Spin trimers in Ca3Cu2Ni(PO4)4

The nature of spin trimer and 3d spin dynamics in Ca3Cu2Ni(PO4)(4) is studied using P-31 NMR measurements. The data are obtained by replacing one of the Cu ions by a Ni ion in the one dimensional spin trimer compound Ca3Cu3(PO4)(4). The NMR spectrum suggests the presence of two types of magnetically inequivalent phosphorous atoms, as in the parent compound. This reveals the presence of only one type of trimer, Cu2-Ni-Cu2, rather than of three types, Cu2-Cu1-Cu2, Cu2-Cu1-Ni and Ni-Cu1-Ni, as indicated by neutron scattering. Hence, the ground state of Ca3Cu2Ni(PO4)(4) appears to be a quintet. These results also explain the magnetic susceptibility behavior, which indicates no reduction in the net spin of the trimer in Ca3Cu2Ni(PO4)(4), as expected for J(Ni-Cu) = -0.85 meV compared to the value J(Cu-Cu) = -4.74 meV derived from neutron scattering. The spin lattice relaxation rate suggests that the three magnon mediated scattering process dominant in Ca3Cu2Ni(PO4)(4) is reduced in Ca3Cu2Ni(PO4)(4). (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4734011]