Helical magnetic structure of epitaxial films of nanolaminated Mn2GaC MAX phase

Nanolaminated ${\mathrm{Mn}}_{2}\mathrm{GaC}$ epitaxial films crystallizing in the hexagonal structure belong to the family of MAX phase compounds and display complex magnetic interactions. While the critical temperature of the order-disorder transition is 507 K, at around 214 K this compound undergoes a first-order phase transition with the magnetic structure below the transition point not being fully resolved. Previous studies indicated a noncollinear spin arrangement, but a specific magnetic structure could not be defined. In this work we present the results of $^{69}\mathrm{Ga}, ^{71}\mathrm{Ga}$, and $^{55}\mathrm{Mn}$ NMR experiments performed at 4.2 K in an external in-plane magnetic field up to 1 T. The in-depth analysis of the experimental results shows a helical magnetic structure consisting of the ferromagnetically coupled Mn-C-Mn slabs that are twisted across the Ga layer by $167.{2}^{\ensuremath{\circ}}$ with respect to the next Mn-C-Mn slab. As a result, the magnetic structure presents a spiral propagating along the out-of-plane direction (hexagonal $c$ axis) with a pitch of around 14 lattice constants.