Multiferroic phase transition between multiple types of collinear compensated magnets

Achieving reversible ferroic control over distinct compensated magnetic states is of fundamental importance for developing reconfigurable spintronic functionalities, yet remains a nontrivial challenge. Here we predict that layered hybrid-improper multiferroics provide a broadly applicable platform for such interconversion in the monolayer or few-layer limit. Using monolayer K₃Mn₂Cl₇ as a representative example, whose bulk multiferroicity has been experimentally established, we show that its magnetic ground state is an insulating compensated magnet with in-plane ferroelectric polarization, and that ferroic control can drive reversible multiferroic phase transitions among multiple types of compensated magnets. The (anti)ferroelectric states here retain spin degeneracy in the nonrelativistic limit but acquire full-space persistent spin texture and transport responses. Interestingly, both ferroelectric and antiferroelectric states exhibit sign-reversible Hall transport without exchange splitting reversal found in conventional compensated magnets, revealing an unexplored form of magnetoelectric coupling. These results establish layered hybrid-improper multiferroics as promising building blocks for programmable spintronics.