Magnetic-Properties of RSr2NbCu2O8; R = Nd, and Tb Compounds Prepared under Extreme Conditions

The niobio-cuprates with starting composition, RSr2Nb0.9Cu2.1O7.9; R = Nd, and Tb have been prepared under extreme synthesis conditions and characterized by powder X-ray diffraction technique and their magnetic properties were investigated briefly in this article. The present high-pressure synthesized NdSr2Nb0.9Cu2.1O7.9 (Nd/1212Nb) compound has been compared briefly with the reported ambient pressure prepared compound. X-ray diffraction patterns of RSr2Nb0.9Cu2.1O7.9; R = Nd, and Tb compounds taken at room temperature clearly indicate that the space group P4/mmm (123) is likely for the structure. Magnetic susceptibility, ( vs T) measurements on NdSr2Nb0.9Cu2.1O7.9 compound reveal likely (Pauli) paramagnetic-nature where as the magnetization versus field, M(H) data taken at low temperature (1.8 K) reveals non-linear increase of magnetization with respect to the applied magnetic field indicating possibly due to canted antiferromagnetic interaction in this Nd compound and a magnetic saturation is not seen, signifying no magnetic orders within the range. Although a comparable M(H) isotherm has been observed at selected temperatures for most of the highpressure synthesized niobio-cuprates, they show different results on magnetic susceptibilities, specific heat and transport measurements. Interestingly, unlike NdSr2Nb0.9Cu2.1O7.9 compound, the TbSr2Nb0.9Cu2.1O7.9 (Tb/1212Nb) compound (known for the first time) specifies two antiferromagnetic-like transitions (TN) at ~41 K as well as at ~ 8 K with branching of zero-field-cooled (zfc) and field-cooled (fc) magnetization and a zfc cusp like down turn in magnetization at ~8 K, followed by negative susceptibility at 2 K. The M(H) plot measured at 1.8 K and ±70 kOe conditions reveals abnormal (spin-flop) magnetization isotherm for Tb/1212Nb compound. The paramagnetic Weiss temperature, w and the paramagnetic effective moment, peff obtained from the linear region of (T) plots are: –64.07 K and 3.71 μB/Nd for Nd compound and –15.67 K and 9.42 μB/Tb for Tb compound, respectively. The negative sign of w ascertains the antiferromagnetic correlations in these studied compounds.