Agradecimentos: We thank H. Ikeda, K. Kuwahara, D. Aoki, and K. Sugiyama for valuable discussions. Work in Japan was supported by the Reimei Research Program of JAEA. Work at NHMFL was performed under the auspices of the NSF through the Cooperative Agreement No. DMR-0654118 and the State of Florida. R. R. U. also acknowledges FAPESP (No. 2012/05903-6). Work at LANL was performed under the auspices of the U.S. DOE, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering Ver menos

Abstract: Very high field Si-29-NMR measurements using a fully Si-29-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 Si-29 shift, K-29(c) Moreover, a strong enhancement of K-29(c) develops near a critical field H-c similar or equal to 35.6 T, and the Si-29-NMR signal disappears suddenly at H-c, indicating the total suppression of the HO state. Nevertheless, a weak and shifted Si-29-NMR signal reappears for fields higher than H-c 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 Ver menos