First-Principles Study On Magnetic Anisotropy Of Magnetic Memory Cell And Its Regulation

With the rapid development of modern science and technology,as well as the emergence of the Internet,big data,cloud storage and other technologies,hundreds of billions of data are generated in our lives every moment.Today,we have entered a new era of big data,and data has become one of the most important resources in the development of human society.The urgent need for data storage is driving the boom of storage technology.Therefore,the search for non-volatile,high-density,low-power consumption and high-speed read and write storage technology is an inevitable trend in the development of the information storage industry.The emergence of magnetic random access memory（MRAM）provides the possibility to solve these problems,which not only has the ability to read and write quickly from static random access memory（SRAM）and the advantages of large capacity and low cost of dynamic random access memory（DRAM）,but also has the characteristics of non-volatile and infinite erasing and writing.It has become,one of the most promising storage technology solutions in the future.High-density information storage has always been one of the main research goals pursued by the magnetic storage industry for a long time.Increasing the density of information storage means that the physical size of magnetic storage cells is constantly shrinking,and this reduction in physical size will lead to the instability of the stored information.Magnetic anisotropy is an important parameter that determines the stability of magnetic storage information,but high magnetic anisotropy will lead to difficulty in information writing,and the development of magnetic storage units with large and adjustable magnetic anisotropy is the main strategy to solve this dilemma.In this paper,the large magnetic anisotropy of Mg O/Rh₂Co Sb heterojunction system and X/In₂Se₃（X is 3d transition metal single atom）magnetic single-atom adsorption system was studied by first-principles calculations,and the magnetic anisotropy of Mg O/Rh₂Co Sb and X/In₂Se₃was regulated by applying voltage and ferroelectric polarization,respectively.The detailed work contents are as follows:（1）Rh₂Co Sb is a novel Heusler alloy recently reported.Experiments and calculations have shown that it is a hard magnet with large magnetic anisotropy and spin polarization.Up to now,the heterojunction system formed by Rh₂Co Sb and Mg O substrates has not been studied.In this paper,using first-principles calculations,we study two interface structures of Mg O/Rh₂Co Sb（Mg O/Rh₂...Rh₂and Mg O/Co...Co Sb）,and analyze the contribution of Rh and Co elements to magnetism.In addition,the dependence of magnetic anisotropy（MA）on the electric field in the Mg O/Rh₂Co Sb heterojunction system is also studied.We find that the Mg O/Rh₂Co Sb heterojunction system with Rh as the terminated atoms of interface has perpendicular MA（PMA）with huge VCMA coefficient of 7024 f J/Vm.The VCMA coefficient exhibits the characteristics of dependence on the direction of the electric field.Through orbital resolved MA and second-order perturbation theory,we analyze the origin mechanism of these calculated results.The VCMA effect can be attributed to the redistribution of d orbitals near the Fermi level under electric field.（2）The magnetic anisotropy of transition metal atoms X（X=Co,Fe,Ir,Mo,Nb,Ta,Ti,V,W）adsorbed on the surface of the two-dimensional ferroelectric In₂Se₃is studied by first-principles calculations.We find that when the ferroelectric polarization direction of In₂Se₃is switched,the magnetic anisotropy strength of Co,Ir,Nb,and Ti single atoms changes,while the magnetic anisotropy direction of Fe,Mo,Ta,V,and W single atoms is flipped.The calculated electronic structure and orbital-resolved magnetic anisotropic energy show that the change of occupied spin minority states and the exchange splitting of the d orbital on the Fermi level caused by switching ferroelectric polarization are the reasons for the changes in the intensity and direction of magnetic anisotropy on the X atoms.