Takahiro Arayashiki's research while affiliated with Iwate University and other places

So far there have been few reports on high trapped fields for a large superconducting bulk because of large electromagnetic force and insufficient homogeneity. In this paper, the temperature dependence of trapped field for one large crystal of Gd-Ba-Cu-O 46 mm in diameter was empirically investigated. The sample was not broken even in the 10 T field-cooling, implying that the sample quality is excellent in spite of the large size. The trapped field measured at the sample surface was 9.1 T at 42 K, but it can be estimated approximately 13 T by extrapolating the experimental data over 60 K.

Pulsed field magnetization (PFM) was performed for the MgB2 bulk 30 mm in diameter and the applied pulsed-field dependence of the trapped field BC T, temperature rise ΔT and time dependence of the local field BC L (t) were measured on the bulk. BC T = 0.71 T was achieved at 14 K after applying the pulsed field of Bex = 1.55 T, where ΔT of about 10 K was observed. Numerical simulation of PFM was also performed and BC T,ΔT andBC L (t) were simulated. The results of the simulation reproduced the experimental ones qualitatively. The flux dynamics and the heat generation in the MgB2 bulk during PFM were in clear contrast with those in REBaCuO bulks because of a small specific heat, large thermal conductivity, and narrow temperature margin against the transition temperature Tc.

We measured the profiles of the trapped field, BT, on a thin Gd-Ba-Cu-O superconducting bulk plate with 45 mm in diameter and 2 mm in thickness magnetized by the pulsed field, where Gd-Ba-Cu-O consists of a superconducting matrix phase of GdBa2Cu3O7−δ and a nonsuperconducting secondary phase of Gd2BaCuO5. The vortices were mainly trapped at the periphery in the growth sector regions (GSRs) for low applied fields, and around the growth sector boundaries (GSBs) and under the seed crystal (SC) position for high applied fields. The irreversibility line, which was determined from the resistivity measurements, of the sample cut from the GSR was rather lower than those of the samples cut from the GSBs and the SC position. This result revealed the weak vortex pinning strength in the GSRs and was consistent with the BT profiles by PFM. The obtained results suggest that the resistivity can also probe the distribution of the vortex pinning strength.

Pulsed field magnetization (PFM) was performed for the first time on a large MgB2 bulk 50 mm diameter fabricated by a reactive liquid Mg infiltration (Mg-RLI) method, and the time dependence of the local field BL{}C(t) and the trapped field profiles were measured. The trapped field of Bz=0.47 T and the total trapped flux of Φ=0.50 mWb were achieved at Ts=23 K and both values decreased with increasing temperature Ts. The experimental results can be qualitatively reproduced by numerical simulation using electromagnetic and thermal fields for PFM. The flux dynamics and the heat generation/propagation in the MgB2 bulk during PFM were in clear contrast with those in REBaCuO superconducting bulks because of the large thermal conductivity, small specific heat, and narrow temperature margin against the transition temperature Tc.

Pulsed field magnetization (PFM) was performed for the first time on a large MgB2 bulk 50 mm diameter fabricated by a reactive liquid Mg infiltration (Mg-RLI) method, and the time dependence of the local field BLC(t) and the trapped field profiles were measured. The trapped field of Bz=0.47 T and the total trapped flux of Φ=0.50 mWb were achieved at Ts=23 K and both values decreased with increasing temperature Ts. The experimental results can be qualitatively reproduced by numerical simulation using electromagnetic and thermal fields for PFM. The flux dynamics and the heat generation/propagation in the MgB2 bulk during PFM were in clear contrast with those in REBaCuO superconducting bulks because of the large thermal conductivity, small specific heat, and narrow temperature margin against the transition temperature Tc.

Square GdBaCuO bulks with 45.2 × 45.2 mm2 in the ab-plane and 15 mm in thickness along the c-axis with different arrangements of growth sector boundaries (GSBs) were magnetized by a field-cooled magnetization (FCM), a zero-field cooled magnetization (ZFC), and a pulsed-field magnetization (PFM) and the trapped field profiles were measured. For the lower applied field in ZFC, the magnetic flux was trapped in the growth sector regions (GSRs), independent of the arrangement of GSBs. For the lower applied field in PFM, the magnetic flux was mainly trapped in the GSRs and an additional flux was also trapped at the sides in both bulks because of the complicated flux intrusion by the local heat generation. These bulks can trap a magnetic field as high as 7.5 T at 50 K by FCM without destruction. The magnetic flux intrusion and trapping for the square bulks were discussed.

Square GdBaCuO bulks with 45.2 ×45.2 mm² in the ab-plane and 15 mm in thickness along the c-axis with different arrangements of growth sector boundaries (GSBs) were magnetized by a field-cooled magnetization (FCM), a zero-field cooled magnetization (ZFC), and a pulsed-field magnetization (PFM) and the trapped field profiles were measured. For the lower applied field in ZFC, the magnetic flux was trapped in the growth sector regions (GSRs), independent of the arrangement of GSBs. For the lower applied field in PFM, the magnetic flux was mainly trapped in the GSRs and an additional flux was also trapped at the sides in both bulks because of the complicated flux intrusion by the local heat generation. These bulks can trap a magnetic field as high as 7.5 T at 50 K by FCM without destruction. The magnetic flux intrusion and trapping for the square bulks were discussed.

We measured the trapped field profiles on a ∅45 mm GdBCO superconducting bulk plate of 2 mm thickness magnetised using pulsed field magnetisation (PFM), zero-field-cooled magnetisation (ZFC) and field-cooled magnetisation (FCM). The profiles were compared with the distribution of the absolute value of the critical current density (Jc) estimated by the magnetisation measurements using small pieces cut from the bulk plate. The Jc value was enhanced about 20% below the seed crystal compared with that in the growth sector regions (GSRs). The Jc value was also slightly enhanced on the growth sector boundaries (GSBs). For a lower applied pulsed field than that for full magnetisation for PFM, a small amount of the magnetic flux was preferentially trapped at the lower Jc region around the bulk periphery, which was not necessarily similar to that by ZFC. For a higher applied pulsed field, the magnetic flux was finally trapped below the seed crystal and at the GSBs.