Monopole-limited nucleation of magnetism in Eu${}_2$Ir${}_2$O${}_7$

Abstract

We present an in-depth analysis of muon-spin spectroscopy measurements of Eu${}_2$Ir${}_2$O${}_7$ under the effect of the Eu${}_{1-x}$Bi${}_x$ isovalent and diamagnetic substitution as well as of external pressure. Our results evidence an anomalously slow increase of the magnetic volume fraction upon decreasing temperature only for stoichiometric Eu${}_2$Ir${}_2$O${}_7$, pointing towards highly unconventional properties of the magnetic phase developing therein. We argue that magnetism in Eu${}_2$Ir${}_2$O${}_7$ develops based on the nucleation of magnetic droplets at $T_N$, whose successive growth is limited by the need of a continuous generation of magnetic hedgehog monopoles.

9 pages, 4 figures