SmCo Magnets Research Articles

Effect of quench rate on nanostructure and magnetic properties of PrCo5

The effect of quench rate on nanostructure and magnetic properties of PrCo5 alloy has been investigated. The increase of quench rate through wheel speed in melt spinning suppresses the formation of the secondary Pr2Co17 and Pr5Co19 phases with low magnetocrystalline anisotropy field and refines the nanostructure. This significantly improves the coercivity, remanence, and energy product. For example, increasing the wheel speed from 30 m/s to 70 m/s increases the coercivity and energy product from 3.2 kOe and 4.0 MGOe to 10.3 kOe and 13.7 MGOe, respectively. The magnetic hardening mechanism appears to be a mixture of reversed-domain-nucleation and domain-wall-pinning. The temperature coefficient of coercivity for the 70 m/s sample is −0.16%/K from 300 to 700 K, which is better than that of sintered SmCo5 magnets. Low temperature coefficients of coercivity and remanence indicate that rapidly quenched PrCo5 ribbons may be suitable for bonded magnets with high operation temperature.

Hard-phase engineering in hard/soft nanocomposite magnets

Bulk SmCo/Fe(Co) based hard/soft nanocomposite magnets with different hard phases (1:5, 2:17, 2:7 and 1:3 types) were fabricated by high-energy ball-milling followed by a warm compaction process. Microstructural studies revealed a homogeneous distribution of bcc-Fe(Co) phase in the matrix of hard magnetic Sm-Co phase with grain size ⩽20 nm after severe plastic deformation and compaction. The small grain size leads to effective inter-phase exchange coupling as shown by the single-phase-like demagnetization behavior with enhanced remanence and energy product. Among the different hard phases investigated, it was found that the Sm2Co7-based nanocomposites can incorporate a higher soft phase content, and thus a larger reduction in rare-earth content compared with the 2:17, 1:5 and 1:3 phase-based nanocomposite with similar properties. (BH)max up to 17.6 MGOe was obtained for isotropic Sm2Co7/FeCo nanocomposite magnets with 40 wt% of the soft phase which is about 300% higher than the single-phase counterpart prepared under the same conditions. The results show that hard-phase engineering in nanocomposite magnets is an alternative approach to fabrication of high-strength nanocomposite magnets with reduced rare-earth content.

Evolution and effects of surface degradation layer of Sm2Co17 magnets at high temperatures

The long-term application of SmCo-based magnets at high temperatures has been restricted by the irreversible loss of magnetic properties. In this work, degradation behavior of Sm2Co17 magnets was studied at 500 °C in air and vacuum by being focused on the surface degradation layer. The structure and the composition of the degradation layer were studied experimentally, and the magnetization was calculated to certify the deduction of the irreversible loss. The soft magnetic phases in the degradation layer can result in the decline of the magnetization and the irreversible loss of magnetic properties. Furthermore, the controversial formation reason of the degradation layer was also studied. It was found that the diffusion of the oxygen, but not the sublimation of Sm, could be the dominant formation reason of the degradation layers.

Sm-Co磁石の組織形成に対するフェーズフィールド解析とイメージベース磁気特性計算

Sm-Co磁石の組織形成に対するフェーズフィールド解析とイメージベース磁気特性計算

Low fragment polyatomic molecular ion source by using permanent magnets

Electron-ionization-type polyatomic molecular ion source with low fragment was developed by using a pair of ring-shaped Sm-Co magnets. The magnets were placed forward and backward side of ionization part to confine electrons extracted from a thermionic cathode. Calculated electron trajectory of the developed ion source was 20 times longer than that of an ordinary outer filament configuration that has no magnetic confinement. Mass spectra of the molecular ions generated from n-tetradecane(C14H30) gas exhibited 4 times larger intensity than that of the ordinary configuration in a range of mass/charge from 93 to 210 u. This indicates that suppression of fragment ion was obtained by increase of low energy electrons resulted from the electron confinement.

Recent progress in high temperature permanent magnetic materials

Permanent magnetic materials capable of operating at high temperature up to 500 °C have wide potential applications in fields such as aeronautics, space, and electronic cars. SmCo alloys are candidates for high temperature applications, since they have large magnetocrystalline anisotropy field (6–30 T), high Curie temperature (720–920 °C), and large energy product (>200 kJ·m−3) at room temperature. However, the highest service temperature of commercial 2:17 type SmCo magnets is only 300 °C, and many efforts have been devoted to develop novel high temperature permanent magnets. This review focuses on the development of three kinds of SmCo based magnets: 2:17 type SmCo magnets, nanocrystalline SmCo magnets, and nanocomposite SmCo magnets. The oxidation protection, including alloying and surface modification, of high temperature permanent magnets is discussed as well.

