Design of Co/Pd multilayer system with antiferromagnetic-to-ferromagnetic phase transition

Among the known magnetic material systems there are only very few examples of materials that undergo a temperature dependent antiferromagnetic-to-ferromagnetic phase transition, and of these only the chemically ordered alloy FeRh exhibits this transition near room temperature [1, 2]. Here we present a perpendicular anisotropy multilayer structure that mimics FeRh. The basic idea is to use two stacks of Co/Pd multilayers with large perpendicular magnetic anisotropy and high Curie temperature, T$_{C}$, separated by a layer providing antiferromagnetic coupling, and a CoNi/Pd multilayer with perpendicular anisotropy with a lower T$_{C}$, interlayer, in the range of the desired AF-FM transition temperature, T$_{AF-FM}$. At room temperature this system behaves as two antiferromagnetically coupled layers with a low perpendicular remanent magnetic moment. As the temperature is raised to approach T$_{C}$, $_{interlayer}$ the magnetization of the interlayer is gradually reduced to zero, and consequently its coupling strength is reduced. Eventually, the effective coupling between the two high-K$_{U}$, high-T$_{C}$ layers becomes dominated by their dipolar fields, resulting in a parallel alignment of their moments and a net remanent magnetic moment equal to the sum of the moments of the two high-T$_{C}$ layers [2]. \\[4pt] [1] J. S. Kouvel and C. C. Hartelius, J. Appl. Phys. \textbf{33} (1962) p1343 \\[0pt] [2] J.-U. Thiele, E. E. Fullerton, S. Maat, Appl. Phys. Lett. \textbf{82} (2003) p2859 \\[0pt] [3] J.-U. Thiele. T. Hauet. O. Hellwig, Appl. Phys. Lett. \textbf{92} (2008) 242502.