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In this study, the local magnetic relaxation properties of GdBa2Cu3O7-δ (GdBCO) coated conductor were investigated using low-temperature scanning Hall probe microscopy (LTSHPM).
The loss of alternating current remains a problem in high-temperature superconductors; however, it can be reduced when the superconductor is processed into filaments as alternating current loss is related to the width of the sample. Here, samples were patterned into filaments by photolithography and processed into single, double, and triple strips placed in parallel. In addition, two types of double and triple strip samples were considered: connected and unconnected.
First, the local magnetic relaxation of patterned samples with various shapes is presented, and the features of local magnetic relaxation dependent on the sample shape are described. In addition, the local magnetic relaxation was compared with data obtained using a magnetic property measurement system (MPMS), showing the average magnetic relaxation rate of an entire sample with one value, and characterizing each sample with different relaxation rates at each position.
Next, the thermal activation energies of single and double strips were calculated from the magnetic relaxation data. Various models suggest methods different methods to calculate thermal activation energy; however, in this study, the thermal activation energy was calculated from the diffusion equation without reference to a specific model. The variation of activation energy with time and position is described.
Finally, the proportional relations between the remanent field, hysteresis loss, and magnetic relaxation are provided. Thin-film samples were used in these experiments; however, there is no appropriate equation for thin films. Therefore, a mathematical relation was derived by taking a thin-film approximation of the formula for a disc-shaped cylinder.
Thesis Advisor: Prof. Hyeong-Cheol Ri