Experimental research on the residual magnetization of a rare-earth permanent magnet for a cryogenic undulator

The magnetic properties of commercial polycrystalline Nd2Fe14B (N50M, N45H, N40SH, N35EH) and Sm2Co17 (XG30/20, XG26/25, XG22/20) magnets at cryogenic temperatures were tested by using a comprehensive physical properties measurement system (PPMS). The results show that the spin tilt temperature Tst of Nd2Fe14B magnets is closely related to intrinsic coercivity Hci, N50M and N45H with smaller Hci show a residual magnetization jump at 235 K and 225 K, respectively. For Sm2Co17 magnets, in 50–300 K, with temperature decreasing, residual magnetization Mrc shows a nearly linear increase, while in 10–50 K, Mrc has little change. The research results provide a reference for cryogenic undulators and other high-precision cryogenic devices.

Investigation of Magnetic Behavior of SmCo<sub>5</sub>/SmCo<sub>2</sub> Nanocrystalline Magnets

Nanocrystalline magnets (SmCo5)94(Cr3C2)6 were prepared using melt-spinning and their magnetic behaviors were investigated by studying their structures and magnetic properties. The alloys prepared using rapid solidification consisted of SmCo5 matrix phase, MgCu2-type SmCo2 secondary phase, and small traces of Sm2Co7 phase. The solidification with higher wheel speed were found to be preferable for the formation of single SmCo2 secondary phase. Relatively high coercive values of 28–36 kOe and high reduced remanence of 0.78–0.79 were observed for the SmCo5/SmCo2 nanocrystalline magnets. The shape of the corresponding magnetization curves revealed that two magnetization processes, nucleation and pinning of domain walls, took place in these magnets. The Henkel plots indicated strong inter-grain exchange coupling effect in these ribbons, consequently resulted in the phenomena of domains interacting with each other and enhancement of the remanence in the ribbons.

Magnetic Hysteresis and Electrical Impedance Spectra of Hard Magnetic SmCo5 and Soft Magnetic Co30Ag70 Composites

Abstract A Vibrating Sample Magnetometer (VSM) and a set-up for electrical impedance measurement in magnetic field were employed to study Co 30 Ag 70 mechanical alloys with additions of 0%, 5% and 10% (mass fraction) hard magnetic SmCo 5 . With increasing SmCo 5 content, the particulate composites exhibited an increase in the remanent magnetization when the coercive field remained rather constant. The electrical impedance of each composite did not show a large variation between 10 kHz and 100 kHz but rapidly rose with the increase in frequency from around 200 kHz to 1 MHz due to the skin effect. All impedance spectra were slightly shifted when the magnetic field of 3.3 kA/m was applied. The largest difference was observed in the case of Co 30 Ag 70 without SmCo 5 addition. The results confirmed the relationship between the magnetic softness of materials and their electrical impedance in magnetic field.

Fully Epitaxial, Exchange Coupled SmCo$_{5}$/Fe Multilayers With Energy Densities above 400 kJ/m$^{3}$

Exchange coupled hard/soft magnetic nanocomposites have long been in the interest of research for improving the energy density of the currently best hard magnetic materials such as Nd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sub> B (512 kJ/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ) or SmCo <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> (230 kJ/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ). However, to compete with the energy density of a well textured single phase bulk magnet, the hard magnetic phase within the two-phase material should be sufficiently textured as well. Thus, only recently values of more than 300 kJ/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , i.e., significantly above the theoretical hard phase limit of SmCo <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> , have been realized in fully epitaxial SmCo <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> /Fe/SmCo <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> trilayers. Here we extend our work to fully epitaxial SmCo <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> /Fe multilayers with reduced individual layer thicknesses of Fe and SmCo <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> . The rigid coupling of a large volume fraction of high moment soft phase to a hard magnetic Sm-Co phase leads to energy densities above 400 kJ/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . Phase formation, epitaxial texture and magnetic properties are discussed for a series of multilayers of constant total thickness with respect to the number of introduced interfaces.

Effect of ball-milling surfactants on the interface chemistry in hot-compacted SmCo5 magnets

Anisotropic SmCo5 nanoflakes prepared by high-energy ball-milling with surfactants have great potential in applications for high-performance nanocomposite magnets. For such “nanocomposite” applications, the surface structure and chemistry of nanoflakes are crucial for achieving high coercivity. In this study, hot-pressed samples from anisotropic SmCo5 nanoflakes, ball-milled with different surfactants, oleic acid (OA) and oleylamine (OY), were investigated. Interface layers between the SmCo5 nanoflakes were found to consist of samarium oxides and a soft magnetic Co phase. These surface layers contribute to the degradation of hard magnetic performance, which is confirmed by scanning transmission electron microscopy-energy dispersive X-ray spectroscopy analysis of the cross-section of a single flake ball-milled with OA. Samples milled with OY show a much thinner interface layer in compacted samples, which means that the surface degradation during ball-milling with OY is much less than that with OA. The results show clearly that the choice of proper surfactant and the control of processing parameters are the key factors for improving the surface condition of the nanoflakes and the resulting hard magnetic properties.

