Predictive Indicator of Critical Point in Equilibrium and Nonequilibrium Magnetic Systems

TL;DR

This paper introduces a unified method using static and dynamic response functions to predict critical points in both equilibrium and nonequilibrium magnetic systems, improving early detection and reducing costs.

Contribution

It develops a novel, unified predictive indicator framework based on response functions applicable to diverse magnetic phase transitions.

Findings

Static response diverges at equilibrium critical points.

Dynamic response at resonance diverges at nonequilibrium critical points.

Indicators are noise-resilient and applicable to both transition types.

Abstract

Determining critical points of phase transitions from partial data is essential to avoid abrupt system collapses and reducing experimental or computational costs. However, the complex physical systems and phase transition phenomena have long hindered the development of unified approaches applicable to both equilibrium and nonequilibrium phase transitions. In this work, we propose predictive indicators to determine critical points in equilibrium and nonequilibrium magnetic systems based on frequency-dependent response function. For equilibrium phase transition, such as magnetization switching under magnetic field, the static magnetization response function to a perturbing magnetic field diverges at the critical field, serving as a noise-resilient predictive indicator that also reflects the transition order and critical exponents. In contrast, for nonequilibrium phase transition, such as magnetization switching driven by spin-transfer torque, static response fails to signal criticality. Instead, the dynamic response at ferromagnetic resonance frequency diverges at the critical point, which is also robust against thermal noise. We further demonstrate that these static and dynamic indicators can be unified in the frame of first-order linear differential systems, offering a generalizable strategy for predicting criticality in both equilibrium and nonequilibrium transitions.