Rare earth free alloys are in focus of permanent magnet research since the accessibility of the elements needed for nowadays conventional magnets is limited. Tetragonally strained iron-cobalt (Fe-Co) has attracted large interest as promising candidate due to theoretical calculations. In experiments, however, the applied strain quickly relaxes with increasing film thickness and hampers stabilization of a strong magnetocrystalline anisotropy. In our study we show that already 2 at% of carbon substantially reduce the lattice relaxation leading to the formation of a spontaneously strained phase with 3 % tetragonal distortion. In these strained (Fe0.4Co0.6)0.98C0.02 films, a magnetocrystalline anisotropy above 0.4 MJ/m3 is observed while the large polarization of 2.1 T is maintained. Compared to binary Fe-Co this is a remarkable improvement of the intrinsic magnetic properties. In this paper, we relate our experimental work to theoretical studies of strained Fe-Co-C and find a very good agreement.
@article{arxiv.1409.4952,
title = {Increased magnetocrystalline anisotropy in epitaxial Fe-Co-C thin films with spontaneous strain},
author = {Ludwig Reichel and George Giannopoulos and Sandra Kauffmann-Weiss and Martin Hoffmann and Darius Pohl and Alexander Edström and Steffen Oswald and Dimitris Niarchos and Jan Rusz and Ludwig Schultz and Sebastian Fähler},
journal= {arXiv preprint arXiv:1409.4952},
year = {2015}
}