Itinerant and local moment magnetism have substantively different origins, and require distinct theoretical treatment. A unified theory of magnetism has long been sought after, and remains elusive, mainly due to the limited number of known itinerant magnetic systems. In the case of the two such examples discovered several decades ago, the itinerant ferromagnets ZrZn2 and Sc3In, the understanding of their magnetic ground states draws on the existence of delocalized 3d electrons subject to strong spin fluctuations. Similarly, in Cr, an elemental itinerant antiferromagnet (IAFM) with a spin density wave (SDW) ground state, its 3d character has been deemed crucial to it being magnetic. In this talk I will present the properties of the recently-discovered IAFM compound with no magnetic constituents, Ti3Cu4. Antiferromagnetic order occurs below a Neel temperature TN ≈ 11 K, about an order of magnitude smaller than in Cr, rendering the spin fluctuations in Ti3Cu4 more important at low temperatures. This compound is only the second known IAFM with no magnetic elements, after TiAu. Small magnetic fields (Hc ~ 5 T) drive the magnetic order in Ti3Cu4 to 0 continuously, revealing the first field-induced quantum critical point in an itinerant magnet. This new IAFM challenges the currently limited understanding of weak itinerant antiferromagnetism, while providing long sought-after insights into the effects of spin fluctuations in itinerant electron systems.
