Exchange-spring behavior in epitaxial hard/soft magnetic bilayers

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Abstract
We present results on the magnetic reversal process in epitaxial Sm-Co(11¯00)/TM (TM=Fe,Co) bilayer films prepared via magnetron sputtering. The magnetically hard Sm-Co films have 20-T uniaxial anisotropy and coercivities >3 T at room temperature, that double on cooling, as determined by magnetometry. The TM layers are exchange coupled to the Sm-Co layer and exhibit reversible demagnetization curves expected for an exchange-spring magnet. We also present numerical solutions of a one-dimensional model that provide the spin configuration for each atomic layer. Comparison of the experimental results with the model simulations indicates that our exchange-spring behavior can be understood from the intrinsic parameters of the hard and soft layers. The simulations are extended to realistically estimate the ultimate gain in the energy product that potentially can be realized based on the exchange hardening principle.