Spontaneous magnetic diode effect in Co$_{1/3}$TaS$_2$

Overview & Synopsis

When electrons move through non-trivial spin textures in magnetic metals, conduction electrons couple to magnetic order through both their charge and their spin, acquiring non-trivial equations of motion and a dynamic spin polarization providing the foundation of spintronics. These mechanisms are, however, almost invariably reciprocal and the resistance a current encounters does not depend on its flow direction. Here we show that a chiral crystal lattice and an independently reversible chiral magnetic order together produce a diode whose forward direction is set by the magnetism rather than by the structure. In the triangular-lattice antiferromagnet Co$_{1/3}$TaS$_2$, whose chiral lattice hosts a chiral magnetic order of its own, independent handedness, we observe a pronounced nonreciprocal resistance. Unlike conventional electrical magnetochiral anisotropy, which is driven by an external magnetic field, our spontaneous magnetic diode effect arises from an internal noncoplanar spin texture with vanishing net magnetization. Symmetry analysis and model calculations show that the effect originates from the interplay of noncoplanar spin order and spin-orbit coupling, which generates a chiral, time-reversal-symmetry-breaking electronic response. Crucially, reversing the magnetic handedness reverses the sign of the nonreciprocal resistance, demonstrating magnetic control of the diode polarity.