experimental evidence of a change of exchange anisotropy sign with temperature in Zn-substituted Cu2OSeO3. Physical Review Research, 3(4), Article 043149. https://doi.org/10.1103/physrevresearch.3.043149

• Journal Article Type: Article
• Acceptance Date: Oct 27, 2021
• Online Publication Date: Dec 1, 2021
• Publication Date: 2021
• Deposit Date: Jan 7, 2022
• Publicly Available Date: Jan 7, 2022
• Journal: Physical Review Research
• Publisher: American Physical Society
• Peer Reviewed: Peer Reviewed
• Volume: 3
• Issue: 4
• Article Number: 043149
• DOI: https://doi.org/10.1103/physrevresearch.3.043149