Unusual dimerization and magnetization plateaus in S = 1 skew chain Ni2V2O7 observed at 120 T

Abstract

Using ultrahigh magnetic field up to 120 T, a 1/2 magnetization plateau within $11.7--34.8$ T and a 3/4-like plateau within $55.6--87.0$ T have been observed in the $S$-1 skew chain antiferromagnet ${\mathrm{Ni}}_{2}{\mathrm{V}}_{2}{\mathrm{O}}_{7}$. By combining density functional theory calculations, exact diagonalization, and quantum Monte Carlo simulations, we find that the nearest-neighbor interchain interaction (${J}_{3}/{k}_{\text{B}}=\ensuremath{-}78.5$ K) is much stronger than the intrachain interactions (${J}_{1}/{k}_{\text{B}}=\ensuremath{-}1.0$ K and ${J}_{2}/{k}_{\text{B}}=6.3$ K), showing surprising ``dimerization'' of magnetic ions caused by the large $3d$-orbital overlap along the Ni1-Ni1 bond. Thus a ``$\text{dimer}+\text{monomer}$'' model is proposed to describe the magnetization process---the 1/2 plateau pertains to weakly coupled Ni2 monomers while the 3/4-like plateau to the strongly coupled Ni1 dimers. The possible supersolid phases from the Ni1 dimers are proposed.