NMR studies of successive transition in Na0.5CoO2

• Published in: Journal of magnetism and magnetic materials Vol. 310; no. 2; pp. 675 - 677
• Main Authors: KOBAYASHI, Y, YOKOI, M, MOYOSHI, T, WATANABE, H, SATO, M
• Format: Conference Proceeding Journal Article
• Language: English
• Published: Amsterdam Elsevier Science 01.03.2007
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Exact sciences and technology; Magnetic phase boundaries (including magnetic transitions, metamagnetism, etc.); Magnetic properties and materials; Magnetic resonances and relaxations in condensed matter, mössbauer effect; Magnetically ordered materials: other intrinsic properties; Nuclear magnetic resonance and relaxation; Physics; Antiferromagnetism; 71.30. + h; 75.50.Ee; 76.60.-k; Na0.5CoO2i Antiferromagnet; Co NMR; Na NMR; Neutron diffraction; Na03CoO2; Zero field splitting; Sodium oxides; Magnetization; Neutron diffraction; Antiferromagnetic materials; Magnetic moments; Cobalt oxides; 1.3H2O; Phase separation; Nuclear quadrupole resonance; Anomaly; Nuclear magnetic resonance; Magnetic properties
• ISSN: 0304-8853
• DOI: 10.1016/j.jmmm.2006.10.175

To investigate the electric or magnetic characteristics of NaxCoO2, the parent system of the superconductor Na0.3CoO2*1.3H2O, the successive phase transition observed in Na0.5CoO2 at 87K (Tc1) and 53K (Tc2) have been studied by the means of NMR/NQR and neutron diffraction. The Co ions at one of the two crystallographically distinct Co sites with the lager nuQ value have the larger magnetic moments. They align antiferromagnetically at Tc1 with their direction within the CoO2 plane, while those at the other Co sites with the smaller nuQ value have the smaller moments. They align along the direction parallel to the c-axis. The ordered moments at these two distinct sites exhibit the same T dependences, indicating that the existence of these sites is not due to a macroscopic phase separation. Although we have observed the splitting of the zero-field NMR signals from the Co sites with the smaller nuQ value at Tc2, any other anomaly of the ordered magnetization has not been observed there in the T dependences of the neutron and NMR data. We also present results of 23Na-NMR studies of Na0.5CoO2.