Excitation spectrum in a spin-1 chain with alternating easy-axis direction

We plan to study a spin-1 antiferromagnet Ni(pym)(NO3)2(D2O)2, where the Ni(II) ions are connected in a staggered chain structure. Previous studies of similar spin-1/2 Cu(II) systems revealed a host of exotic excitations that map on the soliton and breather modes of the sine-Gordon model of quantum-field-theory. Spin-1 chains, however, are known to differ fundamentally from their spin-1/2 counterparts, and the structure of these materials suggests the presence of an unusual, alternating single-ion anisotropy. Recently, we studied a chiral spin-1 chain material [Ni(pym)(H2O)4]SO4 using inelastic neutron scattering (INS) on the LET instrument. Below the long-range ordering temperature, we find an information-rich excitation spectrum, which arises from the four-fold periodic alternation of the local easy axis. Similarly, in the staggered chain, we expect that the competition between the alternating anisotropy and antiferromagnetic will give rise to a unique excitation spectrum. However, preliminary calculations suggest a behaviour that is different to its chiral cousin. Understanding these differences will help us get to the bottom of the complex magnetic properties displayed by this new class of quantum spin chains. Therefore, we propose to use zero-field inelastic neutron scattering, below magnetic ordering temperatures Tc = 2.3 K, at LET to quantify the energy scales governing the magnetic properties and map the excitation spectra.