AC susceptometry on the single-molecule magnet Ni2Dy

Molecular nanomagnets are molecules which show novel and fascinating magnetic properties. The best known phenomenon is the observation of magnetic hysteresis on the molecular scale in the single-molecule magnets (SMMs), such as Mn12ac. In addition, quantum mechanical effects, such as the tunneling of the magnetization, can be observed in bulk samples of SMMs. A key goal for understanding the underlying physics is the measurement of the magnetization dynamics, which can be accomplished using ac susceptometry. However, the magnetic moments of samples of SMMs are weak since the volume density of the magnetic ions is very small as compared to e.g. inorganic compounds. In this talk we will describe the construction of an ac susceptometer suitable for investigating molecular nanomagnets. A particular goal was to reach frequencies of the ac field of 100 kHz, extending the frequency range of commercial devices typically used in this research area by two decades. The device can be operated in the temperature range of 1.5 to 300 K and was characterized by comparing data recorded on Mn19 with available literature results. Lastly, we will present our experimental results on the novel SMM Ni2Dy and discuss the different magnetic relaxation regimes observed in it.