Phase diagram of CeRuPO under pressure investigated by 31P-NMR: Comparison between CeRuPO under pressure and the Ce(Ru1-xFex)PO system

We have performed P-31-NMR measurements on single-crystalline CeRuPO under pressure in order to understand the variation in magnetic character against pressure. The nuclear magnetic resonance (NMR) spectra for H perpendicular to c and H parallel to c at 2.15 GPa split below the ordered temperature, which is microscopic evidence of the change in the magnetic ground state from the ferromagnetic state at ambient pressure to the antiferromagnetic (AFM) state under pressure. The analysis of NMR spectra suggests that the magnetic structure in the AFM state is the stripe-type AFM state with the AFM moment m(AFM) perpendicular to c axis, and it changes with a magnetic field perpendicular to the c axis. In addition, the dimensionality of magnetic correlations in the spin and k space is estimated. We reveal that three-dimensional magnetic correlations in CeRuPO are robust against pressure, which is quite different from the suppression of the magnetic correlations along the c axis by Fe substitution in Ce(Ru1-xFex)PO.