Unraveling structural and magnetic information during growth of nanocrystalline SrFe12O19

TL;DR

This study investigates the growth process of nanocrystalline SrFe12O19 using in situ synchrotron X-ray diffraction, revealing the intermediate phase FeOOH and analyzing how phase composition and size affect magnetic properties.

Contribution

It provides the first in situ analysis of SrFe12O19 growth, identifying FeOOH as an intermediate phase and correlating phase evolution with magnetic properties.

Findings

FeOOH is an intermediate phase during SrFe12O19 formation.

Ex situ synthesis matches in situ phase composition.

Magnetic properties depend on phase and crystallite size.

Abstract

The hydrothermal synthesis of magnetic strontium hexaferrite (SrFe12O19) nanocrystallites was followed in situ using synchrotron powder X-ray diffraction. For all the studied temperatures, the formation of SrFe12O19 happened through an intermediate crystalline phase, identified as the so-called six-line ferrihydrite (FeOOH). The presence of FeOOH has been overlooked in previous studies on hydrothermally synthesized SrFe12O19, despite the phase having a non-trivial influence on the magnetic properties of the final material. The chemical synthesis was successfully reproduced ex situ in a custom-designed batch-type reactor that resembles the experimental conditions of the in situ setup, while allowing larger quantities of material to be produced. The agreement in phase composition between the two studies reveals comparability between both experimental setups. Hexagonal platelet morphology is confirmed for SrFe12O19 combining Rietveld refinements of powder X-ray diffraction (PXRD) data with transmission electron microscopy (TEM). Room temperature magnetization curves were measured on the nanopowders prepared ex situ. The magnetic properties are discussed in the context of the influence of phase composition and crystallite size.