Combinations of nontrivial band topology and long-range magnetic order hold promise for realizations of novel spintronic phenomena, such as the quantum anomalous Hall effect and the topological magnetoelectric effect. Following theoretical advances, material candidates are emerging. Yet, so far a compound that combines a band-inverted electronic structure with an intrinsic net magnetization remains unrealized. ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ has been established as the first antiferromagnetic topological insulator and constitutes the progenitor of a modular $({\mathrm{Bi}}_2{\mathrm{Te}}_3{)}_n({\mathrm{MnBi}}_2{\mathrm{Te}}_4)$ series. Here, for $n=1$, we confirm a nonstoichiometric composition proximate to ${\mathrm{MnBi}}_4{\mathrm{Te}}_7$. We establish an antiferromagnetic state below 13 K followed by a state with a net magnetization and ferromagnetic-like hysteresis below 5 K. Angle-resolved photoemission experiments and density-functional calculations reveal a topologically nontrivial surface state on the ${\mathrm{MnBi}}_4{\mathrm{Te}}_7(0001)$ surface, analogous to the nonmagnetic parent compound ${\mathrm{Bi}}_2{\mathrm{Te}}_3$. Our results establish ${\mathrm{MnBi}}_4{\mathrm{Te}}_7$ as the first band-inverted compound with intrinsic net magnetization providing a versatile platform for the realization of magnetic topological states of matter.

The magnetic properties of the van der Waals magnetic topological insulators ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ and ${\mathrm{MnBi}}_4{\mathrm{Te}}_7$ are investigated by magnetotransport measurements. We evidence that the relative strength of the interlayer exchange coupling $J$ to the uniaxial anisotropy $K$ controls a transition from an $A$-type antiferromagnetic order to a ferromagneticlike metamagnetic state. A bilayer Stoner-Wohlfarth model allows us to describe this evolution, as well as the typical angular dependence of specific signatures, such as the spin-flop transition of the uniaxial antiferromagnet and the switching field of the metamagnet.