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 anomalous correlation between the magnetic volume fraction and the order parameter 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.