Antiferromagnetic ordering in superconducting and oxygen-deficient nonsuperconducting RBa2Cu3O7−δ compounds (R=Nd and Sm)

Abstract

Low-temperature (0.5–4 K) specific-heat measurements have been made on oxygen-deficient (δ≊0.5) nonsuperconducting RBa2Cu3O7−δ (R=Nd and Sm) compounds and compared to measurements previously performed on their high-critical-temperature Tc≊92 K superconducting counterparts (δ≊0.1). We show that the specific-heat anomaly due to magnetic ordering of the Nd3+ and Sm3+ ions in the Tc≊92 K superconducting RBa2Cu3O7−δ (R=Nd and Sm) compounds can be well described by a two-dimensional anisotropic antiferromagnetic Ising model with exchange-interaction parameters E1 and E2 in the a-b plane; the respective values of the Néel temperature TN and the ratio E1/E2 are 0.5 K and 50 for Nd and 0.61 K and 11 for Sm. The specific-heat anomaly of the oxygen-deficient nonsuperconducting NdBa2Cu3O7−δ compound is also associated with an antiferromagnetic transition according to low-temperature magnetization measurements, although the temperature dependence of the anomaly and the value of TN (∼1.7 K) are quite different from those in the superconducting state. Neutron-diffraction measurements on the Tc≊92 K superconducting phase of NdBa2Cu3O7−δ reveal that the Nd3+ magnetic moments form a simple antiferromagnetic structure in which the nearest-neighbor moments in all three dimensions are aligned antiparallel to one another along the c axis. In the Tc≊92 K superconducting phase, the ordered moment of the Nd3+ ions obtained from the neutron scattering data is 〈μz〉=(1.07±0.07)μB. The low-temperature specific-heat anomaly of the oxygen-deficient nonsuperconducting SmBa2Cu3O7−δ compound can be formally described by a Schottky anomaly for two doublets split by the crystalline electric field or a one-dimensional Ising model.

Source-reported materials — not catalogue approval

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