Magnetic properties of hard/soft composites: SmCo5/Co1−xFex

First-principles calculations are carried out to study the magnetic hardening of $\left({\mathrm{SmCo}}_5\right)/\left({\mathrm{Co}}_{1-x}{\mathrm{Fe}}_x\right)$ multilayers. The multilayer stacking along the c axis of the hexagonal hard phase $\left({\mathrm{SmCo}}_5\right)$ and the (111) direction of the fcc soft phase $\left({\mathrm{Co}}_{1-x}{\mathrm{Fe}}_x\right)$ is well matched structurally. The self-consistent spin-polarized electronic structure results are used to calculate the magnetic moments and the exchange interaction parameters. The average magnetic moments of the soft $\left({\mathrm{Co}}_3\mathrm{Fe}\right)$ and hard phases are $1.83{\mu }_B$ and $1.2{\mu }_B$ per atom, respectively. A continuum model of the periodically layered hard/soft composite predicts the optimum thickness of the soft phase to be approximately 13 nm independent of the thickness of the hard phase. Calculated exchange parameters predict the Curie temperature of the hard/soft system to be between the values for each phase (1000–1388 K) depending on the relative thicknesses of the two phases. The optimum theoretical limit to the energy product of the composite is ∼65 MGOe, which is almost twice the value for the hard phase.