Quantum Entanglement in Nitrosyl Iron Complexes

TL;DR

This paper investigates quantum entanglement in nitrosyl iron complexes through magnetic susceptibility measurements, identifying the temperature range where entanglement persists and its increase at lower temperatures.

Contribution

It demonstrates the presence of quantum entanglement in specific iron complexes and models its temperature dependence using magnetic susceptibility data.

Findings

Entanglement exists below 80-120 K in the studied complexes.

Entanglement increases to 90-95% at 25 K in complex II.

Magnetic susceptibility can be used to quantify entanglement in these compounds.

Abstract

Recent magnetic susceptibility measurements for polycrystalline samples of binuclear nitrosyl iron complexes [Fe_2(C_3H_3N_2S)_2(NO)_4] (I) and [Fe_2(SC_3H_5N_2)_2(NO)_4] (II), suggest that quantum-mechanical entanglement of the spin degrees of freedom exists in these compounds. Entanglement E exists below the temperature T_E that we have estimated for complexes I and II to be 80-90 and 110-120 K, respectively. Using an expression of entanglement in terms of magnetic susceptibility for a Heisenberg dimer, we find the temperature dependence of the entanglement for complex II. Having arisen at the temperature T_E, the entanglement increases monotonically with decreasing temperature and reaches 90-95% in this complex at T=25 K, when the subordinate effects are still small.