Advance in the chemical synthesis and magnetic properties of nanostructured rare-earth-based permanent magnets

Rare-earth-based permanent magnets are one of the most important magnets in both scientific and industrial fields. With the development of technology, nanostructured rarearth-based permanent magnets with high energy products are highly required. In this article, we will review the progress in chemical synthetic strategies of nanostructured rare-earth-based permanent magnets.

Design and Optimization of Line-Start Rare-Earth Permanent Magnetic Synchronous Motor Basing on FEM

The 2D transient FEM was used to analyze the starting process of the three phase rare-earth LS-PMSM.By verifying the simulation result with the experiment one, we get the conclusion that it is consistent with the experiment result very well.At the same time, by analyzing the situation of the magnetic bridge, we also get the result that the amplitude of EMF waves are changing with the situation of the magnetic poles and we can optimize the motor's structure at the same time.

Computational Design of Rare-Earth Reduced Permanent Magnets

Multiscale simulation is a key research tool in the quest for new permanent magnets.Starting with first principles methods,a sequence of simulation methods can be applied to calculate the maximum possible coercive field and expected energy density product of a magnet made from a novel magnetic material composition.Iron(Fe)-rich magnetic phases suitable for permanent magnets can be found by means of adaptive genetic algorithms.The intrinsic properties computed by ab initio simulations are used as input for micromagnetic simulations of the hysteresis properties of permanent magnets with a realistic structure.Using machine learning techniques,the magnet’s structure can be optimized so that the upper limits for coercivity and energy density product for a given phase can be estimated.Structure property relations of synthetic permanent magnets were computed for several candidate hard magnetic phases.The following pairs(coercive field(T),energy density product(kJ·m^-3))were obtained for iron-tin-antimony(Fe3Sn0.75Sb0.25):(0.49,290),L10-ordered iron-nickel(L10 FeNi):(1,400),cobalt-iron-tantalum(CoFe6Ta):(0.87,425),and manganese-aluminum(MnAl):(0.53,80).

Effects of spacer layers on magnetic properties and exchange couplings of Nd-Fe-B/Nd-Ce-Fe-B multilayer films

The influences of the spacer-layer Ta on the structures and magnetic properties of NdFeB/NdCeFeB multilayer films are investigated via DC sputtering under an Ar pressure of 1.2 Pa. An obvious （00l） texture of the hard phase is observed in each of the films, which indicates that the main phase of the film does not significantly change with Ta spacer-layer thickness. As a result, both the remanence and the saturation magnetization of the magnet first increase and then decrease, and the maximum values of 4π Mr and Hcj are 10.4 kGs （1 Gs=10^-4 T） and 15.0 kOe （1 Oe=79.5775 A·m^-1） for the film with a 2-nm-thick Ta spacer-layer, respectively, where the crystalline structures are columnar shape particles. The measured relationship between irreversible portion D （H）=-△ Mirr/2Mr and H indicates that the nucleation field of the film decreases with spacer layer thickness increasing, owing to slightly disordered grains near the interface between different magnetic layers.

INFLUENCES OF NEODYMIUM ON MAGNETIC CHARACTERISTICS OF ELECTROPLATING CoNdNiMnP FILMS

In order to improve the performances of electroplating permanent magnetic films, neodymium is introduced into the electroplating CoNiMnP permanent magnetic films. The influences of the neodymium content are also investigated by varying NdCl3 plating bath concentration. The neodymium-doped films are analyzed by energy dispersive spectrum (EDS), vibrating sample magnetometer (VSM) and magnetic force microscope (MFM). The experimental results show that high magnetic performances of CoNdNiMnP permanent magnetic films with vertical anisotropy could be fabricated with current density 5mA/cm2 at room temperature. With the increasing of neodymium contents, the magnetic properties of films were improved. However when neodymium contents exceeded 3.5wt%, the magnetic properties of films are not improved any more. The increase of film magnetic properties results from the ferromagnetic-coupling between light rare earth element-neodymium and transition metal element-cobalt.

