Discovery of room temperature ferromagnetism in metal-free organic semiconductors

TL;DR

This study reports the discovery of room temperature ferromagnetism in a metal-free organic semiconductor, demonstrating long-range magnetic order in materials traditionally considered nonmagnetic.

Contribution

It introduces a novel method to induce ferromagnetism in organic semiconductors at room temperature, expanding the potential for organic magnetic devices.

Findings

Ferromagnetism observed above 400 K in organic semiconductor

Saturated magnetization of 0.48 μB per molecule

Ferromagnetism originates from π orbitals of radicals

Abstract

Creating magnetic semiconductors that work at warm circumstance is still a great challenge in the physical sciences. Here, we report the discovery of ferromagnetism in the metal-free perylene diimide semiconductor, whose Curie temperature is higher than 400 Kelvin. A solvothermal approach is used to reduce and dissolve the rigid-backbone perylene diimide crystallites, and radical anion aggregates were fabricated by the subsequent self-assembly and oxidation process. Magnetic measurements exhibit the ferromagnetic ordering with the saturated magnetization of 0.48 $\mu_{\rm B}$ per molecule and the appreciable magnetic anisotropy. X-ray magnetic circular dichroism spectra suggest the ferromagnetism stems from $\pi$ orbitals of radicals. Our findings unambitiously demonstrate the long-range ferromagnetic ordering can survive at room temperature in organic semiconductors, although which are intuitively regarded to be nonmagnetic.