Direct Evidence of Magnetoelastic Coupling in Ni$_{3}$V$_{2}$O$_{8}$.*

We investigate the infrared active phonons of the Kagome staircase compound Ni$_{3}$V$_{2}$O$_{8}$ as a function of temperature to elucidate changes in magnetoelastic coupling through the cascade of low-temperature magnetic transitions. A detailed analysis of the $a$- and $c$- polarized vibrational mode trends demonstrates that: i) the approach to the cascade of magnetic transitions is driven by the high frequency stretching modes and the highest frequency bending mode along $a$; ii) the paramagnetic to high-temperature incommensurate phase transition is driven by low frequency $c$-polarized modes; and iii) the high-temperature to low-temperature incommensurate phase transition is driven by all $a$-polarized modes plus the NiO$_{6}$ stretching mode along $c$. Work is in progress to elucidate the trends along $b$. Overall, we find that the phonons are sensitive to the magnetic state, indicating that the lattice is flexible, coupling strongly to the spin system in this multiferroic material.