Sm2Co17系磁石の現状と将来展望

Sm2Co17 magnets have high thermal resistivity and corrosion resistance with over 240 kJ/m3 of (BH)max, which are well balanced ones. But as NdFeB magnets are superior to both magnetic properties and costs, the Sm2Co17 magnets are used in severe circumstance such as automobile applications. The magnetic property of Sm2Co17 magnets are reviewed at first and its coercive force mechanism is discussed. As follow, some applications are introduced.

STUDY ON SmCo PERMANENT MAGNETS UNDER 350 MODERATE TEMPERATURES

The magnetic properties of commercial 2:17-type SmCo magnet are low at high temperature,despite good properties at room temperature,therefore its application temperature is usually lower than 300℃.In recent years,significant progress has been made on the development of SmCo permanent magnets for high temperature applications.Despite the maximum operating temperature being up to 500℃.the magnets were found to have low magnetic properties at room temperature and 350℃.Thus,there is a demand for developing permanent magnet materials with high properties at moderate temperatures below 350℃.The effect of Fe and Cu contents on the magnetic properties of Sm(Co_(bal)Fe_xCu_yZr_(0.03))_(7.5)(x=0.16—0.28,y=0.06.0.08) magnets at room temperature and 350℃have been systematically studied.The results show that with increasing Fe content,the intrinsic coercivity _iH_c gradually increases,reaching an optimal value of 2473 kA/m,and then drops rapidly at room temperature;the remanence B_r rises monotonically with increasing Fe content.The intrinsic coercivity _iH_c increases with raising Cu at a constant Fe content.The absolute value of temperature coefficient of coercivity |β| rises monotonically with increasing Fe content,and decreases with increasing Cu content.Sm(Co_(bal)Fe_(0.20)Cu_(0.08)Zr_(0.03))_(7.5) alloy is expected for potential applications at moderate temperatures below 350℃.

Influences of Permanent Magnets Temperature Characteristic on the Levitation Force of YBaCuO Bulk Superconductors

Influences of the temperature characteristic of sintered SmCo and NdFeB permanent magnets (PM) on the levitation force of YBaCuO bulk superconductor have been investigated in this paper. It is found that for a NbFeB PM and a SmCo PM which have the same geometric parameters, a larger influence on the levitation force of a temperature decrease of the NdFeB PM has been found. The maximum change of levitation force is as high as 47.6% at a gap of 2 mm between the bottom surface of NdFeB PM and the top surface of YBaCuO bulk when the temperature of the NdFeB PM decreases from room temperature to 77 K. This work provides basic data for high temperature superconducting levitation system measurements.

Effect of Sm-rich liquid phase on magnetic properties and microstructures of sintered 2:17-type Sm-Co magnet

The effect of Sm-rich liquid phase (Sm 2Co 3) on magnetic properties and microstructure of 2:17-type Sm-Co magnet was studied. Three phases existed in liquid phase ingot, and took on white, dark grey and grey, respectively. It was found that the composition of the grey area was similar to the nominal one. Our results indicated that the optimal composition was obtained at 3 wt.% liquid phase added, and the magnetic properties were B r=11.58 kGs, H ci >26 kOe, ( BH) m=29.51 MGOe. B r increased by 3%, H ci was 13 times larger, and ( BH) m was 6 times bigger than none liquid phase magnets. Moreover, with the aging time decreasing from 20 to 8 h, the squareness of the demagnetization curves got better, while the coercivity of the samples decreased. It revealed that Sm(Co, Cu) 5 phase also precipitated at particle boundaries. It maybe also enhanced the coercivity.

Self-nanoscaling of the soft magnetic phase in bulk SmCo/Fe nanocomposite magnets

Fabrication of bulk nanocomposite materials, which contain a magnetically hard phase and a magnetically soft phase with desired nanoscale morphology and composition distribution has proven to be challenging. Here we demonstrate that SmCo/Fe(Co) hard/soft nanocomposite materials can be produced by distributing the soft magnetic α-Fe(Co) phase particles homogenously in a hard magnetic SmCo phase matrix through a combination of high-energy ball milling and a warm compaction. Severe plastic deformation during the ball milling results in nanoscaling of the soft phase with size reduction from micrometers to ~15 nm. Up to 35% of the soft phase can be incorporated into the composites without coarsening. This process produces fully dense bulk isotropic nanocomposite materials with remarkable energy-product enhancement (up to 300%) owing to effective inter-phase exchange coupling.