Permanent Rare-Earth Magnets—The Need to Protect Them against Corrosion

The RE-Fe-B permanent magnets have a complex microstructure and they are susceptible to corrosion process. In this paper, the commercial nickel coatings adhesion was investigated. The microstructure of the RE-Fe-B without coating was analyzed by scanning electronic microscopy and electrochemical techniques. The interface magnet/coating was studied by scanning electron microscopy and the nickel-plated Nd-Fe-B commercial magnets were tested in a salt spray chamber. The ferromagnetic and RE-rich phases were observed. After the anodic polarization curve, a strong intergranular corrosion was observed and the RE-rich phase was preferentially attacked. The interface magnet/Ni coating presented inter-granular corrosion that can affect the nickel coating adherence. This attack had probably occurred during the electrodeposition process. Not all the samples suffered localized corrosion during the salt spray tests and the Ni triple-layer coating presented a few corrosion points. RE-Fe-B alloy magnets need to be protected with appropriate coatings to each environment to which they will be exposed and the protective coating must not be damaged.

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.

Structure and Magnetic Properties of LaCo_(13-X)M_X Intermetallic Compounds

LaCo_(13) has the highest 3d metal content ,of any known rare-earth intermetallic compounds,a1. 03MA/m saturation magnetization at room temperature and a high T_c (1318K). Unfortunately ,it is cubic ,lacking of the necessary anisotropy,thus diminishing the chance that it will be used as a permanent rnagneticmaterial. In this paper ,the structure and magnetic properties of LaCo_(13) Six (x=2 , 4 )and LaCo_(13) Ge_X(x=2,2. 5 ,3 ,4)intermetallic compounds have been studied. The crystal structure was found to be tetragonal whenx=4 for LaCo_(13-X) Six and x=3 , 4 for LaCo_(13-X) Gex ,but the difference between the lattice parameters a and c isvery small. In order to gain the tetragonal structure ,the annealing temperature of LaCo_(13-X) Ge_X must be con-trolled strictly. The magnetic rneasurement results show that the Curie temperatures of all these compoundsare high ,but the saturation magnetization at room-temperature decreases greatly with x increasing.

Magnetic properties of gadolinium and/or dysprosium substituted Sm-Co nanocomposite ribbons

The present study reported the influence of heavy rare-earth elements(Gd and/or Dy)on Sm-Co-based melt-spun ribbons.Microstructure and magnetic properties of Sm-Co-based(Sm_(1-x)RE_(x)Co_(5))ternary and quaternary systems were investigated.The X-ray diffraction,Auger spectroscopy,scanning electron microscopy(SEM)and transmission electron microscopy(TEM)analyses reveal the presence of the 1:5H and 2:17R phases in the as-spun ribbons.A high-temperature magnetic measurement reports a Curie temperature(Tc)at~825 and~869 K in Sm0.6Gd0.4Co5(ribbon A)and Sm_(0.6)Gd_(0.3)Dy_(0.1)Co_(5)(ribbon B),respectively.A low-temperature magnetic measurement on Sm0.6Gd0.3Dy0.1Co5 ribbons exhibits a type-2 SR(spin reorientation)behaviour at~72 K,which arises due to the presence of the DyCo5 phase.Room temperature magnetic measurements reveal that overall magnetic measurement(OMP)is about 24 and 29.9 for ribbons A and B,respectively.Consequently,the comparative investigations profess that ribbon B shows better magnetic performance due to Dy addition with reduced grain size.This observation indicates that the Gd and Dy substituted Sm-Co magnet can be a potential magnet for high-temperature applications.

