Evidence of X-Ray Magnetic Circular Dichroism and Low-Field Microwave Absorption in Room-Temperature Organic Ferromagnetic Semiconductor

Abstract

Room-temperature organic ferromagnetic semiconductors represent a promising frontier in developing next-generation electronic and spintronic devices. However, the origin of magnetic moments in organic ferromagnets and the acquisition of critical evidence for magnetic ordering remain incompletely understood. This study presents compelling evidence for room-temperature ferromagnetism in N,N′-diamino perylene bisimide (2NH₂-PBI) radical aggregates through a comprehensive analysis utilizing X-ray magnetic circular dichroism (XMCD), low-field microwave absorption (LFMA) techniques and magnetic characterization. The 2NH₂-PBI samples, prepared via hydrothermal reduction, exhibit a significant saturation magnetization of 0.8 emu g⁻¹ (336.3 emu mol⁻¹) at 300 K, with a coercive field of 170 Oe. The XMCD measurements at the carbon K-edge exhibited a pronounced dichroic signal (~8.7%), confirming the origin of ferromagnetism in the π-conjugated electrons of the perylene core. Density functional theory calculations further support this finding by demonstrating that spin density is primarily delocalized on the π-conjugated skeleton, giving a microscopic explanation for the magnetic properties of 2NH₂-PBI radicals. Furthermore, LFMA studies provide additional evidence of ferromagnetic ordering, showcasing hysteretic behavior consistent with domain wall dynamics. Our work indicates that imide-based radical molecules with extended π-conjugated structures constitute a class of effective magnetic functional units.