Transport (Electrical Resistivity/Magnetoresistance) and Specific Heat Measurements of Cu2 LnNbO8Sr2 with Ln = Er, Dy

The magnetic, transport and specific heat measurements of 1212-type compounds crystallized in tetragonal symmetry with starting composition, Cu-2.1 LnNb(0.9)O(7.9)Sr(2); Ln = Er, Dy have been investigated. The Cu-2.1 LnNb(0.9)O(7.9)Sr(2); Ln = Er, Dy compounds showed non-superconducting properties down to 1.8 K in the magnetic susceptibility measurements. The magnetic parameter (mu (eff)) obtained from the linear region of inverse molar magnetic susceptibility curves agrees with the calculated values for the respective free trivalent Er and Dy ions in Cu-2.1 LnNb(0.9)O(7.9)Sr(2); Ln = Er, Dy compounds. Though there is no strong evidence of magnetic ordering seen from magnetic susceptibilities, the hysteresis, M(H) curve obtained at 1.8 K looks like a canted antiferromagnet. The S-shaped (slightly curved) magnetization curve suggests weak ferromagnetic interactions that exist in the Ln = Er compound. A small hysteresis is observed with the coercive field (H (c)) of 49 Oe and the remnant magnetization (M (r)) of about 0.06 mu (B)/f.u. for Ln = Er. Interestingly, such a hysteresis loop opening is not seen for the Ln = Dy compound. While specific heat anomaly (lambda-like transition) was observed for Ln = Dy compound at low temperature (around 6 K), for Ln = Er compound such an anomaly was not seen in the specific heat measurements. The electrical resistivity versus temperature, rho(T), data showed that the compounds Cu-2.1 LnNb(0.9)O(7.9)Sr(2); Ln = Er, Dy are not in metallic state and they are really semiconducting-in-nature. Interestingly, rather large magnetoresistance, MR (similar to 18%) was observed at low temperature similar to 2 K for Er-based niobio-cuprate.