Emergent Antiferromagnetism out of the "Hidden-Order" State in URu2Si2: High Magnetic Field Nuclear Magnetic Resonance to 40 T.

Very high field 29Si-NMR measurements using a fully 29Si-enriched URu2Si2 single crystal were carried out in order to microscopically investigate the "hidden order" (HO) state and adjacent magnetic phases in the high field limit. At the lowest measured temperature of 0.4 K, a clear anomaly reflecting a Fermi surface instability near 22 T inside the HO state is detected by the 29Si shift, 29Kc. Moreover, a strong enhancement of 29Kc develops near a critical field Hc≃35.6 T, and the 29Si-NMR signal disappears suddenly at Hc, indicating the total suppression of the HO state. Nevertheless, a weak and shifted 29Si-NMR signal reappears for fields higher than Hc at 4.2 K, providing evidence for a magnetic structure within the magnetic phase caused by the Ising-type anisotropy of the uranium ordered moments. [ABSTRACT FROM AUTHOR]