Magnetic anisotropy and crystalline electric field in borocarbide superconductors

The magnetic properties of the RNi2B2C (R = Gd, Tb, Dy: Ho, Er, Tm) compounds are presented and studied in terms of the crystalline electric field effect (CEF). All of the compounds containing the magnetic rare earths R = To, Dy, Ho, Er, and Tm exhibit a strong temperature-dependent highly anisotropic magnetic behavior while isotropic for R = Gd. From the magnetization measurements, the R+3 magnetic moments in the Tb, Dy, and Ho compounds are found to have an easy-plane anisotropy, with the easy plane being the ab (RC) plane, whereas the Tm moments in the R = Tm compound are found to have an easy axis anisotropy with the easy axis along the c axis. The Er compound shows intermediate behavior. These anisotropies, together with the isotropy for R = Gd, are discussed and found to be in good agreement with point-charge CEF prediction. The intermediate anisotropy in R = Er compound is found to be due to the small value of Steven's coefficient B-2(0). (C) 1998 Elsevier Science B.V.