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The heterostructures formed by ferromagnetic layers antiferromagnetically coupled via non- magnetic spacers-called metamagnets-have caught the attention of the scientific community by its applicability in, for example, high-density data storage technologies or spintronics. In particular, the metamagnets that exhibit a strong anisotropy perpendicular to the layers have been described by an Ising metamagnet, where each layer consists of n bidimensional ferromagnetic sublayers. When an external magnetic field h is applied perpendicularly to the multilayer plane, its behavior depends on if the number of layers C is odd or even. On the one hand, if C is an odd, the ground state for low values of h is composed of ferromagnetic ordered layers that are coupled antiferromagnetically (AF phase). If h=2J/n, where J is the coupling exchange constant, a phase transition occurs to a paramagnetic phase, PM, where the spins are directed along the field axis [1]. On the other hand, if C is even, an intermediate phase (IP) appears. In the IP the top and bottom layers are aligned with h. As consequence two transitions are produced: AF-IP and IP-PM. This system has been extensively studied, and it has been demonstrated for T>0 that the AF-IP transition is of first-order and the IP-PM changes from first-order to continuous at a tricritical point [1,2]. Furthermore, the transitions lines depend on n for fixed C. Nevertheless, research on the phase behavior of anisotropic metamagnets with odd C is limited. Consequently, the characteristics of the AF-PM transition, the existence of a multicritical point, and the influence of C and n on the transition line in the (h,T) phase diagram remain unresolved. This work is devoted to study the phase diagram of anisotropic metamagnets with C=3, 5, 7, 9 and 11 for fixed n=2. Monte Carlo simulations were performed with periodic boundary conditions in the layer planes and open in the field direction. The dynamic evolution to the equilibrium state was registered and analyzed, and it is observed how the interfaces affect the coupling with the external field. By employing the short-time dynamics technique [3], the AF-PM transition line corresponding to the interval 3.65 ≤ T ≤ 4.50 and 0 ≤ h ≤ 1.0 was obtained. The results show that within this interval, the transition line is continuous and independent of C, changing its character at a tricritical point. Furthermore, the continuous transitions were characterized by estimating the critical exponents.
References
[1] Allbano E. V. Bab, M. A., Baglietto G., Borzi R., Grigera T. S., Loscar E., Rodriguez D. Rubio Puzzo M. L. and Saracco G. P., Rep. Prog. Phys 74, 026501 (2011).
[2] Mayberry J., Tauscher K., and Pleimling M., Phys. Rev. B, 90, 014438 (2014).
[3] Prudnikov P., Elin A., and Medvedeva M., J. of Phys. conf. series, 510, 012019 (2014).