Observation of flux distribution on the surface of MPMG-processed YBCO

Abstract

A macroscopic observation of a magnetic flux distribution on the surface of a superconducting bulk material was performed. First, a single-domained thin rectangular YBCO sample (10 mmxl0mmxlmm) was field-cooled in liquid nitrogen. After the applied field was turned off, a field distribution in the area of lOmmxlOmm was mapped by scanning the sample surface at intervals of 0. 5" using a Hall probe fixed to a XY-stage. The obtained field distribution was visualized into a three-dimensional distribution map and a twodimensional contour graph. The overall shape of the field distribution had a four-fold symmetry reflected by the sample geometry. Next, assuming that the critical current density J , is independent of the field strength, a field distribution generated by square current loops was calculated numerically. The intragranular J, was estimated to be 2.6x1@A/cm2 (77K, OT) by fitting the calculated profile to the measured profile. Finally, it is found that the measurement of field distributions on the surface of a superconductor using a Hall probe is applicable to an estimation of an ntragranular J , for a superconductor without destroying the samples.

Superconducting properties of natural and artificial grain boundaries in bulk melt-textured YBCO

“…Another possible approach for evaluating the behaviour of grain boundaries in YBCO pellets is to measure the trapped flux by scanning a miniature Hall probe over the top surface of the sample [11][12][13][14][15]. Such measurement techniques are increasingly popular since they are non-destructive and may be applied to large samples.…”

A flux extraction device to measure the magnetic moment of large samples; application to bulk superconductors

“…(6) and (8). According to the latter relation, it is tempting to setẑ to a root value of F o in order to reject the relative error to a still higher order (note that the hexadecapole contribution is also rejected given that it is associated with an even profile function).…”

“…5 Associated measurement and characterization methods by both destructive and non-destructive techniques have developed naturally as the ability to melt process these materials has evolved. Of these, the most popular methods have tended to focus on local measurements of the flux density by scanning a miniature Hall probe above the top surface of the sample, either after full magnetization of the sample by a field cooling technique [6][7][8] or by using a small permanent magnet moved simultaneously with the Hall probe (the so-called "magnetoscan" technique). 9 Such measurement techniques have provided valuable information about current distribution and characteristics in the vicinity of the surface of the sample, although they are significantly less sensitive to the inner, bulk critical current density.…”

Study by Hall probe mapping of the trapped flux modification produced by local heating in YBCO HTS bulks for different surface/volume ratios

“…Such trapped fields suggest that single-domain HTSs may replace permanent magnets in the rotor of an AC rotating machine in order to achieve a high torque [1,4]. The most common characterization technique of such samples consists in mapping the sample top surface with a miniature Hall probe [5][6][7][8][9]. In such a measurement, the sample is always kept at a uniform temperature.…”

“…At present, the most promising materials are bulk (RE)BCO single domains (where RE denotes a rare earth element such as Y, Dy, Nd...), for which trapped induction values exceeding 15 T have been successfully demonstrated by various laboratories [3], Such trapped fields suggest that single-domain HTSs may replace permanent magnets in the rotor of an AC rotating machine in order to achieve a high torque [1,4]. The most common characterization technique of such samples consists in mapping the sample top surface with a miniature Hall probe [5][6][7][8][9]. In such a measurement, the sample is always kept at a uniform temperature.…”