Nuclear magnetic resonace (NMR), EPR and magnetization measurements in NaxCoO2 for 0.65<=x<=0.75 are presented. While the EPR signal arises from Co4+ magnetic moments ordering at Tc=26 K, 59Co NMR signal originates from cobalt nuclei in metallic regions with no long range magnetic order and characterized by a generalized susceptibility typical of strongly correlated metallic systems. This phase separation in metallic and magnetic insulating regions is argued to occur below T*(x) (220–270 K). Above T* an anomalous decrease in the intensity of the EPR signal is observed and associated with the delocalization of the electrons which for T<T* were localized on Co4+ d_(z)^2 orbitals. It is pointed out that the in-plane antiferromagnetic coupling J<<T* cannot be the driving force for the phase separation.
P. Carretta, M. Mariani, C. B. Azzoni, M. C. Mozzati, I. Bradaric, I Savic, et al. (2004). Mesoscopic phase separation in NaxCoO2 (0.65<=x<=0.75 ). PHYSICAL REVIEW. B, CONDENSED MATTER AND MATERIALS PHYSICS, 70, 1-9 [10.1103/PhysRevB.70.024409].
Mesoscopic phase separation in NaxCoO2 (0.65<=x<=0.75 )
MARIANI, MANUEL;
2004
Abstract
Nuclear magnetic resonace (NMR), EPR and magnetization measurements in NaxCoO2 for 0.65<=x<=0.75 are presented. While the EPR signal arises from Co4+ magnetic moments ordering at Tc=26 K, 59Co NMR signal originates from cobalt nuclei in metallic regions with no long range magnetic order and characterized by a generalized susceptibility typical of strongly correlated metallic systems. This phase separation in metallic and magnetic insulating regions is argued to occur below T*(x) (220–270 K). Above T* an anomalous decrease in the intensity of the EPR signal is observed and associated with the delocalization of the electrons which for TI documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
