Effect of diffusion sequence on magnetic properties and microstructures of two-step grain boundary diffusion treated Nd-Fe-B magnets

Effects of gadolinium and silicon substitution on magnetic properties and microstructure of Nd–Fe–B–Nb bulk nanocomposite magnets

Advanced machine learning techniques have unfurled their applications in various interdisciplinary areas of research and development. This paper highlights the use of image regression algorithms based on advanced neural networks to understand the magnetic properties directly from the magnetic microstructure. In this study, Co/Pd multilayers have been chosen as a reference material system that displays maze-like magnetic domains in pristine conditions. Irradiation of Ar+ ions with two different energies (50 and 100 keV) at various fluences was used as an external perturbation to investigate the modification of magnetic and structural properties from a state of perpendicular magnetic anisotropy to the vicinity of the spin reorientation transition. Magnetic force microscopy revealed domain fragmentation with a smaller periodicity and weaker magnetic contrast up to the fluence of 1014 ions/cm2. Further increases in the ion fluence result in the formation of feather-like domains with a variation in local magnetization distribution. The experimental results were complemented with micromagnetic simulations, where the variations of effective magnetic anisotropy and exchange constant result in qualitatively similar changes in magnetic domains, as observed experimentally. Importantly, a set of 960 simulated domain images was generated to train, validate, and test the convolutional neural network (CNN) that predicts the magnetic properties directly from the domain images with a high level of accuracy (maximum 93.9%). Our work has immense importance in promoting the applications of image regression methods through the CNN in understanding integral magnetic properties obtained from the microscopic features subject to change under external perturbations.

The magnetic properties and microstructure of barium ferrite films (BaFe12O19) coated by a sol-gel technique involving a spin coating of metal-organic compounds are investigated. The in-plane magnetic properties and the grain size are controlled by a Fe/Ba atomic ratio in the coating solution and annealing conditions. The in-plane coercivity increases as the decrease of the Fe/Ba ratio and the increase of the annealing temperature. Maximum value of 4–6 kOe is obtained at the Fe/Ba ratio of 2–8 with the annealing at 900 °C for 10 min. At these preparation conditions, the c axis of the hexagonal barium ferrite is slightly oriented parallel to the film plane. The grain size decreases as the decrease of the Fe/Ba ratio. The films with the Fe/Ba ratio of 4–6 show a grain size of almost one-tenth of that of the sputtered films without additives such as Cr2O3 or CoTi. The smaller grain size of the sol-gel-coated films is probably due to the high nucleation density at the annealing process.

Magnetic properties and microstructure of nanocomposite (Nd,Pr)–Fe–B ribbons by doping Nb element

The magnetic properties and microstructure of ultrathin Co films grown on a Si(111)-7×7 surface were investigated. The experimental results observed by surface magneto-optic Kerr effect (SMOKE) and scanning tunneling microscopy show that the surface morphological evolution of x ML (monolayer) Co∕Si(111) films is strongly related to their magnetic properties. Due to the formation of a CoSi2 layer, no magnetic signal could be detected by SMOKE for x=2.1. Both longitudinal and polar hysteresis loops appear for 4.2–8.5 ML Co∕Si(111) films because of their rougher surfaces. When the Co thickness is increased to 11 ML, a magnetic hysteresis loop only occurs in the longitudinal configuration, which can be attributed to the contribution of volume anisotropy. After annealing an 11 ML Co∕Si(111) film at 400 and 500K, the surface becomes rougher, inducing magnetic anisotropy on the polar configuration. When the annealing temperature was increased to 600K, however, the Co could react with Si to form a nonmagnetic cobalt silicide compound, and consequently, the hysteresis loops disappeared.

The effect of heat treatment on the magnetic properties and microstructure of electroless plated CoNiP films for use as perpendicular magnetic recording media was investigated, in order to clarify the film microstructure in the as deposited state, as well as to evaluate their thermal stability. The as-deposited film consisted of a mixture of ≪002≫ perpendicularly oriented hep structure, and fcc structure without any obvious crystal orientation. Heat treatment at temperatures above 400°C changed the dominant crystal structure from hep to fcc. The crystallites grow larger with heat treatment, causing a sharp change in magnetic properties. These changes were due to the disappearance of the magnetocrystalline anisotropy induced by the cobalt hep structure, and the decrease in the shape magnetic anisotropy due to the change in film topology. On the basis of these results, it is suggested that a compositional inhomogeneity due to the segregation of Co-rich regions exists in the as-deposited films; this segregation disappears with heat treatment at higher temperature, so that the crystal structure of the film changes to an fcc structure.

Magnetic properties and microstructures of high-performance Sm 2 Co 17 based alloy

Magnetic properties, phase evolution, and microstructure of melt spun Sm(Co1−zZrz)xCy (x=5–9; y=0–0.15; z=0.03 and 0.06) ribbons

Due to the large volume fraction of grain boundaries (GB’s) and a random orientation of the crystallographic axes, nanocrystalline inert-gas condensed materials are common model systems for investigating the impact of internal interfaces and reduced structural length scales on the macroscopic properties of real solids. In the lanthanide metals (LM’s), it may be expected that the indirect exchange coupling of the localized magnetic moments via the position-dependent RKKY-interaction renders magnetism particularly sensitive to structural imperfections associated with the GB’s. As a consequence of the vanishing angular momentum, Gd occupies a prominent position among the LM’s and is therefore exceptionally well-suited for studies in this field. Aiming at an understanding of the significance of defects for the ferromagnetic phase, a detailed knowledge of the magnetic microstructure in the bulk and on the relevant length scale of 1− 100 nm is required. Access to this type of data is, nearly exclusively, provided by the method of small-angle neutron scattering. However, due to the extraordinarily high absorption cross-section of natural Gd, such a study could not be realized so far. Employment of the low-capturing isotope Gd in the course of the present work has made it possible for the first time to perform such measurements. By using a combination of neutron scattering and magnetometry, the grain-size dependent magnetic microstructure of nanocrystalline Gd has been studied.

