Study On The Growth And Spin Wave Of Yttrium-Iron-Garnet-Based Heterostructures

The development of emerging technologies such as 5G,big data,and artificial intelligence has put forward higher requirements for the computing and storage capabilities of electronic devices.However,the traditional integrated circuit technology based on the CMOS process cannot meet the requirements of further integration and miniaturization of electronic devices due to the limitation of quantum tunneling effect and Joule heating.Spin wave（magneton）technology exploits the spin properties of electrons for information transmission,processing and storage,and shows great potential for breaking the limits of Moore’s Law.Yttrium iron garnet（YIG）films have the lowest known damping and are currently the best medium material for carrying spin waves.And the excitation of spin waves in nanoscale YIG films is of great importance for the miniaturization and integration of devices.1.High quality nanoscale YIG epitaxial thin films were prepared by pulsed laser deposition（PLD）.By investigating the effects of substrate temperature and growth oxygen pressure on the phase and magnetic properties of YIG epitaxial films,the optimal deposition conditions were obtained:substrate temperature of 750℃ and growth oxygen pressure of 8 Pa;under these deposition conditions,nanoscale YIG epitaxial films with ultra-low damping and narrow linewidth were prepared.For YIG film with a thickness of 30 nm,the damping constant was found to be as low as 2.2×10^-4.2.The excitation of spin waves in YIG/Py heterostructures has been investigated using ferromagnetic resonance techniques.It was found that perpendicular spin standing wave（PSSW）modes were excited in both the YIG and Py layers of the YIG/Py heterostructures under the action of an in-plane magnetic field and a microwave magnetic field provided by a coplanar waveguide（CPW）.The excitation of the PSSW modes in the Py layer was correlated with the pinning of the YIG layer.The excitation of the multi-order PSSW modes in the YIG layer is also related to the neighboring Py layer;and their intensities are enhanced when they approach the ferromagnetic resonance（FMR）modes of YIG and Py layers,as well as the PSSW modes of Py layer,accompanied by an anti-cross phenomenon;and reduced when they are far away.The excitation of the PSSW in the YIG layer is explained using the dynamic exchange torque of the interface.Further,the spin waves in the YIG/Py heterostructures were further investigated when an out-of-plane magnetic field is applied and it was found that the number of spin wave modes in an out-of-plane magnetic field did not change compared to that in an in-plane magnetic field.As the angle of the magnetic field rotating out of the film plane increases,both the resonant field and the resonant linewidth of each spin wave mode gradually increase.3.The growth and dynamic magnetism of YIG/NiO/YIG all-oxide heterostructures were investigated.We first explored the process conditions for the growth of NiO films by PLD and observed their antiferromagnetic domains.Spin wave excitation in NiO/Py heterostructures was further investigated,and it was found that PSSW modes could be excited in the Py layer under the pinning of the NiO layer,and the variation in the thickness of the NiO layer had no effect on the position of the PSSW mode spectral lines.Finally,we prepared YIG/NiO/YIG all oxide heterostructures and studied their dynamic magnetic properties.The results showed that the NiO intermediate layer would affect the crystal quality and dynamic magnetic properties of the upper YIG layer.By controlling the thickness of the intermediate NiO layer,high-quality epitaxial growth of the upper YIG layer can be achieved,and further YIG/NiO/YIG all-oxide heterostructures with low damping and double resonance peaks can be obtained.