A Monte Carlo study on the variation of residual magnetisation with the ratio of coupling strengths and non-magnetic impurities in an Ising trilayer

Abstract

We have studied a spin-1/2, ABA Ising trilayer system with two different types of interactions, in-plane ferromagnetic and out-of-plane anti-ferromagnetic, among the lattice sites, on different layers. In the pure case, devoid of any impurity, we employed Monte-Carlo method with single spin-flip Metropolis algorithm to find out the anti-ferromagnetic critical temperature (Néel temperature) and another lower temperature, called the compensation temperature, both with total magnetisation zero, in accordance with already established results for square lattice. Then non-magnetic impurities (spin value = 0) were implanted on each layer at randomly picked sites and their concentration was increased in steps from 5% to 20%. The ratio of inter-planar anti-ferromagnetic to mid-layer ferromagnetic coupling strength as well as the ratio of top and bottom layer ferromagnetic to mid layer ferromagnetic coupling strength were also varied and Néel and compensation temperatures, both were observed shifting towards lower temperature values with increase in concentration of impurities in the lattice for any fixed ratio of different coupling strengths, in absence of any external magnetic field. In addition, the magnitude of the residual magnetisation i.e. the ratio of the peak value of the magnetisation in between Néel and compensation points and the saturated value of magnetisation, was also observed to vary with different values of controlling parameters.