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Effect of next nearest neighbor interaction on thermodynamic properties of ultrathin magnetic films

This work studies on the thermodynamic properties of the ultra-thin magnetic films within the framework of a transverse Ising model. Equations for free energy, entropy and specific heat of spin system are obtained by using the mean field approximation. | VNU Journal of Science: Mathematics – Physics, Vol. 35, No. 1 (2019) 76-82 Original article Effect of Next Nearest Neighbor Interaction on Thermodynamic Properties of Ultrathin Magnetic Films Nguyen Tu Niem*, Bach Thanh Cong Faculty of Physics, VNU University of Science, 334 Nguyen Trai, Thanh Xuan Hanoi, Vietnam Received 15 January 2019 Revised 07 March 2019; Accepted 15 March 2019 Abstract: This work studies on the thermodynamic properties of the ultra-thin magnetic films within the framework of a transverse Ising model. Equations for free energy, entropy and specific heat of spin system are obtained by using the mean field approximation. We also analyze the effect of the next nearest neighbor interaction on critical temperature, layer magnetization and specific heat of the thin films. Keywords: Magnetic ultra-thin films, transverse Ising model, next nearest neighbor interaction, critical temperature. 1. Introduction Recently the ultra-thin magnetic films have been used more and more in memory and microwave devices. Many researches on the magnetic ultra-thin films have been carried out both experimentally and theoretically [1, 2]. The magnetic ultra-thin films have magnetic properties which are different from those of the bulk [3, 4]. Several models have been used to investigate the features of the films such as: Heisenberg model, transverse Ising model, XY model Among them, the transverse Ising model (TIM) is often used because its simplicity and usefulness. There are many works has applied TIM to investigate magnetic thin films within the framework of the mean field theory and effective field theory [4-7]. In a previous work [8], we investigated the dependence of the order-disorder phase transition temperature on the transversal field and obtained the explicit equation for this temperature. However, we only consider the nearest- neighbor (n.n) exchange interaction between spins in [8]. In the real magnetic ultrathin films, the next nearest- neighbor .