Magnetization of potassium-doped p -terphenyl and p -quaterphenyl by high-pressure synthesis

Abstract

By using the high pressure synthesis method, we fabricated the potassium-doped para-terphenyl. The temperature dependence of magnetization measured in both zero-field-cooled and field-cooled processes shows step-like transitions at about 125 K. This confirms an earlier report about the possible superconductivity-like transition in the same system. However, the magnetization hysteresis loop exhibits a weak ferromagnetic background. The estimate on the diamagnetization of this step shows that the diamagnetic volume is only about 0.04% at low temperatures, if we assume that the penetration depth is much smaller than the size of possible superconducting grains. This magnetization transition does not shift with magnetic field, but is suppressed and becomes almost invisible above 1.0 T. The resistivity measurements fail because of an extremely large resistance. By using the same method, we also fabricated the potassium-doped para-quaterphenyl. A similar step-like transition at about 125 K was also observed by using a magnetization measurement. Since there is an unknown positive background and the diamagnetic volume is too small, it is insufficient to conclude that this step is derived from superconductivity although it appears so.