Research On Magnetic Properties Of Skyrmions In Magnetic Orbit

The ultra-density information storage and spin-magneto-oscillation devices based on Skyrmions have drawn great attention because of their small size(several nanometers)and low current density used to drive Skyrmions.It is very important to study the magnetic properties of Skyrmions in magnetic nanometer orbit.In this thesis,we studied the basic magnetic properties of Skyrmions in magnetic orbits using micromagnetic simulation.Combined with the existing single-free layer structure based on Skyrmions spin-transfer torque nano-oscillator,we proposed a dual free-layer model and a device model that could further change the Skyrmions precession rate and the core diameter by voltage-controlled magnetic anisotropy,obtained an inter-layer coupling energy density range that guarantees the synchronous transition of Skyrmions in the dual free-layer and given Skyrmions a precession in the above two models.Firstly,we observed the change of the core diameter of Skyrmions in the nanodisks by adjusting the Dzyaloshinskii-Moriya effect coupling coefficient D and the anisotropy constant K,and induced its nucleation by means of polarized current injection;Then driving a single Skyrmions and Skyrmions-Skyrmions in a long magnetic orbit to the end by applying in-plane polarized current at the front of the orbit.Simulation results showed that isolated Skyrmions nuclear diameter increased with the increase of coupling coefficient D,in contrast to the anisotropy constant K.Skyrmions nucleation effect was relatively good when the coupling coefficient D was 5~6mJ/m2 and the polarization current density J was 2×1012A·m-2~5×1012A·m-2.The rate of motion of Skyrmions was positively related to the polarization current density,and the maximum distance required for Skyrmions to interact with orbit end and the other one were about 25 nm and 45 nm,respectively.Isolated Skyrmions and double Skyrmions could be circular motion in the disc track.Secondly,we deduced the output power expression of the dual free-layer model,which showed that the structure could double the output power.Then we analyzed the precession of Skyrmions in the two free layers in the vertical position and the non-vertical symmetry at the initial position by applying a polarizing current in the center of the disc.The results showed that,in the case of vertical symmetry,Skyrmions could be synchronized in two layers.In the case of non-vertical symmetry,skyrmions nuclear areas were destroyed,when the energy density of the inter-layer exchange coupling was greater than 0.01mJ/m2.When the value was equal to or less than 0.01mJ/m2,stable synchronous precession could be achieved,and the system energy was the lowest.Its working period was 13.8ns,the precession frequency was 0.08 GHz.Finally,according to the voltage-controlled magnetic anisotropy effect,a voltage could be applied in the Skyrmions precession orbit region,and we analyzed two kinds of cases of applying constant voltage signal and square wave voltage signal.The results showed that,under constant voltage signal,the precession rate and the core diameter of Skyrmions decreased with the increase of the magnetic anisotropy constant Kuv.Under square wave voltage signal,there was a 2.5ns stagnation period in the preamble,and the nuclear diameter of Skyrmions increased during the period,but there was no obvious precession.After entering the steady precession period,the precession rate and the nuclear diameter were adjusted within 2.5ns after the regulation voltage changed.