Contrasted role of disorder for magnetic properties in an original mixed valency iron Phosphate

TL;DR

This study investigates the magnetic properties of a unique mixed valency iron phosphate with a novel structure, revealing how disorder influences magnetic behavior and long-range order.

Contribution

It introduces a new mixed valency iron phosphate structure and analyzes how disorder affects its magnetic properties and phase transitions.

Findings

Disorder induces spin-glass-like behavior.

Long-range magnetic order remains unaffected by small-scale disorder.

Low-temperature magnetization decreases and shows irreversible metamagnetic transition.

Abstract

We have measured the magnetic properties of a mixed valency iron phosphate. It presents an original structure with crossed chains containing Fe II and orthogonal to the longest direction of the crystallites. Microstructural investigations using electron microscopy show the presence of random nano-twinning. The ac susceptibility measurements demonstrate similarities with the kinetics of a disordered magnetic, spin-glass like, state but are shown to be essentially due to this peculiar disorder. Scaling properties are characteristics of 3D second order transition implying that this disorder at a small scale does not influence significantly long range magnetic ordering. At low temperature, a decrease of the spontaneous magnetization and an irreversible metamagnetic transition is observed, and is attributed to a canting of the spins in the iron chain.