Formation of phase domain structures in thin films under conditions of a first-order magnetic phase transition
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SORDER, AND PHASE TRANSITION IN CONDENSED SYSTEMS
Formation of Phase Domain Structures in Thin Films under Conditions of a First-Order Magnetic Phase Transition Yu. I. Dzhezherya and A. I. Tovstolytkin* Institute of Magnetism, National Academy of Sciences of Ukraine, bul’v. Vernadskogo 36b, Kiev, 03142 Ukraine * e-mail: [email protected] Received April 10, 2008
Abstract—This paper reports on the results of a theoretical investigation into the magnetic and resonance properties of thin films in the range of the transition from a paramagnetic state to a ferromagnetic state in the case where the magnetic transition is a first-order phase transformation. It is demonstrated that, in an external magnetic field directed perpendicular to the film plane, the formation of a specific domain structure consisting of domains of the coexisting paramagnetic and ferromagnetic phases can appear to be energetically favorable. The parameters of the equilibrium system of stripe phase domains and their dependences on the temperature, the magnetic field, and the characteristics of the material are calculated. The specific features of the magnetic resonance spectra under the conditions of formed stripe phase domains are considered. A relationship is derived for the dependence of the resonance field of the system of ferromagnetic domains on the magnetization and temperature. It is shown that the alternating external field can fulfill an orientation function in the formation of stripe phase domains. PACS numbers: 75.70.-i, 75.30.Kz, 76.50.+g DOI: 10.1134/S1063776108110095
1. INTRODUCTION The problems associated with the coexistence of phases in the course of first-order magnetic phase transitions have attracted the particular attention of researchers since the 1960s [1–3]. In the last years, interest in these phenomena has considerably quickened because of the observation of first-order phase transitions in materials that are promising for the use in devices intended for magnetic recording and reading of information [4–6]. It should be noted that rapid progress in experimental techniques in recent years has made it possible to gain a deeper insight into the effects accompanying first-order phase transitions and, in turn, led to the necessity of their more detailed analysis and interpretation [7–9]. In [1, 2, 10–12], it was shown that, at specific ratios between the exchange, elastic, and magnetoelastic constants of a magnet, the phase transition between paramagnetic (PM) and ferromagnetic (FM) or antiferromagnetic states can occur as a first-order phase transformation. The character of the transition from a disordered (paramagnetic) state to a magnetically ordered state can be determined from Arrott–Belov plots [3, 13]. The criterion for the first-order phase transition was proposed by Rodbell and Bean [1] and Novak et al. [14]. The inference was made that the type of magnetic transition is determined by the degree of the dependence of the exchange energy on the interatomic distance.
Phase transitions between two magnetically ordered state
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