Quantum Magnetism in Fe2Cu2 Polymeric Branched Chains: Insights from Exactly Solved Ising-Heisenberg Model

TL;DR

This paper investigates the quantum magnetic properties of Fe2Cu2 polymeric chains using an exactly solved Ising-Heisenberg model, revealing distinct magnetic phases, entanglement behavior, and agreement with experimental data.

Contribution

It provides a rigorous theoretical analysis of the magnetic phases and entanglement in Fe2Cu2 chains using an exactly solvable model, connecting theory with experimental observations.

Findings

Identified three magnetic phases: quantum antiferromagnetic, quantum ferrimagnetic, and classical ferromagnetic.

Observed magnetization plateaus at zero and half saturation, with full saturation in the ferromagnetic phase.

Found thermal entanglement persists up to 224 K and is influenced by magnetic fields.

Abstract

The spin-1/2 Ising-Heisenberg branched chain, inspired by the magnetic structure of three isostructural polymeric coordination compounds [(Tp)2Fe2(CN)6X(bdmap)Cu2(H2O)].H2O to be further denoted as Fe2Cu2 (Tp = tris(pyrazolyl)hydroborate, bdmapH = 1,3-bis(dimethylamino)-2-propanol, HX = acetic acid, propionic acid or trifluoroacetic acid), is rigorously studied using the transfer-matrix method. The overall ground-state phase diagram reveals three distinct phases: a quantum antiferromagnetic phase, a quantum ferrimagnetic phase and a classical ferromagnetic phase. In the zero-temperature magnetization curve, two quantum ground states are manifested as intermediate plateaus at zero and half of the saturation magnetization, while the magnetization reaches its saturated value within the classical ferromagnetic phase. The bipartite entanglement between nearest-neighbor Heisenberg spins is more pronounced in the quantum ferrimagnetic phase compared to the quantum antiferromagnetic phase due to a fully polarized nature of the Ising spins. A reasonable agreement between theoretical predictions for the spin-1/2 Ising-Heisenberg branched chain and experimental data measured for a temperature dependence of the magnetic susceptibility and a low-temperature magnetization curve suggests strong antiferromagnetic coupling between nearest-neighbor CuII-CuII magnetic ions and moderately strong ferromagnetic coupling between nearest-neighbor CuII-FeIII magnetic ions in the polymeric compounds Fe2Cu2. A thermal entanglement between nearest-neighbor CuII-CuII magnetic ions persists up to a relatively high threshold temperature T = 224 K and undergoes a transient magnetic-field-driven strengthening.