Magnetic properties of Ruddlesden-Popper phases Sr$_{3-x}$Y$_{x}$(Fe$_{1.25}$Ni$_{0.75}$)O$_{7-\delta}$: A combined experimental and theoretical investigation

TL;DR

This study combines experimental and theoretical methods to analyze how Y substitution and oxygen content influence the magnetic properties of Sr$_{3-x}$Y$_{x}$(Fe$_{1.25}$Ni$_{0.75}$)O$_{7- delta}$, revealing increased Néel temperatures and antiferromagnetic order stabilization.

Contribution

It provides a comprehensive analysis of magnetic behavior in Ruddlesden-Popper phases using SQUID, neutron diffraction, and density functional theory, highlighting the role of inter-layer exchange interactions.

Findings

Néel temperature increases with Y content and oxygen occupancy.

All samples exhibit antiferromagnetic order at low temperatures.

3D magnetic order is stabilized by inter-layer exchange couplings.

Abstract

We present a comprehensive study of the magnetic properties of Sr$_{3-x}$Y$_{x}$(Fe$_{1.25}$Ni$_{0.75}$)O$_{7-\delta}$ ($0 \leq x \leq 0.75$). Experimentally, the magnetic properties are investigated using superconducting quantum interference device (SQUID) magnetometry and neutron powder diffraction (NPD). This is complemented by the theoretical study based on density functional theory as well as the Heisenberg exchange parameters. Experimental results show an increase in the N\'eel temperature ($T_N$) with the increase of Y concentrations and O occupancy. The NPD data reveals all samples are antiferromagnetically ordered at low temperatures, which has been confirmed by our theoretical simulations for the selected samples. Our first-principles calculations suggest that the 3D magnetic order is stabilized due to finite inter-layer exchange couplings. The latter give rise to a finite inter-layer spin correlations which disappear above the $T_N$.