Ground-state phases in antiferromagnetic spin-crossover chains

TL;DR

This paper provides a comprehensive theoretical analysis of the ground-state phases in one-dimensional antiferromagnetic spin-crossover chains, revealing complex phase behavior including novel periodic states and a dimer phase.

Contribution

It presents the complete ground-state phase diagram of spin-crossover chains considering various interactions, using high-precision density-matrix renormalization group calculations, and identifies new periodic phases.

Findings

Identification of multiple ground-state phases including pure and mixed states.

Discovery of a dimer phase stabilized by singlet formation.

Detailed phase diagram considering elastic, magnetic, and external field effects.

Abstract

Spin-crossover molecules having a low-spin ground state and a low-lying excited high-spin state are promising components for molecular electronics. We theoretically examine one-dimensional spin-crossover chain molecules of the type of Fe-II triazole complexes. The existence of the additional low-spin/high-spin degree of freedom leads to rich behavior already in the ground state. We obtain the complete ground-state phase diagram, taking into account an elastic nearest-neighbor interaction, a ferromagnetic or antiferromagnetic exchange interaction between the magnetic ions, and an external magnetic field. Ground-state energies are calculated with high numerical precision using the density-matrix renormalization group. Besides pure low-spin, highspin, and alternating low-spin/high-spin phases we obtain a number of periodic ground states with longer periods, which we discuss in detail. For example, for antiferromagnetic coupling there exists a dimer phase with a magnetic unit cell containing two high-spin ions forming a spin singlet and a single low-spin ion, which is stabilized by the energy gain for singlet formation.