[Paper Review] Critical phenomena of nano phase evolution in a first order transition

Yongseong Choi, D. J. Keavney+6 more|arXiv (Cornell University)|May 16, 2014

Physics of Superconductivity and Magnetism19 references3 citations

TL;DR

This study investigates critical phenomena in nano-phase evolution during a first-order magneto-structural transition in FeRh. Using in situ X-ray diffraction and magnetometry, it reveals a novel intermediate phase at the interface between initial and final phases, characterized by suppressed spin order due to competing antiferromagnetic and ferromagnetic interactions, leading to a static mixed-phase morphology and critical behavior in the final phase's temperature evolution.

ABSTRACT

First order phase transitions occur discretely from one state to another, however they often display continuous behavior. To understand this nature, it is essential to probe how the emergent phase nucleates, interacts and evolves with the initial phase across the transition at microscopic scales. Here, the prototypical first-order magneto-structural transition in FeRh is used to investigate these phenomena. We find that the temperature evolution of the final phase exhibits critical behavior. Furthermore, a difference between the structure and magnetic transition temperatures reveals a novel intermediate phase created from the interface between the initial and nucleated final states. This emergent phase, characterized by its lack of spin order due to the competition between the antiferromagnetic and ferromagnetic interactions, leads to suppression of the dynamic aspect of the transition, generating a static mixed-phase-morphology. Understanding and controlling the transition process at this spatial scale is critical to optimizing functional device capabilities.

Motivation & Objective

• To understand the microscopic mechanisms governing phase nucleation and evolution in first-order transitions, which often exhibit continuous behavior despite discrete transitions.
• To resolve the discrepancy between structural and magnetic transition temperatures in FeRh, a prototypical first-order transition material.
• To identify and characterize emergent interfacial phases that influence the dynamics and morphology of the phase transition.
• To investigate how nanoscale phase coexistence and competing interactions affect the static versus dynamic nature of the transition.
• To provide insights into controlling phase evolution for optimizing functional device performance in materials with strong phase transitions.

Proposed method

• Employing in situ X-ray diffraction (XRD) to track structural evolution during the phase transition in FeRh across temperature gradients.
• Conducting in situ magnetometry to monitor magnetic transitions and correlate them with structural changes.
• Analyzing temperature-dependent XRD patterns to identify distinct phases and their interfacial structures.
• Using the observed differences between structural and magnetic transition temperatures to infer the existence of an intermediate phase.
• Applying critical scaling analysis to the temperature evolution of the final phase to assess critical behavior.
• Characterizing the interfacial region via diffraction peak broadening and asymmetry to infer the presence of a disordered, non-magnetic phase.

Experimental results

Research questions

• RQ1 How does the temperature evolution of the final phase in a first-order transition in FeRh exhibit critical behavior?
• RQ2 What causes the discrepancy between the structural and magnetic transition temperatures in FeRh?
• RQ3 What is the nature and origin of the intermediate phase formed at the interface between the initial and final phases?
• RQ4 How do competing antiferromagnetic and ferromagnetic interactions influence the magnetic order and dynamics at the interface?
• RQ5 What is the impact of the emergent phase on the overall phase morphology and transition kinetics?

Key findings

• The temperature evolution of the final phase in FeRh exhibits critical behavior, indicating a continuous-like transition despite the first-order nature of the overall process.
• A distinct intermediate phase forms at the interface between the initial and final phases, evidenced by a separation between structural and magnetic transition temperatures.
• This intermediate phase lacks long-range spin order due to the competition between antiferromagnetic and ferromagnetic interactions.
• The suppression of dynamic fluctuations in the transition leads to a static mixed-phase morphology, stabilizing the interface.
• The interfacial region exhibits unique diffraction signatures, including peak broadening and asymmetry, consistent with a disordered, non-magnetic phase.
• The findings suggest that nanoscale phase evolution is governed by interfacial critical phenomena, which must be controlled for functional device applications.