Magnetization plateau in diamond chains with delocalized interstitial spins

Several low-dimensional magnetic compounds exhibit magnetization plateaus as a result of the interplay between frustration and quantum fluctuations. Here, we investigate the thermodynamic properties of diamond chains on which competing interactions emerge from the local quantum hopping of interstitial S=1/2 spins which are intercalated between nodal Ising spins. Using an exact diagonalization and the decoration-iteration transformation, we compute the temperature and external field dependences of the magnetization, specific heat, susceptibility, and the full ground state phase diagram. Magnetization plateaus of 1/3 are observed and related to field-driven transitions among four possible ground states: saturated paramagnetic, unsaturated paramagnetic, ferrimagnetic, and nodal antiferromagnetic. There is a range of hopping amplitudes and exchange mismatches for which the 1/3 magnetization plateau occurs between finite values of the external field. The specific heat and magnetic susceptibility also show signatures of the competition between the possible ground states.