Monte Carlo Study Of Dieletric Properties Of The Antiferroelectric/Ferroelectric Nano Bilayer

In recent years,various ferroelectric thin films have been prepared successfully with excellent physical and chemical properties.As an excellent functional material,antiferroelectric/ferroelectric thin film has attracted wide attention due to its important characteristics of high electric coefficient,ferroelectric,pyroelectric and piezoelectric.Its ferroelectric property can be reflected by spontaneous polarization,electric domain structure,blocking temperature(Curie temperature),electric hysteresis loop and so on.So it has practical application value and important significance in theory and experiment to study and explore the micro-mechanism of ferroelectric thin films.In this paper,the Monte Carlo simulation method was used to study the electrical and thermodynamic properties of antiferroelectric/ferroelectric mixed pseudo-spin Ising bilayer that composed of top layer spin-5/2 and bottom layer spin-2.In this paper,the effects of crystal field,exchange coupling,external electric field and temperature on the polarization,dielectric susceptibility,internal energy,specific heat and blocking temperature of antiferroelectric/ferroelectric bilayer are studied in detail.The phase diagram of the blocking temperature of the system under the influence of various physical parameters is obtained through analysis.The results show that the polarization P curves of the system are more abundant under the action of crystal field D2,which indicates that the influence of D2 on P is stronger than that of D1.When the crystal field and exchange coupling is changed,the total polarization curve of the system increases first and then decreases with the increase of temperature,and it presents a variety of saturation values of the polarization.These abundant P curves are also derived from the competition between crystal field and temperature.The results show that decreasing the crystal field or increasing the exchange coupling J1,|J3| and the external electric field E can improve blocking temperature TB and reduce the internal energy U,indicating that the system becomes more stable.The effects of different physical parameters on the polarization plateaus and the hysteresis behavior of antiferroelectric/ferroelectric bilayer are also discussed.The results show that the crystal field,exchange coupling and temperature have important effects on the low temperature electric property and the multi-loop hysteresis loops of the system.In the stronger crystal field,the spins of sublattices are more inclined to keep the state of low spin for a long time,and the strong crystal field leads to the existence of more polarization plateaus in the system,indicating that the system has more spin configurations at low temperature.And it is found that under the effects of crystal field and exchange coupling,the hysteresis behaviors of double loops,quadruple loops,decuple loops and twelve-fold loops may appear in the system,the increase in the number of hysteresis loops is due to the competition between the antiferroelectric exchange coupling and the external electric field.The increase of exchange coupling will make the area of the loops to increase obviously.