Helical magnetism in Sr-doped CaMn7O12 films

Noncollinear magnetism can play an important role in multiferroic materials but is relatively understudied in oxide heterostructures compared to their bulk counterparts. Using variable temperature magnetometry and neutron diffraction, we demonstrate the presence of helical magnetic ordering in $\mathrm{CaM}{\mathrm{n}}_{7}{\mathrm{O}}_{12}$ and $\mathrm{C}{\mathrm{a}}_{1\ensuremath{-}x}\mathrm{S}{\mathrm{r}}_{x}\mathrm{M}{\mathrm{n}}_{7}{\mathrm{O}}_{12}$ (for $x$ up to 0.51) thin films. Consistent with bulk $\mathrm{C}{\mathrm{a}}_{1\ensuremath{-}x}\mathrm{S}{\mathrm{r}}_{x}\mathrm{M}{\mathrm{n}}_{7}{\mathrm{O}}_{12}$, the net magnetization increases with Sr doping. Neutron diffraction confirms that the helical magnetic structure remains incommensurate at all values of $x$, while the fundamental magnetic wavevector increases upon Sr substitution. This result demonstrates a chemical-based approach for tuning helical magnetism in quadruple perovskite films and enables future studies of strain and interfacial effects on helimagnetism in oxide heterostructures.