Design of Co/ Pd multilayer system with antiferromagnetic-to-ferromagnetic phase transition
Résumé
Among the known magnetic material systems, most are either purely antiferromagnetic or purely ferromagnetic at temperatures up to their critical temperature. There are only very few examples of materials that undergo a temperature dependent phase transition from an antiferromagnetic to a ferromagnetic phase or vice versa, and of these, only the chemically ordered alloy FeRh exhibits this transition near room temperature. Here we present a perpendicular anisotropy multilayer structure that by careful tuning of the constituent layers and their coupling mimics the magnetic behavior of FeRh, yet allows great flexibility in tuning its magnetic properties over a wide temperature range. The first order phase transition from an antiferromag-netic ͑AF͒ to a ferromagnetic ͑FM͒ phase in FeRh upon heating from room temperature to a transition temperature, T AF-FM , of approximately 370 K was discovered in 1938 by Fallot. 1 In subsequent experiments using Mössbauer spectroscopy 2 and neutron diffraction 3 the spin structure of the two phases was shown to be collinear with moments of 3.2 B per Fe and 0.9 B per Rh atom for the FM phase and 3.3 B per Fe atom and no magnetic moment on the Rh for the AF phase. While other materials exhibiting similar first order AF-to-FM phase transitions such as Ru-doped CeFe 2 are known, 4 FeRh is unique in that the phase transition occurs around room temperature. The transition temperature can be tuned over a wide range by substitutional doping: it increases with small additions of Ir or Pt, and decreases with small additions of Pd or Ni. 5 Recently, FeRh was investigated with renewed interest for potential applications in thermally assisted magnetic recording and memory devices. 6
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