Intertwined ferromagnetic and altermagnetic orders in Cr-doped MnTe

Abstract

Ferromagnetism and altermagnetism both break time-reversal symmetry, yet their distinct transformation properties under crystalline symmetries forbid direct bilinear coupling between their order parameters. Whether these two magnetic orders can remain thermodynamically distinct while strongly influencing one another remains an open question. Here we demonstrate the homogeneous coexistence of ferromagnetism and altermagnetism in Cr-doped MnTe. By tuning the ferromagnetic ordering temperature across the nearly unchanged Néel temperature with Cr doping, we uncover a striking interplay between the two orders: the ferromagnetic transition becomes a crossover when altermagnetism develops first, whereas the onset of altermagnetism strongly suppresses the out-of-plane ferromagnetic remanence when ferromagnetism develops first. Moreover, spin-orbit coupling enables symmetry-selective interactions through which the ferromagnetic moment controls the altermagnetic domain manifold, with its out-of-plane and in-plane components biasing the time-reversal ($Z_2$) and orientational ($Z_3$) sectors, respectively. Our results reveal how two symmetry-distinct magnetic orders can retain separate ordering tendencies while remaining strongly coupled, providing a route towards internal control of altermagnetic domain states.