Compact AC/DC susceptometer using a high-temperature superconductor superconducting quantum interference device

We developed a compact susceptometer employing a high-temperature superconductor (HTS) superconducting quantum interference device (SQUID) that can measure M-H characteristics and harmonic components induced in the AC magnetic field response from a sample. In the DC function for measuring M-H characteristics, the sample was vibrated in the DC magnetic field, and the secondary magnetic field generated from the sample was detected by a DC pickup coil. In the AC function for measuring harmonic components, the sample is placed in the AC magnetic field, and the AC response was detected by an AC pickup coil. The pickup coil is connected in series with the input coil, which is inductively connected to the HTS-SQUID. Signal from the HTS-SQUID was transmitted to the lock-in amplifier, and was analyzed as the intensity and phase of the measured magnetic field. In order to clarify the basic properties of the system, we measured the AC magnetic field response from a sample in the case of changing the position between the sample and the pickup coil, and M-H characteristics when changing the DC bias magnetic field intensity. Furthermore, by analyzing the harmonic components of AC/DC magnetic field response, the system is able to measure the magnetic properties with high sensitivity and high speed.