Microwave Properties of BaFe 1.9 Ni 0.1 As 2 Superconducting Single Crystal

High quality BaFe 2− x Ni x As 2 superconducting single crystals have been successfully grown by the self-flux method. Two types of equipment were developed for microwave measurements at X-band and Ka-band, respectively. The first one is a sapphire dielectric cavity. The sample is supported by a sapphire rod in the center of this cavity. The other one is designed by using Quasi-optic Dielectric Resonators (QDR) cells. The superconducting sample to be measured is mounted inside the cell. These two systems are sealed in similar but different vacuum chambers, respectively, and soaked in the liquid 4 He. The temperature of samples can be controlled from 1.6 to 30 K. Frequency dependent microwave properties of BaFe 1.9 Ni 0.1 As 2 were studied systematically. Temperature dependence of transmission response and Q-factor were measured by a network analyzer (Agilent N5230C). The results showed an evidence of multigap structure as the normalized changes in the surface reactance and the corresponding normalized changes in the in-plane penetration depth have power dependence of temperature at low temperature.