Long-range antiferromagnetic ordering in Bi2CuO4.

Abstract

The results of an investigation of ${\mathrm{Bi}}_{2}$${\mathrm{CuO}}_{4}$ using x-ray and neutron powder diffraction, dc magnetometry, and electron-spin resonance are presented. Simultaneous refinement of the room-temperature x-ray and neutron-diffraction data was used to obtain accurate cell parameters and atomic positions. Neutron-diffraction data at 13 and 300 K show that the appropriate space group is P4/ncc at both temperatures and reveal the appearance at the lower temperature of two magnetic peaks, which can be indexed as (100) and (210) reflections. While they are clearly indicative of long-range antiferromagnetic order, on the basis of these powder data alone one cannot determine the moment direction. However, on the assumption that the moments lie along the c axis, the copper magnetic moment is (0.56\ifmmode\pm\else\textpm\fi{}0.04)${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$. dc magnetometry was performed at temperatures from 1.66 to 400 K and fields ranging from 0.5 to 50 kOe. The magnetization showed no field saturation even at 1.66 K and 45 kOe. The susceptibility showed a maximum near 50.4 K with a Curie tail observed at low temperatures. Antiferromagnetic interactions dominated at all temperatures. The magnetic behavior is like that of a three-dimensional antiferromagnetic system. ESR experiments were done over the temperature range 4.3--300 K. For temperatures above 50 K, one broad line with g=2.09 was observed. The resonance field shifted to higher values for T37 K, with an eventual splitting of the line below 15 K. These ESR signals can be associated with antiferromagnetic resonance modes, consistent with an ordered antiferromagnetic phase.