Bulk SrFe12O19/(Ni0.4Zn0.6)Fe2O4 composite ferrites with mass ratios Rm = 2 : 1, 1 : 1 and 1 : 2 were prepared using nanopowders obtained via a hydrothermal method, and their phase composition, magnetic properties, exchange coupling (EC) and magnetic microstructures were systematically investigated. It is found that all the bulk specimens sintered at either 700 or 900 °C are composed of two phases but exhibit typical single-phase magnetic behaviours, indicating the existence of EC between the magnetically hard and soft phases. However, too much (Rm = 2 : 1) or too little (Rm = 1 : 2) soft (Ni0.4Zn0.6)Fe2O4 phase weakens the EC in the composites. It is also proved that except for the EC, the strengthening of chemical polarization of the internal chemical bonds affects saturation magnetization, and the size of nanoscale grains significantly influences the EC and magnetic properties. In addition, novel stripe domains are found in all of the bulk composite specimens, which could be ascribed to the magnetization of the soft (Ni,Zn)Fe2O4 phase induced by the hard SrFe12O19 phase.

In recent years, to reduce manufacturing costs and decrease the rare-earth supply/demand imbalance in the Nd–Fe–B magnet market, (Nd,Ce)–Fe–B magnets, in which Nd is replaced by Ce, have gained significant attention. In this study, we investigated the magnetic properties and microstructures of anisotropic (Nd,Ce)–Fe–B powders treated by hydrogenation–disproportionation–desorption–recombination (HDDR). The demagnetization curve of Nd12.5Febal.B6.5Nb0.2 after the grain boundary diffusion (GBD) process exhibited high squareness, whereas that of (Nd0.5Ce0.5)12.5Febal.B6.5Nb0.2 exhibited low squareness with a knick. Generally, the low squareness of the demagnetization curve is caused by the presence of different HcJ regions in the material. The XRD, SEM, and STEM-EDX analyses revealed the generation of different HcJ regions owing to two factors. The first was the presence of a ferromagnetic RFe2 (R = Ce and Nd) phase surrounding the R2Fe14B phase, which was observed in the starting material after HDDR and GBD. Consequently, this region showed a lower HcJ than other typical regions in which the R2Fe14B grains were surrounded by an R-rich phase. The second was the inhomogeneous distribution of Ce and Nd in each R2Fe14B grain. This inhomogeneity stemmed from differences in the equilibrium conditions of the HDDR reaction between Nd2Fe14B and Ce2Fe14B, leading to variations in the magnetocrystalline anisotropy and HcJ in the R2Fe14B grains.

Some results concerning the magnetic and structural properties of [NdFeBNbCu∕Co]∙n thin films in view of their utilization for manufacturing permanent magnets are presented. As compared to Ta∕NdFeBNbCu∕Ta magnetic single layer, the multilayer Ta∕[NdFeBNbCu∕Co]∙3∕Ta films exhibit good hard magnetic properties and an increase in the Curie temperature due to Nb–Cu addition and stratification effect using Co as spacer layer. The influence of the additions content and the stratification effect on the microstructural and hard magnetic properties of multilayer [NdFeBNbCu∕Co]∙n thin films, when the total thickness of NdFeBNbCu layers was 540nm and the thickness of the Co spacer layers was varied successively from 0to6nm for different annealing conditions, are discussed.

Effects of oxygen and carbon on the magnetic properties and micro-structure of Sm 2Co 17 permanent magnets

Magnetic properties, microstructure and corrosion behavior of Nd10Y1Fe85−xNb3.5Ti0.5Bx (x = 14–22) and Nd10Y1Fe69Nb3.5M0.5B16 (M = Ti, Zr, Cr, Mo) bulk nanocrystalline magnets

The magnetic properties and microstructures of 2-17 type Sm-Co magnets with high Fe and low Zr content were investigated. The developed magnet achieved maximum energy product, [BH]m of 34.5 MGOe, intrinsic coercivity, Hcj of 21.3 kOe and squareness of 73.3% at 25 °C. Temperature coefficients of remanent magnetic flux density, Br and Hcj were 0.034%/K and 0.28%/K respectively, which values were almost as same as the conventional Sm-Co magnets. Moreover, the developed magnets had high magnetization orientation. For XRD, it was found that Zr was preferentially substituted by Co-Co pair, this made interaction between Co and Co stronger, so that heat resistance was maintained. Magnetic domain structures were observed with a Kerr effect microscope, and then it was observed that the developed magnet had strong pinning force. In the microstructures, the developed magnet had 200∼500 nm cell size with Fe and Cu separated clearly. This led to large gap of domain wall energy which produces strong pinning force. Because the developed magnet had high magnetization orientation and large gap of domain wall energy, we achieved high magnetic properties and high heat resistance on the developed magnet.