Static and dynamic magnetic properties of polycrystalline MnCoAl thin films

Half-Heusler alloys belong to the family of Heusler alloys which are actively studied as compounds with multifunctional properties. Very few magnetic half-Husler alloys were studied experimentally. One of these alloys, known from 1960s, is the MnCoAl in which an off-stoichiometric ferrimagnetic phase was detected in the bulk with a high Curie temperature (460K). Theoretical studies show that the stoichiometric ferrimagnetic phase, if stable, is close to half-metallicity displaying a pseudogap at the Fermi level. We succeeded in growing thin films of MnCoAl on two different substrates and we studied their structural, static and dynamic magnetic properties by XRD, SEM, TEM, SQUID magnetometry and ferromagnetic resonance (FMR). We found that our samples display ferrimagnetic properties (with Tc close to 500K) that depend on growth or annealing temperature, but also on samples thickness. At low temperature, the coercive field and remanent magnetization strongly increase up to 1200 Oe and 0.63 squareness ratio compared to 30 Oe and 0.04 at room temperature. Magnetic relaxation measurements by FMR point to important extrinsic mechanisms of damping present related with the films structure. Our study paves the way for future research on magnetic half-Heusler thin films.