Magnetocrystalline anisotropy of epitaxial MnPt thin-films

Antiferromagnetic (AFM) spintronics is a promising path towards ultrafast scalable information storage and processing technologies. Yet quantitative knowledge of key material parameters for many AFMs is lacking due to the difficulty of controlling the AFM order parameter. Here we demonstrate that measurements of the angular dependence of ferromagnetic resonance (FMR) in MnPt/ Ni₈₀Fe₂₀ bilayers allow us to probe magnetocrystalline anisotropy of the MnPt AFM. For this study, epitaxial L1₀-Mn₅₀Pt₅₀ films in the thickness range from 6 nm to 22 nm were grown onto a MgAl₂O₃ (100) substrates, followed by deposition of polycrystalline Ni₈₀Fe₂₀ as the ferromagnetic (FM) coupling layer. FMR measurements reveal a 4-fold in-plane anisotropy in Ni₈₀Fe₂₀ imparted from the MnPt layer by the interlayer exchange coupling. An analytical model of exchange coupling in FM/AFM bilayers was used to show that the observed anisotropy in the FM layer directly relates to magnetocrystalline anisotropy in the coupled AFM. Analysis of the dependence of the induced 4-fold anisotropy on the AFM layer thickness allows us to quantify the magnetocrystalline anisotropy of MnPt.