基于滑膜观测器的永磁同步电机控制研究

文章以船舶推进永磁同步电机((Permanent Magnet Synchronous Motor,PMSM))为基础,提出了一种改进的滑模观测器,来优化PMSM调速系统控制。传统滑模观测器在反电动势估算时会产生相抖振问题,因此采用新的饱和函数作为开关函数,设计了自适应滑模增益,来提高观测器的稳定性。针对低通滤波器动作时,系统易发生相位延迟,设计了动态截止频率低通滤波器,并与Kalman滤波器结合进一步改善了系统性能。最后,结合Matlab模拟电机的控制系统,验证改良的无传感器控制系统估算的有效性及优越性。

Corrosion Resistance of Sintered NdFeB Permanent Magnet With Ni-P/TiO_2 Composite Film

The Ni-P/TiO2 composite film on sintered NdFeB permanent magnet was investigated by X-ray diffraction （XRD）,environmental scanning electron microscopy （ESEM）,and energy dispersive X-ray spectrometer （EDX）. The corrosion resistance of Ni-P/TiO2 film coated on NdFeB magnet,in 0.5 mol/L NaCl solution,was studied by potentiodynamic polarization,salt spray test and electrochemical impedance spectroscopy （EIS） techniques. The self-corrosion current density （icorr） and the polarization resistance （Rp） of Ni-P/TiO2 film are 0.22 μA/cm2 （about 14% of that of Ni-P coating）,and 120 kΩ·cm2 （about 2 times of that of Ni-P coating）,respectively. The anti-salt spray time of Ni-P/TiO2 film is about 2.5 times of that of the Ni-P coating. The results indicate that Ni-P/TiO2 film has a better corrosion resistance than Ni-P coating,and the composite film increases the corrosion resistance of NdFeB magnet markedly.

Development of samarium–cobalt rare earth permanent magnetic materials

Samarium–cobalt rare-earth（Sm–Co-RE） permanent magnetic materials with large magnetic energy product, high coercive force, high Curie temperature, good thermal stability, and corrosion resistance, have wide potential applications in aerospace, microwave communications, instrumentation, electrical engineering, magnetic machinery, etc. In this paper, the development of Sm–CoRE permanent magnetic materials in the following aspects in recent years was summarized： Sm–Co-RE permanent magnets with high application temperatures, positive temperature coefficients of coercive force, zero temperature coefficients of residual magnetization, high resistance rate,high mechanical property, and nanocrystallization.

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

The Ce;Fe;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;Fe;B phase,and excellent magnetic properties(H;≈4.25 kOe, M;/M;≈0.81) were observed for the Ce-Fe-B film with the thickness d;= 200 nm. The results of the hysteresis loops for Ce-Fe-B film（d;= 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;= 200 and 300 nm were observed with a similar trend due to the existence of the a-Fe soft phase.

Effect of film thickness on magnetic properties of Cr/SmCo/Cr films

Cr/SmCo/Cr films with different SmCo thickness were deposited on glass substrates by magnetron sputtering,followed by an annealing process at 550 °C for 20 min.Experimental results showed that the SmCo film of 30 nm exhibited two-phase behavior in the demagnetization process,the obvious kink was observed near zero.For the SmCo film of 50 nm,the kink was invisible,and a single phase like behavior was obtained in the demagnetization process.The reversal behavior became consistent in the thicker films.Moreover,the coercivity reduced and the saturated magnetization increased obviously with the increasing thickness.X-ray diffraction results indicated that the average grain size of SmCo 5 in the thicker films were almost 30 nm,but the quantity of SmCo 5 grains increased with the increasing thickness,which enhanced the intergrain exchange coupling（IEC） of the SmCo 5 hard phases.The increase of IEC improved the magnetic properties of SmCo films with increasing thickness.

A NEW TYPE OF RARE-EARTH IRON PERMANENT MAGNET——BONDED Sm_2Fe_(17)N_y MAGNET

It is well known that the permanent magnet materials are widely used in industry, medical treatment and daily life. Since the discovery of Sm-Co rare-earth transition-metal magnets, the researchers on magnetic materials have made great efforts trying to substitute Co by Fe so as to obtain Fe-based rare-earth permanent magnet materials with low cost. The success in producing Nd2Fe14B permanent magnet has given a new impetus to the study on ironrich rare-earth alloys.

