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.
Mesoscopic phase separation in NaxCoO2 (0.65<=x<=0.75 ) / P. Carretta; M. Mariani; C. B. Azzoni; M. C. Mozzati; I. Bradaric; I Savic; A. Feher; J. Sebek. - In: PHYSICAL REVIEW. B, CONDENSED MATTER AND MATERIALS PHYSICS. - ISSN 1098-0121. - ELETTRONICO. - 70:(2004), pp. 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.