Low Dimensional Magnetism in the High T c Superconductor LnBa 2 Cu 3 O 7-y (Ln=Nd, Sm, Gd, Ho, Er)

Heat capacities have been measured for the high T c superconductors LnBa 2 Cu 3 O 7-y (Ln=Y, Nd, Sm, Gd, Ho, Er) between 0.4K and 100K. A cooperative heat capacity peak has been found at T m =0.585K for SmBa 2 Cu 3 O 7-y , 2.21K for GdBa 2 Cu 3 O 7-y and 0.60K for ErBa 2 Cu 3 O 7-y . In addition, broad heat capacity anomalies are found between 1K and 5K for all the compounds of magnetic rare earths studied. A semiquantitative fit can be obtained assuming that there exist two nearly independent systems of rare earth ions in LnBa 2 Cu 3 O 7-y , namely, a 2–d Ising system which is responsible for the sharp heat capacity peak and a 1–d Ising system which causes the rounded maximum.