Negative magnetoresistance in organic ionic semiconductor:TTFCOONH3Ph

• Negative magnetoresistance is observed in single crystal of TTFCOONH3Ph at room temperature.
• Magnetization curve of roughly oriented single crystals exhibits a hysteresis loop at room temperature.
• TOF-SIMS analysis verifies trace amount of magnetic impurity in a single crystal of TTFCOONH3Ph.
• Ferromagnetic resonance detects magnetically ordered spins at room temperature.
• An isotope-substituted TTFCOOND3C6D5 shows a role of ionic part in the magnetic properties.

TTFCOONH3Ph is a recently synthesized open-shell ionic semiconductor, the electronic state of which differs from that of typical organic closed-shell semiconductors. Magnetotransport properties were examined using a single-crystal sample, and found to exhibit small negative magnetoresistance (∼0.2%) for 9 T at room temperature (rt). The magnetization curve verifies the existence of a ferromagnetic (35%) and a paramagnetic (65%) component at rt, which is very similar to that of diluted magnetic semiconductors, despite the absence of any ferromagnetic metal elements. Electron spin resonance reveals weak localization of paramagnetic molecular spins, and moreover, ferromagnetic resonance confirms the existence of magnetically ordered spins in addition to the paramagnetic ones. The origin of the spin-polarized transport is discussed.