Magnetic properties of SmCo-based permanent magnetic films during 25 to 300 ℃

Magnetic properties of the SmCo-based permanent magnetic films prepared on hot substrate with Mo and Cr underlayer without subsequent annealing process were investigated by vibrating sample magnetometer （VSM）, X-ray diffraction （XRD）, and en- ergy dispersive X-ray spectroscopy （EDS）. The results showed that the film thickness of the SmCo-based films presented complex effect on the intrinsic coercivity Hci. Optimal Hc~ for the films with Mo underlayer, Cr underlayer, and without underlayer was ob- served with different film thicknesses. Furthermore, the monotonous temperature dependence of Hci was found to be strongly corre- lated with the magnetic parameters for the 3.0 μm thick SmCo7 films with Mo underlayer. From 25 to 300 ℃, the Hci decreased from 281.6 to 211.2 kA/m with a temperature coefficient of-0.091%/℃, exhibiting good temperature stability.     

Magnetic property and microstructure of SmCo magnetic recording films

Cr/SmCo/Cr thin films with Sm concentration of 37.7 at.% were deposited on glass substrates by magnetron sputtering. Meas-urement of magnetic properties showed that the SmCo film possessed good magnetic anisotropy, a high coercivity of 3019 kA/m and low magnetic exchange coupling. Microstructure analysis showed that crystallized SmCo5 magnetic phase, non-magnetic SmCo2 phase and Sm2Co7 phase co-existed ill the film. The non-magnetic SmCo2 phase might function as isolator of SmCo grains, leading to a decrease of magnetic exchange coupling. Moreover, a Cr2)3 oxide layer which could protect the SmCo layer from oxidation formed at the surface of the Cr cap layer.     

Anisotropic Sm2Col7 nano-flakes produced by surfactant and magnetic field assisted high energy ball milling

Anisotropic Sm2Co17 flakes with high aspect ratio were prepared by magnetic field assisted high energy ball milling in the presence of heptane and oleic acid(OA).The thickness of flakes was only tens of nanometers.Coercivity of 3 kOe was achieved in the nano-flakes.Most interestingly,the magnetic crystalline anisotropy of Sm2Co17 flakes was improved compared to that of particles made by traditional ball milling.These anisotropic Sm2Co17 nano-flakes could be the building blocks for the future high-performance nano-composite permanent magnets with an enhanced energy product.     

Magnetic Microstructures of 2∶17 Type Sm(Co,Fe,Cu,Zr)_z Magnets Detected by Magnetic Force Microscopy

Although much current attention is focused on Nd-Fe-B magnets,2∶17type Sm-Co magnets are stilli mportant objects of research because of their higherCurie temperature and superior temperature stability.However,Smvolatilizationis a serious problemin ap-plications of Sm-Co magnets under high temperature.Recently,Chen et al[1]studied the effectiveness ofmany kinds of protection coating except Tafor prevent-ing2∶17type Sm-Co magnets fromSmvolatilization.However,sofar we have seldomread pape…     

Preparation of Nanoscale Sm2Co17 Flakes by Ball Milling in Magnetic Field

A new preparation method of Sm2Co17 nanoflakes was investigated. Hard magnetic Sm2 Co17 nanoflakes with thickness of 20-100 nm were obtained by milling in heptane and oleic acid under a magnetic field of 1.5 T for 0.5-20 h. It was shown that higher anisotropic magnetic properties would be induced by the flake-shape anisotropy when the prepared Sm2 Colt particles are milled with a magnetic field. The magnetic anisotropy of flakes after being aligned under the magnetic field of 1.5 T could be further enhanced, and the value of （BH）m was 128 kJ · m a Both anisotropy and properties are better than those of the nano-particles milled without a magnetic field.     

