Ginzburg-Landau parameters for an ErRh 4 B 4 single crystal

The generalized Ginzburg-Landau parameters ${\ensuremath{\kappa}}_{1}$ and ${\ensuremath{\kappa}}_{2}$ have been determined for the primitive tetragonal phase of ${\mathrm{ErRh}}_{4}$${\mathrm{B}}_{4}$ from magnetization curves of a single-crystal sphere. Along the magnetically hard c direction, ${\ensuremath{\kappa}}_{1}$\ensuremath{\simeq}${\ensuremath{\kappa}}_{2}$=4.5 near ${T}_{c}$, but rise gently with decreasing temperature to a value of 6 as the ferromagnetic transition temperature ${T}_{f}$ is approached. Along the magnetically easy a direction, ${\ensuremath{\kappa}}_{1}$\ensuremath{\simeq}4.5 at ${T}_{c}$ but drops anomalously as ${T}_{f}$ is approached, reflecting the tendency of the system to a type-I superconductor. Furthermore, along the c direction where the effect of magnetism is mild and the system behaves similar to an ordinary type-II superconductor, the penetration depth \ensuremath{\lambda}(0) and the coherence distance \ensuremath{\xi}(0) are estimated to be 830 and 180 A\r{}, respectively.