Anisotropic Superconducting Properties of Aligned MgB2 Crystallites

Samples of aligned ${\mathrm{MgB}}_2$ crystallites have been prepared, allowing for the first time the direct identification of an upper critical field anisotropy $H_{c2\mathrm{}}^{\mathrm{ab}}{/H}_{c2\mathrm{}}^c={\xi }_{\mathrm{ab}}/{\xi }_c\simeq 1.7$, with ${\xi }_{o,ab}\simeq 70Å$, ${\xi }_{o,c}\simeq 40Å$, and a mass anisotropy ratio $m_{\mathrm{ab}}{/m}_c\simeq 0.3$. A ferromagnetic background signal was identified, possibly related to the raw materials purity.