Effective field theory for the Ising model with a fluctuating exchange integral in an asymmetric bimodal random magnetic field: A differential operator technique

TL;DR

This paper develops an effective field theory using differential operators to analyze the phase transitions and magnetic properties of a disordered Ising model with fluctuating bonds and asymmetric bimodal random fields on a square lattice.

Contribution

It introduces a novel effective field approach incorporating fluctuating exchange interactions and asymmetric bimodal random fields in the Ising model.

Findings

Phase diagrams for various parameters are mapped out.

Transition temperatures are estimated under different disorder conditions.

Magnetization profiles are computed as functions of temperature and field strength.

Abstract

The spin-1/2 Ising model on a square lattice, with fluctuating bond interactions between nearest neighbors and in the presence of a random magnetic field, is investigated within the framework of the effective field theory based on the use of the differential operator relation. The random field is drawn from the asymmetric and anisotropic bimodal probability distribution $P(h_{i})=p \delta(h_{i}-h_{1}) + q \delta (h_{i}+ ch_{1})$, where the site probabilities $p,q$ take on values within the interval $[0,1]$ with the constraint $p+q=1$; $h_{i}$ is the random field variable with strength $h_{1}$ and $c$ the competition parameter, which is the ratio of the strength of the random magnetic field in the two principal directions $+z$ and $-z$; $c$ is considered to be positive resulting in competing random fields. The fluctuating bond is drawn from the symmetric but anisotropic bimodal probability distribution $P(J_{ij})=\frac{1}{2}\{\delta(J_{ij}-(J+\Delta)) + \delta (J_{ij}-(J-\Delta))\}$, where $J$ and $\Delta$ represent the average value and standard deviation of $J_{ij}$, respectively. We estimate the transition temperatures, phase diagrams (for various values of system's parameters $c,p,h_{1},\Delta$), susceptibility, equilibrium equation for magnetization, which is solved in order to determine the magnetization profile with respect to $T$ and $h_{1}$.