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Hysteresis in Transport Critical-Current Measurements of Oxide Superconductors

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ABSTRACT

We have investigated magnetic hysteresis in transport critical-current (Ic) measurements of Ag-matrix (Bi,Pb)2Sr2Ca2Cu3O10–x (Bi-2223) and AgMg-matrix Bi2Sr2CaCu2O8+x (Bi-2212) tapes. The effect of magnetic hysteresis on the measured critical current of high temperature superconductors is a very important consideration for every measurement procedure that involves more than one sweep of magnetic field, changes in field angle, or changes in temperature at a given field. The existence of this hysteresis is well known; however, the implications for a measurement standard or interlaboratory comparisons are often ignored and the measurements are often made in the most expedient way. A key finding is that Ic at a given angle, determined by sweeping the angles in a given magnetic field, can be 17 % different from the Ic determined after the angle was fixed in zero field and the magnet then ramped to the given field. Which value is correct is addressed in the context that the proper sequence of measurement conditions reflects the application conditions. The hysteresis in angle-sweep and temperature-sweep data is related to the hysteresis observed when the field is swept up and down at constant angle and temperature. The necessity of heating a specimen to near its transition temperature to reset it to an initial state between measurements at different angles and temperatures is discussed.

No MeSH data available.


Ic/Ic(virgin 90°) at 0.1 µV/cm versus angle around 90° for the Bi-2212 specimen at 4 K for various sweep directions and magnetic fields: (a) 0.2 T, (b) 1 T, (c) 5 T.
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f27-j64goo: Ic/Ic(virgin 90°) at 0.1 µV/cm versus angle around 90° for the Bi-2212 specimen at 4 K for various sweep directions and magnetic fields: (a) 0.2 T, (b) 1 T, (c) 5 T.

Mentions: An additional minor angle sweep around 90° was made after each of the previous sets of data. These minor sweeps are shown on Figs. 27–29. The branch sequence is given in the legend of each plot. For each plot, the first branch was taken going from 90° to 110°, thus continuing in the same direction as the previous data, which was from −90° to 90°. The bumps when approaching 90° from each side are nearly symmetric. As the amount of the hysteresis decreases, all branches approach the virgin values. Using the symmetry of virgin values for the 4 K and 20 K plots and the sweep branches for all of these plots, the center of symmetry seems to be between 91° and 92°. As stated earlier, this could be due to a slight error in the initial alignment of the cryostat.


Hysteresis in Transport Critical-Current Measurements of Oxide Superconductors
Ic/Ic(virgin 90°) at 0.1 µV/cm versus angle around 90° for the Bi-2212 specimen at 4 K for various sweep directions and magnetic fields: (a) 0.2 T, (b) 1 T, (c) 5 T.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4862823&req=5

f27-j64goo: Ic/Ic(virgin 90°) at 0.1 µV/cm versus angle around 90° for the Bi-2212 specimen at 4 K for various sweep directions and magnetic fields: (a) 0.2 T, (b) 1 T, (c) 5 T.
Mentions: An additional minor angle sweep around 90° was made after each of the previous sets of data. These minor sweeps are shown on Figs. 27–29. The branch sequence is given in the legend of each plot. For each plot, the first branch was taken going from 90° to 110°, thus continuing in the same direction as the previous data, which was from −90° to 90°. The bumps when approaching 90° from each side are nearly symmetric. As the amount of the hysteresis decreases, all branches approach the virgin values. Using the symmetry of virgin values for the 4 K and 20 K plots and the sweep branches for all of these plots, the center of symmetry seems to be between 91° and 92°. As stated earlier, this could be due to a slight error in the initial alignment of the cryostat.

View Article: PubMed Central - PubMed

ABSTRACT

We have investigated magnetic hysteresis in transport critical-current (Ic) measurements of Ag-matrix (Bi,Pb)2Sr2Ca2Cu3O10–x (Bi-2223) and AgMg-matrix Bi2Sr2CaCu2O8+x (Bi-2212) tapes. The effect of magnetic hysteresis on the measured critical current of high temperature superconductors is a very important consideration for every measurement procedure that involves more than one sweep of magnetic field, changes in field angle, or changes in temperature at a given field. The existence of this hysteresis is well known; however, the implications for a measurement standard or interlaboratory comparisons are often ignored and the measurements are often made in the most expedient way. A key finding is that Ic at a given angle, determined by sweeping the angles in a given magnetic field, can be 17 % different from the Ic determined after the angle was fixed in zero field and the magnet then ramped to the given field. Which value is correct is addressed in the context that the proper sequence of measurement conditions reflects the application conditions. The hysteresis in angle-sweep and temperature-sweep data is related to the hysteresis observed when the field is swept up and down at constant angle and temperature. The necessity of heating a specimen to near its transition temperature to reset it to an initial state between measurements at different angles and temperatures is discussed.

No MeSH data available.