Improper multiferroiclike transition in a metal

Magnetic frustration in insulators often induces cooperative atomic displacements to form a polar structure with long-range ordered electric dipoles, commonly known as improper multiferroics. In metals, such a multiferroic phenomenon is not expected to occur because free carriers tend to screen internal electrostatic forces, eliminating long-range ordered electric dipoles. To date, intrinsic multiferroiclike metals have rarely been reported. Here we present a spin-frustration-induced long-range antiparallel ordering of electric dipoles in metallic CrN with an unusual antiferromagnetic ground state. Two equivalent magnetic structures are also iden- tified and linked to two distinct antiparallel polar orders. Such a scenario is analogous to that of conventional improper multiferroics with a magnetic origin of polar transition. The order parameter of structural distortion is linearly coupled to the magnetic order due to a strong magnetoelectric effect. The multiferroiclike metal is in striking contrast to insulating multiferroics, offering an extraordinary archetype for probing new underlying physics and exploring unusual properties for practical applications.