Anisotropy of<tex>$rm J_rm c$</tex>in Ex Situ<tex>$rm MgB_2/rm Fe$</tex>Monofilamentary Tapes

Abstract

The anisotropy of the critical current density of Fe-sheathed ex situ MgB 2 monofilamentary tapes has been measured at various magnetic fields and temperatures and has been found to be influenced by the particle size of the starting material. Already reacted powders were milled in order to obtain different starting particle sizes. In order to understand the origin of the anisotropy, we have undertaken an X-ray study on the degree of texturing in the filaments after mechanical removal of the Fe sheath. The degree of texturing of the filaments at the interface Fe MgB 2 and at the center of the filaments has been determined.A moderate texture has been found, being slightly higher at the interface.Index Terms-Critical current density, critical current density anisotropy, ex situ tapes, MgB 2 .

The effects of attrition and ball milling on the properties of magnesium diboride

“…Selected representative spectra for 2 ranges including peaks due to MgO and MgB 4 are shown in Figure 7. MgB 4 peaks are largest and most prevalent in powders with high MgO contents, yet were not present in the XRD spectra of the starting powder, indicating that MgB 2 breaks down to form MgO and MgB 4 during heat treatment, in agreement with observations by Lezza et al [31]. MgB 4 was not detected in every spectrum, while measurable levels of MgO were observed in all spectra.…”

Improvement of current density by texture andIcanisotropy in thin filament MgB2/Fe tapes

“…So far, several authors have presented the anisotropy of I c for flattened MgB 2 ex situ and in situ wires [11][12][13][14], which is attributed to the texture of the MgB 2 core close to the metal sheath interface. Consequently, the critical current (I c ) measured in a parallel external field is systematically higher than that in a perpendicular one and the anisotropy factor is usually expressed as k a = I c−par /I c−perp , where I c−par is the critical current measured for the external field parallel to the flat side of the tape and I c−perp for the perpendicular field orientation.…”

“…The factor k a increases with the magnitude of the external field. The value of k a directly reflects the average c-axis grain alignment of the MgB 2 core which is influenced by the deformation used, the sheath material [11,12] and the particle size of the precursor powder [13]. A typical anisotropy factor of about 10 is usually measured for single core ironsheathed MgB 2 tape with aspect ratio (width to thickness) b/a = 10 in an external field of 7 T and temperature 4.2 K. A recent publication has shown I c anisotropy of in situ tapes with different sheath materials [14].…”

Effect of fabrication route on density and connectivity of MgB2filaments

“…This is anticipated since higher pressure increases the texturing of the filament thus leading to higher anisotropy. For all I and M samples, the Γ values are below 1.7 at 7 T which are usual values for MgB 2 tapes [19], [21]- [22]. This was expected because the extent of the applied deformations was not very intensive due to the fairly small starting diameter of the Ti tube and its softness after annealing.…”