Application of high-temperature permanent magnets Sm（Co,Fe, Cu,Zr）z in PPM focusing system

Rare earth permanent magnets Sm（Co, Fe, Cu, Zr）z with outstanding performance and high-temperature thermal stability were fabricated. Optimized by Fe content and process, Sm（Co0.72Fe0.15Cu0.1Zr0.03）7.5 magnet with B1〉0.75 T and Hci〉1300 kA/m at 300 ℃ can be obtained. According to the performance data of Sm（Co0.72Fe0.15Cu0.1Zr0.03）7.5, the magnetic field along central axis Bz in periodic permanent magnet （PPM） focusing system was simulated using electromagnetic field analysis software Maxwell 2D/3D. The Bz exhibited typical cosine curve along central axis, and the peak value of Bz was high enough to meet the demand of PPM focusing system at room temperature even at 200±20 ℃. Additionally, a kind of simple cooling structure for PPM focusing system was designed by setting cooling pipe between polepieces. Simulated results showed that smooth cosine curve of Bz was successfully achieved with good control of the thickness of cooling pipe.     

Effect of magnetic layer thickness on magnetic properties of Ce-Fe-B thin films

The Ce_2 Fe_(14)B thin films with a notable out-of-plane c-axis texture were prepared by DC magnetron sputtering on a Ta buffer layer. The morphological and magnetic properties were investigated. The thickness of the magnetic layer had a dramatic effect on the formation of Ce_2 Fe_(14)B phase,and excellent magnetic properties(H_(ci)≈4.25 kOe, M_r/M_s≈0.81) were observed for the Ce-Fe-B film with the thickness d_m = 200 nm. The results of the hysteresis loops for Ce-Fe-B film(d_m = 200 nm) at various measured temperatures show that a decoupling between the hard and the soft phases is observed at low temperatures, which is due to the regions with quite low anisotropy provided by the a-Fe. Moreover. it is clear that significantly various magnetization behaviors between the films with d_m = 200 and 300 nm were observed with a similar trend due to the existence of the a-Fe soft phase.     

Magnetic Properties of （Sm, Tb）FeCo/Cr/TbFeCo Trilayers with Perpendicular Anisotropy

A series of （Sm, Tb）FeCo/Cr/TbFeCo trilayers with perpendicular anisotropy was prepared by RF magnetron sputtering, and the effect of Cr interlayer thickness on magnetic properties and interlayer exchange coupling was investigated. All the samples showed strong out-of-plane anisotropy but their hysteresis loops displayed two types ： singlephase and double-phase, indicating that interlayer exchange coupling and magnetic properties varied with the thickness of Cr interlayer. Both saturation field Hs and （1-Mr/Ms） curves indicated that interlayer exchange coupling oscillated between antiferromagnetic and ferromagnetic with a period of 1.6 nm, and the oscillation strength attenuated with increasing Cr interlayer thickness. After being annealed at 450℃ for 25 min, the hysteresis loops of all the samples became single-phase type and coercivity Hc decreased greatly, which could be attributed to the decrease of effective anisotropy in （Sm, TbFeCo） grains.     

Industry experiment & effect of oxidation resistance coating for steel slab

Spraying test were conducted twice before steel slabs were put into the furnace and the effects of the oxidation resistance coating were investigated and verified.By comparing the change of slab weight,rolling force of the roughing mill & finishing mill,thickness of oxide film on the surface slabs by an XL-30 SEM and acid pickling speed of slabs with and without coating,it was found that the oxidization waste in the furnace decreased by 40 percent with the use of the coating and the corresponding yield capacity could increase by 0.2 percent at least.Besides,the thickness of oxide scale film on hot rolled products was reduced by 1.44 micrometers and the acid pickling time was shortened by 6s with the coating technology,while the total rolling force of RM & FM did not changed.Furthermore,the application prospect of this technology was also discussed in this paper.     

Influence of Nanometric Ceria Coating on Oxidation Behavior of Chromium at 900 ℃

Isothermal and cyclic oxidation behaviors of chromium samples with and without nanometric CeO2 coating were studied at 900℃ in air. Scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, and high-resolution electron microscopy （HREM） were used to examine the morphology and microstructure of the oxide film. It was found that ceria coating greatly improved the oxidation resistance of Cr both in isothermal and cyclic oxidizing experiments. Acoustic emission （AE） technique was used in situ to monitor the cracking and spalling of oxide film, and AE signals were analyzed in time-domain and number-domain according to related oxide fracture model. Laser Raman spectrometer was also used to study the stress of oxide film formed on Cr with and without ceria. The improvement in oxidation resistance of chromium is believed mainly due to that ceria greatly reduced the growth speed and grain size of Cr2O3. This fine grained Cr2O3 oxide film might have better high temperature plasticity and could relieve parts of the compressive stress by means of creeping and maintained ridge character and relatively lower level of internal stress. Meanwhile, ceria application reduced the size and number of interfacial defects, remarkably enhanced the adhesive property of Cr2O3 oxide scale formed on Cr substrate.     

