The polymer phase of the TDAE-C$_{60}$ organic ferromagnet

TL;DR

This study investigates the pressure-induced polymerization and magnetic properties of TDAE-C60, revealing a stable polymeric phase with ferromagnetic to paramagnetic transition and temperature-dependent spin activity.

Contribution

It provides the first detailed ESR analysis of the polymeric phase of TDAE-C60 and its stability, depolymerization temperature, and magnetic behavior.

Findings

Polymeric phase stable after pressure release.

Ferromagnetic to paramagnetic transition at 7 kbar.

Unpaired spins become ESR-active above 320 K.

Abstract

The high-pressure Electron Spin Resonance (ESR) measurements were preformed on TDAE-C$_{60}$ single crystals and stability of the polymeric phase was established in the $P - T$ parameter space. At 7 kbar the system undergoes a ferromagnetic to paramagnetic phase transition due to the pressure-induced polymerization. The polymeric phase remains stable after the pressure release. The depolymerization of the pressure-induced phase was observed at the temperature of 520 K. Below room temperature, the polymeric phase behaves as a simple Curie-type insulator with one unpaired electron spin per chemical formula. The TDAE$^+$ donor-related unpaired electron spins, formerly ESR-silent, become active above the temperature of 320 K and the Curie-Weiss behavior is re-established.