Anisotropic spin-fluctuations in SmCoPO revealed by 31^P NMR measurement

Abstract: 31^P NMR spectral features in polycrystalline SmCoPO reveal an axially symmetric local magnetic field. At low temperature, the anisotropy of the internal magnetic field increases rapidly, with K_ab increasing faster than that of K_c. The dominant contribution to this anisotropy arises from Sm-4f electron contribution over that of Co-3d. The intrinsic width 2*(Beta) deviates from linearity with respect to bulk susceptibility below 170 K due to the enhancement of (1/T_2)dynamic, which along with the continuous increase of anisotropy in the internal magnetic field is responsible for the wipe out effect of the NMR signal, well above T_C. 1/T_1 shows large anisotropy confirming a significant contribution of Sm-4f electron spin fluctuations to 1/T_1, arising from indirect RKKY type exchange interaction indicating a non-negligible hybridization between Sm-4f orbitals and the conduction band, over the itinerant character of the Co-3d spins. This anisotropy in originates from the orientation dependence of chi"(q,omega). The 3d-spin fluctuations in the ab plane is 2D FM in nature, while along the c-axis, a signature of a weak 2D AFM spin fluctuations superimposed on weak FM spin-fluctuations even in a field of 7 T and far above T_N is observed. The enhancement of this AFM fluctuations of the Co-3d spins along c-axis, at further low temperature is responsible to drive the system to an AFM ordered state.