Hydrogen Embrittlement Processes and Al/Al_2O_3 Hydrogen Resistance Coatings of NdFeB Magnets

After analyzing the phenomena and processes of hydrogen embrittlement of NdFeB permanent magnets, RF magnetron sputtering was used to fabricate Al thin films and then oxidized to form the Al/Al_2O_3 composite films on the magnets as the hydrogen resistance coatings. SEM and EDS were used to examine the morphology and composition respectively. Hydrogen resistance performance was tested by exposing the magnets in 10 MPa hydrogen gas at room temperature. The results show that the magnets with 8 μm Al/Al_2O_3 coatings can withstand hydrogen of 10 MPa for 65 min without being embrittled into powder. The samples with and without hydrogen resistance coatings have almost the same magnetic properties.

1∶12型稀土铁基永磁材料研究进展

作为下一代稀土永磁的候选材料,1:12型稀土铁基永磁合金(RFe_(12),R=Sm,Nd)具有高内禀磁性、优异的温度稳定性及较少的稀土含量,目前受到了广泛的关注。综述了1:12型稀土铁基永磁材料最新的研究进展,详细介绍了1:12相的晶体结构及多原子取代体系的内禀磁性及技术磁性,总结了不同类型的1:12型稀土铁基永磁材料研制的技术特点及成果,并提出了后续研究中需解决的关键问题及研究方向。

Explosion Sintered Sm_2Fe_(17)N_y Permanent Magnet

Since the discovery of R2Fe17Ny by Coey and Sun Hong, the intrinsic and extrinsic magnetic properties of these nitrides have been extensively investigated. Having very good intrinsic magnetic properties with Curie temperature of 749 K and room temperature anisotropy field of 14 T superior to Nd2Fe14B, and room temperature saturation magnetization of 1.5 T, the Sm2Fe17Ny nitride is expected to become new permanent magnet for application. The Sm2Fe17Ny nitride with intrinsic coercivity of 3T has been obtained by mechanical alloying. The Sm2Fe17Ny, magnets bonded by metal zinc have intrinsic coercivity μ0iHc over 0.5 T and magnetic product （BH）maxabout 80 kJ·m-3

NdFeB永磁体表面磁控溅射铝防护镀层性能研究

目的研究一种NdFeB永磁体表面腐蚀防护技术。方法采用磁控溅射技术,在烧结NdFeB永磁体表面沉积一层纯铝防护薄膜,然后对纯铝薄膜进行阿洛丁化学转化复合处理,表征膜层的表面和截面形貌,并研究结构及耐腐蚀性能。结果沉积的Al中间层和Al薄膜均结构致密,膜/基界面平整,膜层的自腐蚀电流密度为3.5×10-6A/cm2,说明纯Al薄膜能够对NdFeB永磁体提供有效的防护。阿洛丁化学转化可使铝薄膜表面更加致密,自腐蚀电流密度低至7.9×10-7A/cm2,进一步提高了纯铝薄膜的防护性能。结论 NdFeB永磁体表面磁控溅射镀铝是一种有效且环保的防护技术,可用于替代不环保的电镀防护。

纳米多层永磁膜α—Fe/Nd_2Fe_(14)B的成核场的微磁学计算

利用微磁学理论和变分原理，计算了纳米双相交换耦合多层膜α-Fe／Nd2Fe14B永磁体的成核场随两相磁层厚度的变化曲线。计算结果表明，当软磁相或硬磁相的厚度为某一临界值时，该交换耦合多层永磁膜的成核场达到其最大值，这与Rave等人的有限元法计算结果趋势是一致的，考虑到工艺参数的影响后，也与Shindo等人的实验及理论估算结果是一致的．