Paper detail

Local electromagnetic properties of magnetic pnictides: A comparative study probed by NMR measurement

75As and 31P NMR studies are performed in PrCoAsO and NdCoPO respectively. The Knight shift data in PrCoAsO indicate the presence of an antiferromagnetic interaction between the 4f moments along the c axis in the ferromagnetic state of Co 3d moments. We propose a possible spin structure in this system. The 75As quadrupolar coupling constant, $ν_Q$ increases continuously with the decrease of temperature and is found to vary linearly with the intrinsic spin susceptibility, Kiso. This indicates a possibility of the presence of a coupling between charge density and spin density fluctuations. Further, 31P NMR Knight shift and spin lattice relaxation rate (1/T1) in the paramagnetic state of NdCoPO indicate that the differences between LaCoPO and NdCoPO with SmCoPO are due to the decrement of inter layer separation and not due to the moments of 4f electrons. Nuclear spin lattice relaxation time (T1) in NdCoPO shows weak anisotropy at 300 K. Using self consistent renormalization (SCR)theory of itinerant ferromagnet, it is shown that in the ab plane, the spin fluctuations are three dimensional ferromagnetic in nature. From SCR theory the important spin fluctuation parameters ($T_0$, $T_A$, $\bar{F}_1$) are evaluated. The similarities and dissimilarities of the NMR results in As and P based systems, with different rare earths have also been discussed.