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

Abstract Two different types of Ho 2 O 3 powders (showing a much different morphology) were added to MgB 2 in the ex-situ Spark Plasma Sintering (SPS). In the 5–25 K range, the first Ho 2 O 3 powder type does not significantly suppress the critical current density J c at low magnetic fields and the second one enhances it at high fields, while their mixture simultaneously controls J c 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 J c ( 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.