GoldExI : FAQ : Self Field

Question

How to remove self-field from Ic(H) plot?
How to remove series resistance from IVC?

Answer

To remove Self-Field (SF) from Ic(H) dependence(s), choose Math|Self-Field in main menu. You have possibility to remove SF using several options:

Automatically process all curves, finding self-field coefficient for every curve separately. The curves which do not look like Ic(H) dependances will be skipped.
Automatically process 2 curves: Ic(H) and -Ic(H). This option calculates self-field, H-shift and I-shift. These values are common for both curves. Push OK to get rid of all 3 of them.
Manually process all curves. Input the values of current and field (or just a coefficient) to compensate the field. Note, that initial value of coefficient is the one used for previous self-field removal.

Choose one of this options. The auto-algorithms work only with curves which look Fraunhofer-like i.e. they shift maximum of current to the point where H=0. The manual algorithm works for any curve. For manual algorithm you can input either "The current of XXX mA induces the field of YYY mA" or specify self-field coefficient YYY/XXX directly. You can use "calc" button to calculate SF-coefficient from YYY and XXX.

You can also remove self field only from one curve. In this case right-click the curve and keep the button pressed until context menu appears. Then in context menu choose Selected Curve(s)|Self Field. In this case maximum current and corresponding induced field will be calculated automatically from curve data and shown in the window. You can just push "Ok", or you can input your own values. Note, that offered value of SF coefficient refers to the previous SF removal.

Tip: As you understand, the auto-algorithms do not work correctly for Ic(H) of annular junction with trapped fluxon(s) because at H=0 there is no maximum. For this case I suggest to do the following. Open Ic(H) for no trapped fluxons, remove self-filed using auto-mode, open Ic(H) for 1 trapped fluxon, and remove self filed using manual mode with SF coefficient from the previous self-field removal. By the way, you don't have to input this SF coefficient manually -- GoldExI remembers the last one. :-)

Tip: Although this function of GoldExI is called Self-Field removal, it can also be used to remove (parasitic) series resistance from IVC e.g. when one measures using 2-points instead of 4-points. In this case SF-coefficient is just resistance which you need to subtract. ;-) In this case use manual mode only.