Neutron diffraction analysis of magnetic ordering in YSr2Cu2RuO8

摘要

The superconducting ruthenocuprates RESr2Cu2RuO8 (where RE is a rare earth or Y) have been interpreted as ferromagnetic superconductors, based on a strong response to applied field at the Ru Neel temperature (around 130 K). However, neutron diffraction measurements on the Gd compound by Lynn Phys. Rev. B 61, 1214964 (2000) (using a separated isotope) show evidence only of antiferromagnetic order, while very limited data by Takagiwa J. Phys. Soc. Jpn. 70, 333 (2001) on the Y compound show one antiferromagnetic Bragg peak and possible coexisting ferromagnetism. We have studied a sample of YSr2Cu2.1Ru0.9O7.9 prepared by a high pressure-high temperature route. Temperature dependent neutron powder diffraction shows antiferromagnetic order, manifested by the observation of the 1/2, 1/2, 1/2 and 1/2, 1/2, 3/2 reflections, which appear at 135 K as suggested by the superconducting quantum interference device (SQUID) data. Their intensities at the lowest temperature are consistent with a c-axis orientation of the Ru magnetic moments. Although the lowest order nuclear Bragg peak shows a small intensity increase as the temperature is lowered, this is attributed to magnetic ordering of the Cu planes and not to the presence of a ferromagnetic component, in agreement with the polarized neutron data of Lynn Phys. Rev. B. 61, 1214964 (2000) Magnetic resonance and SQUID data on the same sample (to be reported elsewhere) show a complex picture, associated with Cu magnetic ordering.