Polarization and magnetization properties of ferroelectric/ ferromagnetic layer films under external field
Authors: Zheng Wei , Du An ,   College of Sciences, Northeastern University, Shenyang 110819, China,   College of Physics Science Technology, Shenyang Normal University, Shenyang 110034, China
Published: December 2020

<sec>A ferroelectric/ferromagnetic bilayer film model is established. The electric moment of ferroelectric layer is described by continuous scalars, and the spins of ferromagnetic layer are described by classical vectors. The thermodynamic properties, polarization and magnetization behavior are simulated by using Monte Carlo method. The temperature dependence of internal energy, specific heat, polarization and magnetization of the system under zero field are given, and the polarization and magnetization behavior of the system under an external magnetic field and under an external electric field are studied respectively. </sec><sec>Simulation results show that the values of internal energy, specific heat, polarization and magnetization of the bilayer films under no action of external field are obviously different from each other due to the fact that their interlayer coupling coefficients are different. When the interfacial coupling is weak (<i>J</i><sub>em</sub> = 0.01), the bilayer films exhibit their own thermodynamic properties. The interaction between ferroelectric layer and ferromagnetic layer increases with the increase of interlayer coupling coefficient. When the interfacial coupling increases to a certain extent (<i>J</i><sub>em</sub> = 0.5), the bilayer film is coupled into a whole and exhibits a uniform thermodynamic behavior. The phase transition temperature of the system increases significantly.</sec><sec>In an external magnetic field, the ferromagnetic layer shows hysteresis behavior, and the ferroelectric layer also shows hysteresis behavior. At relatively low temperature (<i>T</i> = 0.08), the hysteresis loop of ferromagnetic layer and ferroelectric layer exhibit bias behavior, the area of hysteresis loop of ferroelectric layer is small when the interfacial coupling is weak. With the increase of interfacial coupling, the phenomenon of bias is more obvious, and the area of hysteresis loop of ferroelectric layer also increases significantly. When the interfacial coupling reaches <i>J</i><sub>em</sub> = 0.75, the polarization behavior of the ferroelectric layer fully responds to the magnetization behavior of the ferromagnetic layer, and neither the bias phenomenon of the ferromagnetic layer nor the bias phenomenon of the ferroelectric layer is still existent. As temperature increases (<i>T</i> = 0.4), the phenomenon of bias disappears even if the interlayer coupling is weak. In an external electric field, the hysteresis behavior of ferromagnetic layer and the hysteresis behavior of ferroelectric layer are similar to those in an external magnetic field. The difference is that the bias phenomenon of the bilayer film still exists for weak interfacial coupling at relatively high temperature (<i>T</i> = 0.4). The theoretical results are in good agreement with the experimental results reported in the literature.</sec>