Distinct itinerant spin-density waves and local-moment antiferromagnetism in an intermetallic ErPd(2)Si(2) single crystal

Identifying the nature of magnetism, itinerant or localized, remains a major challenge in condensed-matter science. Purely localized moments appear only in magnetic insulators, whereas itinerant moments more or less co-exist with localized moments in metallic compounds such as the doped-cuprate or the iron-based superconductors, hampering a thorough understanding of the role of magnetism in phenomena like superconductivity or magnetoresistance. Here we distinguish two antiferromagnetic modulations with respective propagation wave vectors at Q(±) = (H ± 0.557(1), 0, L ± 0.150(1)) and Q(C) = (H ± 0.564(1), 0, L), where (H, L) are allowed Miller indices, in an ErPd(2)Si(2) single crystal by neutron scattering and establish their respective temperature- and field-dependent phase diagrams. The modulations can co-exist but also compete depending on temperature or applied field strength. They couple differently with the underlying lattice albeit with associated moments in a common direction. The Q(±) modulation may be attributed to localized 4f moments while the Q(C) correlates well with itinerant conduction bands, supported by our transport studies. Hence, ErPd(2)Si(2) represents a new model compound that displays clearly-separated itinerant and localized moments, substantiating early theoretical predictions and providing a unique platform allowing the study of itinerant electron behavior in a localized antiferromagnetic matrix.