Magnetic anisotropy in single-crystal rare-earth-dopedRBa2Cu4O8(R=Y, Dy, Gd, Ho, Er, Tm, Yb)

We measured magnetic susceptibility of single-crystal rare-earth-doped R${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_4$ ${\mathrm{O}}_8$ (where R=Y, Dy, Gd, Ho, Er, Tm, Yb) in the normal state along the three principal axes. The anisotropy measured fits well to calculated values obtained from a crystal electric field (CEF) analysis. From our results we developed a general scaling relation for the CEF parameters across the rare-earth series.