# $S$ =1/2 ferromagnetic Heisenberg chain in a verdazyl-based complex

## TL;DR

This study introduces a new verdazyl-based complex as a model for an $S$=1/2 ferromagnetic Heisenberg chain, demonstrating its magnetic properties and phase transition behaviors through experimental and theoretical analysis.

## Contribution

The paper provides the first experimental realization and detailed analysis of an $S$=1/2 ferromagnetic Heisenberg chain using a verdazyl-based complex, including magnetic and thermodynamic properties.

## Key findings

- The compound exhibits predominant ferromagnetic interactions forming an $S$=1/2 chain.
- A phase transition to antiferromagnetic order occurs due to interchain couplings.
- Magnetic susceptibility and specific heat behaviors are consistent with the ferromagnetic Heisenberg chain model.

## Abstract

We present a model compound for the $S$=1/2 ferromagnetic Heisenberg chain composed of the verdazyl-based complex $[$Zn(hfac)$_2]$$[$4-Cl-$o$-Py-V-(4-F)$_2]$. $Ab$ $initio$ MO calculations indicate a predominant ferromagnetic interaction forming an $S$=1/2 ferromagnetic chain. The magnetic susceptibility and specific heat indicate a phase transition to an AF order owing to the finite interchain couplings. We explain the magnetic susceptibility and magnetization curve above the phase transition temperature based on the $S$=1/2 ferromagnetic Heisenberg chain. The magnetization curve in the ordered phase is described by a conventional AF two-sublattice model. Furthermore, the obtained magnetic specific heat reproduces the almost temperature-independent behavior of the $S$=1/2 ferromagnetic Heisenberg chain. In the low-temperature region, the magnetic specific heat exhibits $\sqrt{T}$ dependence, which is attributed to the energy dispersion in the ferromagnetic chain.