Magnus Induced Magnetic Diode Effect in Skyrmion Systems

Abstract: We show that skyrmions can exhibit what we call a magnetic diode effect, where there is a nonreciprocal response in the transport when the magnetic field is reversed. This effect can be achieved for skyrmions moving in a channel with a sawtooth potential on one side and a reversed sawtooth potential on the other side. We consider the cases of both spin-transfer torque (STT) and spin-orbit torque (SOT) driving. When the magnetic field is held fixed, the velocity response of the skyrmion is the same for current applied in either direction for both STT and SOT driving, so there is no current diode effect. When the magnetic field is reversed, under STT driving the velocity of the skyrmion reverses and its absolute value changes. Under SOT driving, the velocity remains in the same direction but drops to a much lower value, resulting in negative differential conductivity. For a fixed current, we find a nonreciprocal skyrmion velocity as a function of positive and negative applied fields, in analogy to the velocity-current curves observed in the usual diode effect. The nonreciprocity is generated by the Magnus force, which causes skyrmions to interact preferentially with one side of the channel. Since the channel sides have opposite asymmetry, a positive magnetic field can cause the skyrmion to interact with the "hard" asymmetry side of the channel, while a negative magnetic field causes the skyrmion to interact with the easy asymmetry side. This geometry could be used to create new kinds of magnetic-field-induced diode effects that can be harnessed in new types of skyrmion-based devices.