Heterobimetallic Dy-Cu coordination compound as a classical-quantum ferrimagnetic chain of regularly alternating Ising and Heisenberg spins

TL;DR

This paper analyzes a classical-quantum spin chain model with alternating Ising and Heisenberg spins, revealing complex phase behavior and magnetization properties that match experimental data for a specific heterobimetallic compound.

Contribution

It introduces an exact solution for a mixed Ising-Heisenberg chain considering local anisotropy axes and connects theoretical predictions with experimental observations.

Findings

Four distinct ground-state phases identified.

Presence of 'half-fire, half-ice' degenerate state.

Magnetization curves show smooth dependence due to canting angle.

Abstract

A classical-quantum chain composed of regularly alternating Ising and Heisenberg spins is rigorously solved by considering two distinct local anisotropy axes of the Ising spins. The ground-state phase diagram and magnetization curves are examined depending on a spatial orientation of the applied magnetic field. The phase diagram totally consists of four distinct phases and a few macroscopically degenerate points, where an outstanding coexistence of perfect order and complete disorder occurs within the so-called 'half-fire, half-ice' state. The zero-temperature magnetization curves generally exhibit a smooth dependence on a magnetic field owing to a canting angle between two coplanar anisotropy axes of the Ising spins, which enforces a misalignment of the magnetization vector from a direction of the applied magnetic field. It is evidenced that the investigated spin-chain model reproduces magnetic features of the heterobimetallic coordination compound Dy(NO)$_{3}$(DMSO)$_{2}$Cu(opba)(DMSO)$_{2}$ (DMSO=dimethylsulfoxide, opba=orthophenylenebisoxamato). The high-field magnetization data reported for the powder sample of this polymeric coordination compound generally display a substantial smoothing on account of a powder averaging.