Influence of Al doping on the critical fields and gap values in magnesium diboride single crystals
Influence of Al doping on the critical fields and gap values in magnesium diboride single crystals
The lower $({H}_{c1})$ and upper $({H}_{c2})$ critical fields of ${\mathrm{Mg}}_{1\ensuremath{-}x}{\mathrm{Al}}_{x}{\mathrm{B}}_{2}$ single crystals (for $x=0$, $0.1$, and $\ensuremath{\gtrsim}0.2$) have been deduced from local magnetization and specific heat measurements, respectively. We show that ${H}_{c1}$ and ${H}_{c2}$ are both decreasing with increasing doping content. The corresponding anisotropy parameter ${\ensuremath{\Gamma}}_{{H}_{c2}}(0)={H}_{c2}^{ab}(0)∕{H}_{c2}^{c}(0)$ value also decreases from …