Magnetic Microstructures of 2:17 Type Sm(Co,Fe,Cu,Zr)z Magnets Detected by Magnetic Force Microscopy

The magnetic microstructures of 2:17 type Sm(Co,Fe,Cu,Zr)z magnets were detected by magnetic force microscopy.Comparing the microstructures of the specimens coated with and without Ta thin film before and after heat-treatment, it is found that: (a) as a protection layer, Ta coating layer about 20 nm thick can effectively restrain Sm volatilization under high temperature;(b) the stress built in the 2:17 type Sm-Co magnets during specimen preparation only affects some local parts of the domain structures;(c) the magnetic microstructures vary largely for specimens heat-treated at high temperature without Ta film coating due to Sm volatilization.In addition, by comparing with high coercivity Fe-Pt point tips, it is found that the Co-Cr thin-film tips are not suitable for detecting the magnetic microstructures of strong permanent magnets.     

Improved Electrical Insulation of Rare Earth Permanent Magnetic Materials With High Magnetic Properties

 Rare earth permanent magnetic materials are typical electrical conductor, and their magnetic properties will decrease because of the eddy current effect, so it is difficult to keep them stable for a long enough time under a high frequency AC field. In the present study, as far as rare earth permanent magnets are concerned, for the first time, rare earth permanent magnets with strong electrical insulation and high magnetic performance have been obtained through experiments, and their properties are as follows: (1) Sm2TM17: Br=062 T, jHc=8037 kA/m, (BH)m=5897 kJ/m3, ρ=7 Ω·m; (2) NdFeB: Br=0485 T, jHc=76633 kA/m, (BH)m=3796 kJ/m3, ρ=9 Ω·m. The magnetic properties of Sm2TM17 and NdFeB are obviously higher than those of ferrite permanent magnet, and the electric insulating characteristics of Sm2TM17 and NdFeB applied have in fact been approximately the same as those of ferrite. Therefore, Sm2TM17 and NdFeB will possess the ability to take the place of ferrite under a certain high frequency AC electric field.     

Magnetic Domains and Coercivity in SmCo 2:17 Type Magnets

The coercivity of SmCo 2:17-type magnets is known to be very sensitive to details of the processing procedure. In this study we have found that the same is true with respect to the domain structure of these magnets. Thus in optimally processed high temperature Sm(Co_0.784Fe_0.1Cu_0.088Zr_0.028)_7.19 magnets, the typical domain width is less than 1 μm, but significantly larger than the typical size of 2:17R cells of about 100 nm. On the other hand, quenching straight from the aging temperature of 850 °C, i.e. omitting slow cooling, leads to a much coarser domain structure (domain width ∼ 10 μm) and a small coercivity (< 0.1 T). The fine domain structure of the optimally processed bulk magnet can be considered as interaction domains - an alternative phenomenon compared to the zigzag shaped domain walls known for thinned specimen.     

Domain Structure and Magnetic Properties of Epitaxial Rare Earth-Transition Metal Thin Films

Rare Earth-Transition Metal permanent magnet films were epitaxially grown by pulsed laser deposition on heated MgO single crystal substrates of different orientations. The epitaxial growth relation of film, buffer and substrate is studied by pole figure measurements and its consequences on the anisotropic magnetic behavior are discussed. In the investigated material systems, RCo₅ (R = Sm, Pr) and Nd-Fe-B, high anisotropies and coercivities are achieved, the film morphology, domain structure and the coercivity mechanism are, however, distinctly different. The small scaled domain structure found for SmCo₅ and PrCo₅ films is a consequence of the small grain sizes and the magnetization process is dominated by strong pinning. Nd₂Fe₁₄B based films, on the other hand, are nucleation type magnets and coercivity is influenced by film morphology and roughness.     

