RARE-EARTH MAGNETIC-ORDERING IN THE R2CUO4 CUPRATES (R = TB, DY, HO, ER AND TM)

Low-temperature AC magnetic susceptibility measurements on the heavy rare-earth antiferromapetic cuprates R2CuO4 which have a T' Nd2CuO4-like crystal structure are reported. A single susceptibility maximum is observed in all the compounds at different temperatures ranging from 1.5 K to 10 K, which is interpreted as indicative of antiferromagnetic long-range ordering of the rare-earth ions. No double peak structure is observed in any of these weak ferromagnetic compounds, at variance with the weak ferromagnetic compound Gd2CuO4 for which a second sudden transition, of uncertain origin, has been previously observed at T(L) almost-equal-to 20 K. The overall dependance of the antiferromagnetic ordering temperature on the single ion rare-earth magnetic moments do not follow a simple scaling with the De Gennes factor but rather a scaling with the full rare-earth magnetic moments, suggesting a pseudo-dipolar origin for the leading magnetic interaction coupling the rare-earth ions. Some important deviations are observed, however, which may be indicative of strong crystal field effects. It is suggested that the Suhl-Nakamura mechanism may ba a relevant mechanism to understand the rare-earth magnetic ordering in the R2CuO4 series (R = Nd- Tm).