Magnetism in four-layered Aurivillius Bi$_5$FeTi$_3$O$_{15}$ at high pressures : A nuclear forward scattering study

TL;DR

This study investigates the structural and magnetic behavior of four-layer Aurivillius Bi$_5$FeTi$_3$O$_{15}$ under high pressure, revealing pressure-induced structural modifications and pressure-enhanced magnetic ordering at low temperatures.

Contribution

It provides new insights into how high pressure influences the structure and magnetism of BFTO, including the emergence of magnetic order at 5K under pressure.

Findings

Structural modifications occur at different pressures without clear phase transitions.

Magnetic ordering develops at 5K under high pressure.

Magnetism diminishes at higher temperatures, disappearing above 20K.

Abstract

We report the structural and magnetic properties of four-layer Aurivillius compound Bi$_5$FeTi$_3$O$_{15}$ (BFTO) at high hydrostatic pressure conditions. The high-pressure XRD data does not explicitly show structural phase transitions with hydrostatic pressure, however the observed changes in lattice parameters indicate structural modifications at different pressure values. In the initial pressure region values, the lattice parameters $\textit{a}$- and $\textit{b}$- are nearly equal implying a quasi-tetragonal structure, however as the pressure increases $\textit{a}$- and $\textit{b}$- diverges apart and exhibits complete orthorhombic phase at pressure values of about $\geq$8 GPa. Principal component analysis of high pressure Raman measurements point out an evident change in the local structure at about 5.5 GPa indicating that the evolution of the local structure under applied pressure seems to not follow crystallographic changes (long range order). Nuclear forward scattering (NFS) measurement reveal the development of magnetic ordering in BFTO at 5K with high pressures. A progressive increase in magnetic order is observed with increase in pressure at 5K. Further, NFS measurements carried out at constant pressure (6.4GPa) and different temperatures indicate that the developed magnetism disappears at higher temperatures (20K). It is attempted to explain these observations in terms of the observed structural parameter variation with pressure.