Low energy spin dynamics in trimer spin chain compound Ca3Cu2Ni(PO4)4: 31P NMR study

31P nuclear-magnetic-resonance (NMR) study in the trimer spin chain compound Ca3Cu2Ni(PO4)4 is performed in the presence of different external magnetic fields in the temperature range 4–300 K. The results suggest that the three magnon mediated scattering process which was the dominant contribution to 1/T1 in the pure compound Ca3Cu3(PO4)4, has negligible contribution in Ca3Cu2Ni(PO4)4, with the two magnon mediated Raman process being dominant. The linear variation of nuclear spin lattice relaxation rate 1/T1T   with the magnetic susceptibility χχ indicates that the Q   component of magnetic susceptibility χ(Q)χ(Q) is nearly proportional to χχ, where Q is the antiferromagnetic wave vector. A change in the slope of 1/T1T   with respect to χχ near 15 K suggests a change in the antiferromagnetic spin fluctuation spectrum. Below 15 K, the spin diffusion mechanism governs the 1/T1 process. This could be a signature of the development of short range magnetic correlation or due to the contribution arising from the paramagnetic impurity spins.