| High density magnetic storage materials and ultra-high magnetostrictive materials are two types of widely used magnetic functional materials. The performance of magnetic storage materials and magnetostrictive materials is scaled with magnetic anisotropy energy.The rapid development of information technology leads to the explosive growth of the amount of information, thus we need to continuously explore and develop high density magnetic storage materials. The density of traditional magnetic storage material has reached its bottleneck. The ultimate goal of the development of magnetic storage materials is to achieve atomic scale information storage. To realize the atomic scale information storage, many efforts have been devoted to seek a suitable substrate to host the magnetic storage bits. An important criterion to measure an ideal substrate material is to be able to make the recording unit to maintain large perpendicular magnetic anisotropy energy.As a novel magnetic functional material, magnetostrictive material is widely used for exploitations in sensors, actuators, micro electro mechanical system(MEMS), and energy harvesting devices. In general, besides a large magnetostriction coefficient, the magnetostrictive material should have excellent features including high mechanical strength, good ductility, low saturation magnetic field, high imposed-stress levels, and low associated cost. The large magnetostrictive coefficients are discovered in rare-earth 3d transition metal compounds, such as Terfenol-D(λ111>1000 ppm(10-6)). However, high value of magnetocrystalline anisotropy, high material costs and mechanical friability of these materials hinder their extensive industrial applications. Galfenol(Fe1-xGax) alloys are regarded as promising magnetostrictive materials for the next generation. Unfortunately, the magnetostrictive coefficient of Galfenol alloys is an order of magnitude smaller than the rare earth magnetostrictive materials. Moreover, the cost of single crystal growth is high and currently only in the laboratory stage. There is still a challenge to find new materials that exhibit high magnetostriction in a relatively low reversal magnetic field and good mechanical properties for technological innovations. The most crucial factor for the design of highly magnetostrictive materials is to have large magnetoelastic coupling: dEMCA/dε, i.e. a high response of magnetocrystalline anisotropy with strain.Therefore, the key factor to design high density magnetic storage materials and high magnetostrictive materials in theory is to calculate magnetic anisotropy energy precisely. From the view of practical application, the main results of our study are organized as follows:The key issue in this realm is how to increase the magnetic anisotropy energy(MAE), which denotes the threshold energy barrier for inhibiting magnetization reversal against thermal fluctuations. Due to the strong SOC of 5d TM systems, we investigated the magnetic properties of 5d transition metal(TM) atoms at porous sites of graphene-like carbon nitride(g-C3N4) using density functional theory. Our results show that the TM adatoms bind to g-C3N4 much stronger than to graphene due its unique porous structure. The magnetic anisotropy energies(MAEs) for TM doped g-C3N4 are investigated by using torque method. Huge MAEs are obtained, especially for Ir@g-C3N4 12.4 me V/atom with an easy axis perpendicular to the plane. Furthermore, using the rigid band model analysis, we propose that the MAE of Ir@g-C3N4 can be tuned by applying a moderate electric field. Interestingly, the MAE can be enhanced to 56.9 me V/atom by applying electric field up to 1.0 V/ ?. Our present study identifies g-C3N4 as an excellent template for TM atom adsorption.Applying magnetic nanostructures in high density magnetic data storage is hindered by a lack of suitable substrate. Using density functional theory, we explored the potentiality of graphyne as template for nanomagnetic bits. Due to the unique porous structure of graphyne, Os atom tightly binds to the graphyne at the hollow site with an in-plane MAE of 18 me V. Using rigid band model analysis, we introduced the strategy to manipulate the MAE by rearrangement of d-orbitals occupancy of Os atom through nonmetal functionalization. Huge MAE about 48 meV obtained for F functionalized Os@graphyne. To obtain the out-of-plane easy axis, we have considered the MAE of several transition-metal combinations. To obtain the out-of-plane easy axis, we have investigated the MAE of the TM combinations. In view of MAE=34.5 meV and high structural stability, we finally identified Os-Os@graphyne as an excellent candidate for room temperature applications. Our studies may pave an effective way towards robust nanomagnetic units for high density magnetic record.Another important way of manipulating magnetic anisotropy energy is applying strain. In order to explore the effect of strain on magnetic anisotropy energy, we investigate the magnetostriction of γ-Fe4 N by using the first-principles full-potential linearized augmented plane wave method. Its magnetostrictive coefficient is found to be-143 ppm. In order to enhance the magnetostriction, the derivative MnFe3 N is taken into our consideration according to the rigid band model. Interestingly, we find that the magnetostrictive coefficient is enhanced to be +373 ppm. To further improve the magnetostriction, we calculate the magnetostrictive coefficient of the derivatives containing 4d and 5d metal due to their strong spin-orbit coupling. The results show that the magnetostrictive coefficient can reach to-564 ppm and +416 ppm for OsFe3 N and IrFe3 N. Our calculations give a guideline for designing giant magnetostriction material.We investigated the stability, elastic and magnetostrictive properties of γ-Fe4 C and its derivatives MFe3N(M = Pd, Pt, Rh, Ir) through extensive FLAPW calculations. From the formation energy, we show that the most preferable configuration for MFe3C(M = Pd, Pt, Rh, Ir) is that the M atom occupied at the corner 1a position rather than 3c position. These derivatives are ductile due to high B/G values except for IrFe3 C. The calculated tetragonal magnetostrictive coefficient λ001 value for γ-Fe4 C is-380 ppm, which is larger than the value of Fe83Ga17(+ 207ppm). Due to the strong SOC coupling strength constant(ξ) of Pt, the calculated λ001 of PtFe3 C is-691 ppm, which is increased 80% compared to γ-Fe4 C. We demonstrate the origin of giant magnetostriction coef?cient in terms of electronic structures and their responses to the tetragonal lattice distortion. |
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