  Magnetic excitations and the spin Hamiltonian of the spin-1 J1-J1-J2 trimer
chain compound CaNi3P4O14 have been investigated by inelastic neutron
scattering. Experimental data reveal gapped dispersive spin wave excitations in
the 3D long-range ordered magnetic state (TC = 16 K), and gapless magnetic
excitations above the TC. Simulated magnetic excitations, by using the linear
spin wave theory, for a model of coupled trimer spin-chains provide a good
description of the observed experimental data. The analysis reveals both
ferromagnetic J1 and J2 interactions within the chains, and an
antiferromagnetic interchain interaction J3 between chains. The strengths of
the J1 and J2 are found to be closer (J2/J1 ~ 0.81), and J3 is determined to be
weaker (J3/ J1 ~ 0.69), which is consistent with the spin chain type crystal
structure. Presence of a weak single-ion-anisotropy (D/J=0.19) is also
revealed. The strengths and signs of exchange interactions explain why the 1/3
magnetization is absent in the studied spin-1 compound CaNi3P4O14 in contrast
to its S= 5/2 counterpart Mn based isostructural compound. The signs of the
exchange interactions are in agreement with that obtained from the reported DFT
calculations, whereas, their strengths are found to be significantly different.
The relatively strong value of the J3 in CaNi3P4O14 gives a conventional 3D
type magnetic ordering below the TC, however, retains its 1D character above
the TC. The present experimental study also reveals a sharp change of
single-ion anisotropy across the TC indicating that the stability of the 3D
magnetic ordering in CaNi3P4O14 is ascribed to the local magnetic anisotropy in
addition to interchain interactions. The present study divulges the importance
of full knowledge of the exchange interactions in trimer spin chain compounds
to understand their exotic magnetic properties, such as 1/3 magnetization
plateau.
