Magnetic order and spin dynamics in the helical magnetic system Fe$_3$PO$_4$O$_3$

TL;DR

This study investigates the magnetic order and spin dynamics in Fe₃PO₄O₃ using muon spin rotation and Mössbauer spectroscopy, revealing a helical magnetic structure and complex low-temperature magnetic behavior.

Contribution

The paper provides detailed experimental evidence for the helical magnetic structure and dynamic spin behavior in Fe₃PO₄O₃, expanding understanding of its magnetic properties.

Findings

Confirmation of static long-range magnetic order below 164 K

Evidence of a helical magnetic structure from μSR data

Detection of a secondary magnetic fluctuation peak at 35 K

Abstract

The 3$d$-electronic spin dynamics and the magnetic order in Fe$_3$PO$_4$O$_3$ were investigated by muon spin rotation and relaxation ($\mu$SR) and $^{57}$Fe M\"ossbauer spectroscopy. Zero-field (ZF)-$\mu$SR and $^{57}$Fe M\"ossbauer studies confirm static long range magnetic ordering below $T_{\mathrm{N}}$ $\approx$ 164\,K. Both transverse-field (TF) and ZF-$\mu$SR results evidence 100\% magnetic volume fraction in the ordered state. The ZF-$\mu$SR time spectra can be best described by a Bessel function, which is consistent with the helical magnetic structure proposed by neutron scattering experiments. The M\"ossbauer spectra are described in detail by considering the specific angular distribution of the local hyperfine field $B_{\mathrm{hyp}}$ with respect to the local electric field gradient. The $\mu$SR spin-lattice relaxation rate exhibits two peaks: One at the magnetic ordering temperature related to critical magnetic fluctuations and another peak at 35\,K signaling the presence of a secondary low energy scale in Fe$_3$PO$_4$O$_3$.