Helimagnetism in gallium substituted LuMn6Ge6 studied by nuclear magnetic resonance

Abstract

Zero-field nuclear magnetic resonance (NMR) of all NMR isotopes (175Lu, 55Mn, 73Ge, 69,71Ga) in LuMn6Ge6-xGax, 0 ≤ x ≤ 1, is used to monitor the variation of the hyperfine interaction with the sequence of antiferromagnetic - helimagnetic - ferromagnetic arrangement of the manganese moments of subsequent Kagome net planes achieved by variation of the gallium content x. According to the 55Mn-NMR results, the local Mn moment varies by less than ±5% in this series. 175Lu-NMR proves canting of the antiferromagnetic sublattices in LuMn6Ge6. The anisotropy of the Ge magnetic hyperfine interaction decreases with increasing separation from the hexagonal Lu plane, whereas the absolute value of its isotropic part is only qualitatively correlated with the average separation of the six nearest Mn neighbours. Due to the anisotropic magnetic and electric hyperfine interaction at Ge and Ga sites, the non-collinear magnetic structures are clearly reflected by the NMR spectra, which are described quantitatively in this contribution. The preferred Mn moment direction rotates away from the c direction with x. The conduction or bonding electron spin polarization at the Ga nuclei is increased by 35–80% compared to the Ge nuclei. We argue that this is related with the variation of the magnetic order with the Ga content.