Structure and Magnetic Properties of Sm2Fe17Nx Sintering Magnets Prepared by Spark Plasma Sintering

Bulk Sm2Fe17Nx sintering magnet was fabricated by spark plasma sintering(SPS) technique. The effects of sintering pressure and sintering temperature on the magnetic properties of the Sm2Fe17Nx magnet were investigated. As a result, the density of the magnet is obviously improved with the increase of sintering pressure, but the coercivity drops since Sm2Fe17Nx has decomposed into SmN, α-Fe and N2. When sintering temperature was only above 200 ℃ under 1 GPa sintering pressure, the coercivity even begins to decrease, which indicates that high pressure promotes the decomposition of the Sm2Fe17Nx at lower temperature. The decomposition is also proved by the decrease of nitrogen and increase of α-Fe in the magnets.     

Spark Plasma Sintering Bulk Sm2 Fe17NxMagnets

High performance Sm2Fe17Nx magnetic powders were fabricated by ball-milling method and were compacted using spark plasma sintering(SPS) technique.Effects of processing conditions on the magnetic properties and decomposition dynamic of the magnets were investigated.It is found that higher sintering temperature improves the densification of the magnets, while deteriorates their magnetic properties simultaneously due to the decomposition of the Sm2Fe17Nx.Sintering at lower temperature can preserve the crystal structure of Sm2Fe17Nx compound, while the powders cannot be consolidated into a fully dense compact.An increased compressive pressure leads to better magnetic properties and higher density for the magnet at the same sintering temperature.     

Magnetic susceptibility of Al2RE compounds in crystal and liquid states

Magnetic susceptibility of Al2RE (RE=Y, Ce, Sm, Gd, Dy, Ho, Yb) compounds was studied experimentally in wide temperature (T=290-2000 K) and field (B=0.3-1.3 T) intervals. The abnormal increase in susceptibility beginning above the melting point was fixed for all the compositions. The values for the effective magnetic moments per RE atoms in these compounds were found to be smaller than the values typical for free ions RE3+. The results were discussed in supposition of the directed bonds between aluminum and rare-earth atoms.     

Preparation and magnetic properties of anisotropic Nd_2Fe_(14)B/Sm_2Co_(17) hybrid-bonded magnets

In the present work, anisotropic Nd_2 Fe_(14) B/Sm_2 Co_(17) hybrid-bonded magnets were prepared with different Nd-Fe-B contents. It is found that the particle distributions and ratios between the two magnetic phases have important roles in the magnetic properties, microstructures and thermal stability of the magnets. With increase of Nd-Fe-B content, the saturation magnetization of the anisotropic hybrid magnet increases significantly, however, coercivity decreases, and the demagnetization curves show magnetically single-phase behavior. The anisotropic Nd_2 Fe_(14) B/Sm_2 Co_(17) hybrid-bonded magnets exhibit a maximum energy product and remanence of 14.15 MGOe and 99.53 A·m~2/kg, respectively, when the NdFe-B content is 70 wt% at room temperature. Furthermore, the hybrid magnets also have better thermal stability at elevated temperatures due to the interaction between the two magnetic particles.     

Model for Calculating J(H) Curves of Ni Coated Nd-Fe-B Magnets

An analytical model to describe the influence of surface degradation and the Ni layer itself on the magnetic properties of Ni coated Nd-Fe-B magnets is presented. Starting from the bulk magnetic properties, the dimensions, the thickness of Ni coating and the affected surface layer, J(H) demagnetization curve is calculated. Subsequently the expected values of (BH)_max, and the reversible permeability are deduced from the calculated J(H) curves. For flat magnets the surface effects lead to a decrease of B_r and an increase of the permeability which lowers (BH)_max. For strait magnets a step in the J(H) curve appears at H = 0. The deteriorating effect of Ni coating and the surface layer scale with the dimensions of magnet and the thickness of these layers, which depend on the processing and the grain size of magnet. These effects can not be neglected if one or more dimensions of a Ni coated magnet are less than about 5 mm. SmCo₅ magnets show similar effects but the coercivity of the damaged surface layer is higher. Pinning type Sm₂Co₁₇ magnets show almost no deterioration on surface due to machining. As a result, Sm-Co magnets are better suited for applications with dimensions smaller than about 2 mm.