Using deep eutectic solvents to electrodeposit CoSm films and nanowires

A Deep Eutectic Solvent of 1 chlorine chloride: 2 urea eutectic mixture at 70 °C has been tested as useful to electrodeposit both magnetic SmCo films and nanowires. Galvanostatic deposition allows obtaining homogeneous deposits over metallic substrate with variable composition as a function of the current density applied. The deposits obtained at 0.5–1.5 mA cm − 2 were uniform and they correspond to a cobalt hexagonal crystalline phase with magnetic anisotropy and coercivity of 250 Oe. It has been possible to deposit SmCo nanowires from the DES solvent using alumina templates. Uniform CoSm nanowires of 50 nm of diameter have been obtained; they correspond also to hexagonal phase, but they present higher coercivity.

Testing the intrinsic noise of a coil–magnet actuator for cryogenic gravitational wave interferometers

The third generation gravitational wave interferometers that will operate underground and at cryogenic temperatures will need a complex and sophisticated control system to satisfy the requirements on the alignment and position of its optics and keep the detector at its working point. The force actuators of the control systems of the present interferometers are for the most part coil–magnet actuators. To check the possibility of using these actuators also at low temperature we have tested the magnetization and the magnetization noise of an SmCo magnet at 4.2 K. The magnetization loss, measured with a fluxgate magnetometer, is 7%. The magnetization noise has been measured with a superconducting quantum interference device magnetometer. The application of dc and ac (0.1 Hz) magnetic fields of an amplitude comparable to that needed to produce on the magnet a force large enough for the control system does not change the measured noise. The equivalent maximum force noise produced by the actuator as a result of the magnetization noise of the magnet has been evaluated. Its effect on the sensitivity of a third generation interferometer (Einstein Telescope) is negligible with respect to the most relevant fundamental noise contributions.

Influence of the type of surfactant and hot compaction on the magnetic properties of SmCo5 nanoflakes

In this study, we discuss the effects of a type of surfactant (oleylamine, oleic acid, and trioctylamine) and hot pressing on the hard magnetic properties of crystallographically anisotropic SmCo5 nanoflakes prepared by surfactant-assisted high energy ball milling. The phase, microstructure, and magnetic properties of the hot-pressed SmCo5 were investigated by using x-ray diffraction, scanning electron microscopy, and vibrating sample magnetometry. The coercivities of the precursor flakes prepared using oleylamine, oleic acid, and trioctylamine were 14.9, 15.8, and 15 kOe, respectively. Hot-compacted SmCo5 magnets prepared from the nanoflakes milled with oleic acid had the lowest coercivity of 8.1 kOe. It is believed that even after repeated washing in an ultrasonic bath with different solvents, the remaining oleic acid in the SmCo5 nanoflakes led to oxidation of SmCo5 at the surface/interface of nanoflakes during the hot-pressing process. The compacted SmCo5 magnets prepared from the nanoflakes milled with trioctylamine and oleylamine had higher coercivity values of 14.8 and 12.8 kOe, respectively. Unlike oleic acid, oleylamine and trioctylamine contain no oxygen atoms, and therefore there was less oxidation during the process. The compaction temperature also influences the coercivity. The SmCo5 magnets hot pressed at 550 °C had the highest coercivity, whereas those hot pressed at 650 °C had the lowest coercivity; this is attributed to the change of phases and composition of SmCo5 alloys during the hot-pressing process.

Investigation on microstructure and magnetic properties of Sm2Co17 magnets aged at high temperature

The Sm2Co17 magnet is the most promising candidate for high temperature applications. The microstructure evolutions and losses in the magnetic properties of the magnet in high temperature aging status have been investigated. The Sm(CobalFe0.22Cu0.068Zr0.025)7.75 magnets were prepared using the conventional powder sintering method. The magnet samples were isothermally aged at 500°C, 600 °C, and 700 °C for 72 h, respectively. The magnetic properties and the demagnetization curve were kept invariable for the magnet samples aged at 500 °C. The coercivity Hcj of the magnet samples decreased with increasing aging temperature. The Hcj decreased from 29.2 kOe for the original status samples to 10.8 kOe for the samples aged at 700 °C. The cell structure in the magnet is not destroyed after aging at 700 °C for 72 h. The deterioration of the magnetic properties and the demagnetization-curve squareness was caused by an increasing lattice mismatch between the 2:17R cell phase and the cell-boundary 1:5H phase, and by an increasing cell diameter for the magnet sample aged at a high temperature.