Long-range magnetic ordering and structural phase transition in disordered high-entropy spinel chromites

TL;DR

This study investigates the magnetic and structural phase transitions in disordered high-entropy spinel chromites, revealing long-range magnetic order and entropy-driven structural stabilization despite chemical disorder.

Contribution

It provides the first systematic analysis of temperature-dependent magnetic and structural transitions in Cr-based high-entropy spinels, highlighting entropy's role in stabilizing order.

Findings

Both systems crystallize in cubic structure at room temperature.

Antiferromagnetic order emerges below 49 K and 35 K.

Structural transition from cubic to orthorhombic symmetry occurs around 55 K and 85 K.

Abstract

High-entropy spinel oxides provide an excellent platform for investigating entropy-stabilized correlated systems with strong configurational disorder. In this work, we systematically study the temperature evolution of the structural and magnetic properties of Cr-based high-entropy spinels with compositions $(Mn_{0.2}Co_{0.2}Ni_{0.2}Cu_{0.2}Zn_{0.2})Cr_2O_4$ and $(Mg_{0.2}Co_{0.2}Ni_{0.2}Cu_{0.2}Zn_{0.2})Cr_2O_4$. Our results reveal that both systems crystallize in cubic structure with space group \textit{$Fd\overline{3}m$} at room temperature. Each system undergoes antiferromagnetic ordering below the N\'eel temperatures $ T_N$ = 49 K and 35 K, respectively. Neutron diffraction measurements confirm the emergence of long-range magnetic order with spiral spin arrangement. Both systems exhibit a structural phase transition from cubic \textit{$Fd\overline{3}m$} to orthorhombic \textit{Fddd} symmetry at approximately 55 K and 85 K, respectively. Notably, despite the significant chemical disorder at the A site, both systems undergo transitions analogous to those observed in low entropy spinel systems. This behavior suggests that high configurational entropy may promote global structural stabilization despite local chemical disorder, thereby preserving long-range orderings and the characteristic symmetry-breaking transitions of the pristine spinel systems.