Pseudotransitions in a dilute Ising chain

TL;DR

This paper analyzes a one-dimensional dilute magnetic chain, revealing pseudotransitions between magnetic and charge orders, characterized by features similar to phase transitions, and explores their connection to phase separation and thermodynamic behavior.

Contribution

It introduces an exact transfer-matrix method to study pseudotransitions in a dilute Ising chain and links these phenomena to phase separation into different ordered regions.

Findings

Pseudotransitions occur only between simple charge and magnetic quasiorders.

Second-order pseudotransitions are observed in the dilute case.

Thermodynamic features resemble first- and second-order phase transitions.

Abstract

This study provides a comprehensive analysis of the ground state and thermodynamic properties of a spin-pseudospin chain representing a model of a one-dimensional dilute magnet with two types of nonmagnetic charged impurities. For this purpose, a method utilizing the transfer-matrix properties is employed. Despite the wide variety of intriguing frustrated phase states, we show that the model showcases pseudotransitions solely between simple charge and magnetic quasiorders. These pseudotransitions are characterized by distinct features in the thermodynamic and magnetic quantities, resembling first- and second-order phase transitions. In addition to pseudotransitions for the ``pure'' system, similar to those observed in other one-dimensional spin models, this study also reveals the presence of ``second-order'' pseudotransitions for the dilute case. We show that the nature of these discovered pseudotransitions is associated with the phase separation in the chain into regions of (anti)ferromagnetic and charge-ordered phases. The ability to compare the results of an exact transfer-matrix calculation with a simple phenomenological description within the framework of Maxwell construction contributes to a deeper understanding of both the physical mechanisms underlying this phenomenon and the analytical methods used.