Experimental study in the development of HTS NMR probe

Abstract

We investigated the effect of introducing artificial pinning centers (APCs) into YBa2Cu3O7-δ (YBCO) thin films to improve the critical current density (Jc) and reduce the microwave surface resistance (Rs) in a high dc magnetic field. Introduction of the APC was realized by dispersing BaHfO3(BHO) particulates in the YBCO thin films. Four types of sintered YBCO ceramics with x wt % (x = 0.5, 1.0, 2.0) BHO were used as laser targets in order to fabricate YBCO thin films with various amounts of BHO and investigate the influence of the BHO doping concentration. Jc was measured by a four probe method. We measured Jc in a magnetic field which was applied parallel to the c-axis (Jc(p)), and Jc in a magnetic field which was applied perpendicular to the c-axis (Jc(n)). The Rs was calculated using a correlating equation of Jc and Rs. The Jc(p) at 5 T and 20 K of 1.5 wt% BHO doped YBCO thin film was the largest at 3.4 MA/cm2. The Jc(n) of 1.5 wt% BHO doped YBCO thin film was 2.5 MA/cm2 which is comparable to non-doped. The Rs(n) and Rs(p) of all YBCO thin films was less than 25 μΩ at 500 MHz. Therefore, we clarified the possibility that the most effective way to fabricate thin film for NMR coil application is by doping YBCO with BHO 1.5 wt%.