Magnetic Properties Of Rare Earth Nanoclusters

In recent years,the study of nano-magnetic materials has been widely used in science and technology.A great deal of research has been done in both experimental and theoretical calculations.Magnetic materials can be divided into soft magnetic materials and hard magnetic materials,The development and magnetic research of hard magnetic materials is a hot focus in the research field of new nanostructured materials.It is also a good vehicle for in-depth study of fundamental magnetic problems.The properties of nanometer magnetic materials and bulk magnetic materials are almost the same,and the properties of nanometer magnetic materials are related to their size.It is shown that the specific surface area of nanometer magnetic materials will decrease with the increasing of the size of the nanometer magnetic materials,leading to obvious changes in chemical and physical properties.Because rare-earth atoms contain unfilled 4f electron orbitals,they have very large spin-magnetic moments and orbital magnetic moments,It also allows the rare earth atoms to exhibit strong magnetic anisotropy,The reason is that the electrons in the 4f orbitals of rare-earth atoms have very strong local and spin-orbit coupling effects.Lanthanides（Ln）nanostructures have the potentials to meet the active demands of the miniaturization of advanced devices such as ultrahigh-storage densities in magnetic memory,owing to their excellent magnetic performance.However,many questions about the fundamental properties remain unsolved even for Ln bulk and smallest nanostructures.From both of application and scientific points of views,it is crucial to determine their structural stability,magnetic coupling,and magnetic anisotropy,Therefore,the in-depth study of rare earth nanoclusters is conducive to the development of new optoelectronic materials and magnetic materials.It is applied to high-tech materials such as spintronics,high-density magnetic storage and chemical catalysis.This paper studies the calculation method using the first principle.The structure,electron properties,spin-orbit coupling and magnetism of rare earth praseodymium nanoclusters（Pr_n（n=2-20））and samarium and cobalt nanoclusters(Sm₃Co₁₈)were studied theoretically.Then the structure and magnetism of Pr₁₂ and Pr₁₃ nanoclusters were investigated.The main research results of this paper are as follows:1.Density functional theory（DFT）calculation based on first principles,We systematically studied the structure,electron properties,spin-orbit coupling and magnetism of Pr_n（n=2-20）rare earth nanoclusters.With the help of experimental measurements on magnetic properties of Pr bulk and clusters,separated spin and orbital magnetic moments are quantitatively calculated by using the first-principle density functional theory（DFT）method,where spin-orbit coupling（SOC）and noncollinearity are included self-consistently.We found that Pr bulk is a singlet state within atomic magnetic moments anti-ferromagnetically coupled along in-plane direction,and it shows strong inplane magnetic anisotropy.The contribution to total moments from orbital magnetic moments is remarkable in bulk phase and clusters,obeying the Hund’s rule of negative values,however,they cannot determine the experimental magnetic oscillation of clusters.The oscillation behavior as the function of cluster sizes as well as the enhanced magnetic moment with increasing temperature that observed in experiment can be interpreted as the anti-ferromagnetic couplings between atomic moments.Giant magnetic anisotropy energy about several hundreds of meV is obtained in both Pr bulk and several clusters,which is an order of magnitude larger than transition metal counterparts.2.We used the generalized gradient approximation（GGA）and GGA+U methods in the first-principles method to calculate the Sm₃Co₁₈ nanometer clusters.The magnetic properties and structures of the nanoclusters are systematically studied,in which U represents the coulomb interaction modification.We studied the configuration of the geometry,the magnetism,and the symmetry of the entire cluster,as well as the contribution of the magnetism of each samarium atom（Sm）and cobalt atom（Co）in the structure to the magnetism of the entire nanocluster.The theoretical calculation of Sm₃Co₁₈ nanometer cluster is carried out by GGA+U calculation method,and the result is semi-metallic ferromagnetic state.Because of the strong hybrid interaction between the4f state of Sm and the 3d state of Co,the integer value of the total magnetic moment is of great significance to the properties of this semi-metallic material.Therefore,the spin magnetic moment,orbital magnetic moment and spin-orbit coupling（SOC）of Sm₃Co₁₈cluster have been calculated.We analyzed the calculated data and found that Sm atoms in different positions of the cluster would show significant changes in magnetic peaks,while the nanometer cluster materials composed of Co atoms and Sm atoms were hard magnetic materials of rare earth.The results show that the Sm atom in the middle of the caged spherical Sm₃Co₁₈ nanometer cluster is anti-ferromagnetic,and the magnetism is the largest.The magnetic enhancement of the nanoclusters provides a better design and research idea for the study of dual-magnetic phase composite nanocore-shell structure materials,and has a broad application prospect in the field of magnetic storage materials and optional electronics.