The effect of Al doping on the structure and magnetism in cobaltite CaBaCo4O7

TL;DR

This study investigates how aluminum doping affects the structural and magnetic properties of CaBaCo4O7, revealing a transition from orthorhombic to hexagonal symmetry and a suppression of ferrimagnetism leading to a spin-glass state.

Contribution

It provides new insights into the effects of Al doping on the structure and magnetism of CaBaCo4O7, highlighting the decoupling of lattice and spin degrees of freedom.

Findings

Structural transition from orthorhombic to hexagonal at x > 0.1

Decrease in Curie temperature and magnetization with Al doping

Suppression of short-range magnetic correlations at high Al content

Abstract

We report the effects of Al-doping on the structure and magnetic properties in CaBa(Co$_{1-x}$Al$_{x}$)$_4$O$_7$ (0$\leq$x$\leq$0.25). The system exhibits a structural transition from an orthorhombic symmetry to a hexagonal symmetry when the Al content exceeds $x =$ 0.1. The Curie temperature and the value of the magnetization decrease with increasing Al doping level, indicating that the ferrimagnetic ground state is gradually suppressed. The ground state eventually transits into a spin-glass state for $x >$ 0.1. Moreover, the short-range magnetic correlations, which occur at high temperatures in CaBaCo$_4$O$_7$, are found to be gradually suppressed with increasing Al content and eventually disappear for $x =$ 0.25. By comparing our results with other Co-site doping cases, we suggest that the lattice and the spin degrees of freedom are relatively decoupled in CaBaCo$_4$O$_7$.