Magnetic and Metal-Insulator Transitions in beta-Na0.5CoO2 and gamma-K0.5CoO2 -NMR and Neutron Diffraction Studies-

TL;DR

This study investigates magnetic and metal-insulator transitions in beta-Na0.5CoO2 and gamma-K0.5CoO2 using NMR and neutron diffraction, revealing phase transitions, antiferromagnetic order, and effects of layer stacking and interlayer distance.

Contribution

It provides new insights into the phase transitions and magnetic properties of beta-Na0.5CoO2 and gamma-K0.5CoO2, highlighting the role of layer stacking and interlayer distance.

Findings

Successive phase transitions at Tc1 and Tc2 in both systems.

Antiferromagnetic order exists below Tc1 in both compounds.

Differences in physical quantities linked to interlayer spacing.

Abstract

Co-oxides beta-Na0.5CoO2 and gamma-K0.5CoO2 have been prepared by the Na de-intercalation from alpha-NaCoO2 and by the floating-zone method, respectively. It has been found that successive phase transitions take place at temperatures Tc1 and Tc2 in both systems. The appearance of the internal magnetic field at Tc1 with decreasing temperature T indicates that the antiferromagnetic order exists at T < Tc1, as in gamma-Na0.5CoO2. For beta-Na0.5CoO2, the transition temperatures and the NMR parameters determined from the data taken for magnetically ordered state are similar to those of gamma-Na0.5CoO2, indicating that the difference of the stacking ways of the CoO2 layers between these systems do not significantly affect their physical properties. For gamma-K0.5CoO2, the quantitative difference of the physical quantities are found from those of beta- and gamma-Na0.5CoO2. The difference between the values of Tci (i = 1 and 2) of these systems might be explained by considering the distance between CoO2 layers.