Helical magnetic order in EuAuSb

EuAuSb is a Dirac semimetal, one of a series of Eu compounds that share the hexagonal Ni₂In structure [1], where Eu layers alternate with mixed layers of Au and Sb. We studied the ordering of the large Eu²⁺ moments below the Néel temperature of 3.6 K by neutron diffraction as a function of in-plane magnetic field. Despite the large neutron absorption cross section of Eu, we were able to measure diffraction along (00L). The results are consistent with ferromagnetic alignment of Eu moments within each layer, with the spin direction rotating in a helical fashion by ~ 120^○ from one layer to the next. At low field, the helical order is slightly incommensurate but switches to commensurate in a field of 1 T and above. The ferromagnetic polarization gradually grows with field and the helical diffraction signal is lost when the field reaches 3 T. The magnetic phase diagram shows fascinating correlations with the striking magnetoresistance that has been measured.



1. C. Tomuschat and H.-U. Schuster, Z. Naturforsch. 36b, 1193 (1981).