Non-collinear magnetic structure of the MAX phase Mn2GaC epitaxial films inferred from zero-field NMR study (CE-5:L05)

Abstract

Zero-field NMR investigations on the 69Ga, 71Ga, and 55Mn nuclei have been performed at 4.2 K on a 100 nm thick epitaxial Mn2GaC(0001) MAX phase film grown on a MgO(111) substrate. This nano-laminated structure consists of ferromagnetic Mn–C–Mn stacks interleaved with monolayers of gallium. A resolved quadrupolar structure of the observed gallium resonances is a fingerprint of a well-defined crystal field confirming high crystal quality. The nuclei of non-magnetic gallium atoms are shown to experience the transferred hyperfine magnetic field of 15.75 T (±0.05 T), which is due to polarization of their 4s electron shell by the magnetic moments of manganese neighbors, evidencing the presence of an uncompensated ferromagnetic moment within the manganese sublattice. The average magnetic moment of manganese was found to be around 2 μB, strongly contrasting with the reported remnant magnetization of only 0.3 μB. Moreover, the 55Mn NMR spectrum indicates the presence of magnetically non-equivalent manganese sites within this structure. The observed features of the 69,71Ga and 55Mn NMR spectra cannot be reconciled with any of the hitherto proposed collinear arrangements of manganese moments and suggest their non-collinear arrangement across a gallium layer. Nevertheless a more advanced study is required to elucidate the detailed nature of magnetic structure in this material.