Probing strongly hybrid nuclear-electronic states in a model quantum   ferromagnet
  We present direct local-probe evidence for strongly hybridized nuclear-electronic spin states of an Ising ferromagnet LiHoF$_4$ in a transverse magnetic field. The nuclear-electronic states are addressed via a magnetic resonance in the GHz frequency range using coplanar resonators and a vector network analyzer. The magnetic resonance spectrum is successfully traced over the entire field-temperature phase diagram, which is remarkably well reproduced by mean-field calculations. Our method can be directly applied to a broad class of materials containing rare-earth ions for probing the substantially mixed nature of the nuclear and electronic moments. 
I. Kovacevic, P. Babkevich, M. Jeong, J. O. Piatek, G. Boero, and H.   M. R{\o}nnow
cond-mat.str-el quant-ph