Magnetic transitions in K-doped biphenyl and p-terphenyl

Recently, the superconductivity in K-doped p-terphenyl was reported with the transition temperatures range from 7 to 123 Kelvin, which attracts much attention. In this work, to investigated the possible magnetism and the transition between magnetism and superconductivity, we have studied the magnetism of K-doped biphenyl and p-terphenyl by combining the first-principles calculations with magnetization measurements. We found that the tilting between two successive benzene rings drives the antiferromagnetic spin ordering of electrons transferred to C atoms from K atoms at the low doping concentration. With the increase of charge transferring, the spin ordering disappears in systems while the superconductivity occurs. Namely, the transition from antiferromagnetic to superconducting behavior occurs with the increase of K doping contents. In fabricated K-doped biphenyl sample, the magnetic susceptibility measurement confirmed the existence of AFM characteristics, which is in good agreement with theoretical predictions. For K-doped p-terphenyl, more experimental observations is needed. Our results is helpful for understanding the superconducting transition in this kind of materials.