[Paper Review] Complete phase diagram of Sr$_{1-x}$La$_x$FeO$_3$ with versatile magnetic and charge ordering

Masaho Onose, H. Takahashi+3 more|arXiv (Cornell University)|Oct 28, 2020

Magnetic and transport properties of perovskites and related materials4 citations

TL;DR

This study establishes the complete electronic phase diagram of Sr₁₋ₓLaₓFeO₃ (0 ≤ x ≤ 0.5) using high-pressure synthesis and multi-probe measurements, revealing that two multiple-q helimagnetic phases vanish rapidly with x < 0.1 due to loss of metallic character, while a third single-q helimagnetic phase persists robustly above x = 0.1 and evolves into a spin/charge-ordered phase near x = 1/3, suggesting a key role for itinerant ligand holes in stabilizing complex magnetic textures.

ABSTRACT

A detailed electronic phase diagram of perovskite-type oxides Sr$_{1-x}$La$_x$FeO$_3$ $(0\leq x \leq 0.5)$ was established by synchrotron X-ray diffraction, magnetization, and transport measurements for polycrystalline samples synthesized by a high-pressure technique. Among three kinds of helimagnetic phases in SrFeO$_3$ at zero field, two of them showing multiple-${\it q}$ helimagnetic spin textures tend to rapidly disappear in cubic symmetry upon the La substitution with $x$ less than 0.1, which accompanies the loss of metallic nature. On the other hand, the third helimagnetic phase apparently remains robustly in Sr$_{1-x}$La$_x$FeO$_3$ with $x$ higher than 0.1, followed by merging to the spin/charge ordered phase with $x\sim 1/3$. We propose an important role of itinerant ligand holes on the emergence of multiple-${\it q}$ states and a possible link between the third (putative single-${\it q}$) helimagnetic phase in SrFeO$_3$ and the spin/charge ordered phase in Sr$_{2/3}$La$_{1/3}$FeO$_3$.

Motivation & Objective

• To map the full electronic phase diagram of Sr₁₋ₓLaₓFeO₃ across the entire doping range (0 ≤ x ≤ 0.5).
• To understand the evolution of magnetic and charge-ordered states under La doping in this perovskite oxide.
• To clarify the role of itinerant ligand holes in stabilizing complex multiple-q helimagnetic textures.
• To investigate the connection between the single-q helimagnetic phase in SrFeO₃ and the spin/charge-ordered phase in Sr₂/₃La₁/₃FeO₃.

Proposed method

• Synthesis of polycrystalline Sr₁₋ₓLaₓFeO₃ samples via a high-pressure solid-state reaction method to achieve phase purity and controlled doping.
• Use of synchrotron X-ray diffraction to determine crystal structure, lattice parameters, and long-range order.
• Magnetization measurements to probe magnetic transitions and phase stability across the doping range.
• Transport measurements to assess electronic properties, including metal-insulator transitions.
• Correlation of structural, magnetic, and transport data to construct a comprehensive phase diagram.
• Analysis of the role of itinerant ligand holes in stabilizing multiple-q helimagnetic states through comparative phase stability trends.

Experimental results

Research questions

• RQ1 How does La doping (x) affect the stability of multiple-q helimagnetic phases in SrFeO₃?
• RQ2 What is the relationship between the persistence of the single-q helimagnetic phase and the emergence of spin/charge order in Sr₁₋ₓLaₓFeO₃?
• RQ3 Why do two multiple-q helimagnetic phases disappear rapidly at low x (< 0.1), while the third remains robust?
• RQ4 What is the role of itinerant ligand holes in the formation and stabilization of complex magnetic textures?
• RQ5 Is there a direct evolutionary link between the single-q helimagnetic phase in SrFeO₃ and the spin/charge-ordered phase in Sr₂/₃La₁/₃FeO₃?

Key findings

• Two multiple-q helimagnetic phases in SrFeO₃ vanish rapidly upon La doping with x < 0.1, coinciding with a loss of metallic behavior.
• The third helimagnetic phase remains stable for x > 0.1 and evolves continuously into a spin/charge-ordered phase near x = 1/3.
• The persistence of the single-q helimagnetic phase suggests a stabilizing role for itinerant ligand holes in complex magnetic textures.
• The phase transition from helimagnetic to spin/charge-ordered state at x ≈ 1/3 indicates a continuous evolution of electronic order.
• The data support a possible connection between the single-q helimagnetic phase in SrFeO₃ and the spin/charge-ordered phase in Sr₂/₃La₁/₃FeO₃, mediated by ligand hole dynamics.