  The high brilliance of the modern synchrotron radiation sources facilitates
experiments with high energy x-rays. In this Letter we report on Nuclear
Resonance Scattering at the 73 keV nuclear level in 193Ir. The transitions
between the hyperfine split levels show an exceptionally large E2/M1
multi-polarity mixing ratio combined with an increased sensitivity to certain
changes in the hyperfine field direction compared to non-mixing transitions.
The method opens a new way for probing local magnetic and electronic properties
of correlated materials containing iridium and provides novel insights into
their anisotropic magnetism. In particular, unexpected out-of-plane components
of magnetic hyperfine fields and non-zero electric field gradients in Sr2IrO4
have been detected and attributed to the presence of strong spin-orbit
interaction. Due to the high, 62% natural abundance of the 193Ir isotope, no
isotopic enrichment of the samples is required, qualifying the method for a
broad range of applications.
