Anisotropy of superconductivity from MgB2 single crystals

Magnesium diboride $({\mathrm{MgB}}_{\mathrm{2}})$ single crystals, with a maximum size of $\text{0.5×0.5×0.02}$ ${\mathrm{mm}}^{\mathrm{3}},$ were grown by the vapor transport method in a sealed molybdenum crucible. A superconducting transition with the onset temperature of 38.6 K was confirmed by both transport and magnetization measurements. The upper critical field anisotropy ratio, $H_{\text{c2}}^{\mathrm{\parallel ab}}{\text{(0)/H}}_{\text{c2}}^{\mathrm{\parallel c}}\text{(0),}$ was estimated to be 2.6 from the magnetic field-temperature phase diagram for ${\mathrm{MgB}}_{\mathrm{2}}$ single crystals.