Multiferroic Phase Transition between Four Types of Collinear Compensated Magnets

Collinear compensated magnets—encompassing ferrimagnets, antiferromagnets, altermagnets, and the recently identified type-IV class—host zero net magnetization while enabling diverse spin-polarization patterns and unconventional transport responses beyond ferromagnetic systems. However, realizing electric-field control across four compensated magnetic states has remained a fundamental challenge. Here, we reveal that an experimentally established layered hybrid-improper multiferroic, K3Mn2Cl7, realizes such long-sought functionality in the monolayer limit. We show that its magnetic ground state is an intrinsic insulating type-IV magnet with in-plane ferroelectric polarization, and that electric fields can drive reversible multiferroic phase transitions among four types of compensated magnets. Distinct from previously studied ferrimagnetic or altermagnetic multiferroics, the compensated type-IV states retain spin degeneracy in the nonrelativistic limit but acquire symmetry-governed full-space persistent spin texture, topological and transport responses. Interestingly, both ferroelectric and antiferroelectric type-IV magnetic domains exhibit sign-reversible anomalous Hall transport without exchange splitting reversal found in conventional compensated magnets, revealing a previously unexplored form of magnetoelectric coupling in van der Waals multiferroics. Our work establishes K3Mn2Cl7 as a rare platform where ferroicity, various compensated magnetism, and Berry-phase transport are intrinsically intertwined, opening a route to electrically programmable spintronic architectures.