Addition of Ho2O3 of different types to MgB2 in the ex-situ Spark Plasma Sintering: Simultaneous control of the critical current density at low and high magnetic fields

Two different types of Ho2O3 powders (showing a much different morphology) were added to MgB2 in the ex-situ Spark Plasma Sintering (SPS). In the 5-25 K range, the first Ho2O3 powder type does not significantly suppress the critical current density Jc at low magnetic fields and the second one enhances it at high fields, while their mixture simultaneously controls Jc at both small and high magnetic fields so that the decrease is small at low fields and there is a notable enhancement at high fields when compared to pristine sample. The control of Jc(H) is discussed versus specific characteristics of the raw powders, the resulting microstructure of the added SPS-ed samples and pinning details from magnetic relaxation measurements.