Nanocomposite Permanent Magnets Research Articles

The magnetic properties of MMCo5 (MM=Mischmetal) nanoflakes prepared by multistep (three steps) surfactant-assisted ball milling

The hard magnetic MMCo5 nanoflakes with high coercivity and narrow size distribution have been successfully obtained by three steps surfactant-assisted ball milling (SABM). The magnetic properties, phase structure and morphology of these MMCo5 nanoflakes were studied in this work. The coercivity and the remanence ratio of MMCo5 nanoflakes reached to 5.89 kOe and 0.75, respectively. The X-ray powder diffraction (XRD) patterns indicated that the MMCo5 nanoflakes were CaCu5-type hexagonal crystal structure. The average thickness, in-plane size and aspect ratio reached to 20 nm, 0.9 μm and 60, respectively. The low cost and great properties of MMCo5 nanoflakes with a centralized thickness distribution could be the building blocks for the future high-performance nanocomposite permanent magnets with an enhanced energy product.

Micromagnetic simulation of the influence of grain boundary on cerium substituted Nd-Fe-B magnets

A three-dimensional finite element model was performed to study the magnetization reversal of (CexNd1-x)2Fe14B nanocomposite permanent magnets. The influences of volume fraction, width and performance parameters of the grain boundary (GB) composition on the coercivity were analyzed by the method of micromagnetic simulation. The calculation results indicate that the structure and chemistry of GB phase play important roles in Nd2Fe14B-based magnets. An abnormal increase in the value of coercivity is found to be connected with the GB phase, approximately when the percentage of doped cerium is between 20% and 30%. While the coercivity decreases directly with the increase in cerium content instead of being abnormal when there is no GB phase in magnets at all or the value of magnetocrystalline anisotropy or exchange integral is too large.

Properties of magnetically semi-hard (FexCo1−x)3B compounds

The (FexCo1−x)3B (x = 0.0, 0.1, 0.2, 0.3) compounds have been prepared by induction melting with subsequent annealing. All of the compounds form in the orthorhombic Fe3C-type structure and exhibit ferromagnetic behaviour: the Curie temperature increases from 750 K for x = 0.0 to 923 K for x = 0.3. Magnetic domain images obtained by Kerr microscopy reveal the presence of uniaxial magnetocrystalline anisotropy. The magnetocrystalline anisotropy energy and anisotropy field of magnetically oriented fine particles have been determined. An anisotropy energy of 651 kJm−3 was obtained for Co3B (x = 0.0), the anisotropy energy was found to decrease with increasing Fe content reaching a value of 507 kJm−3 for x = 0.3. These compounds with uniaxial magnetocrystalline anisotropy are potential candidates to be used as semi-hard magnetic phase for the preparation of rare-earth free nanocomposite permanent magnets.

Stacked pulse-electroplated CoNiMnP–AAO nanocomposite permanent magnets for MEMS

The paper presents a CMOS compatible pulse-electroplating technique combined with a low temperature bonding process for the synthesis of CoNiMnP–AAO (anodic alumina oxide) nanocomposite films and the fabrication of stacked composite permanent magnets (PMs). The magnetic nanocomposite film exhibits the best characteristics of the coercivity of 2472 Oe, remanence of 4000 G, and of 16.13 kJ m−3, in the existing CoNiMnP systems. Meanwhile, a surface magnetic flux density of 9.2 mT generated by a 15-layer-stacked composite PM with a volume of 9 mm3 has shown the potential for various magnetic microelectromechanical systems (MEMS) fabrication using the nanocomposite material.

Investigation of magnetic properties of MnBi/Co and MnBi/Fe65Co35 nanocomposite permanent magnets by micro-magnetic simulation

Demagnetization curves of anisotropic nanocomposite MnBi/Co and MnBi/Fe65Co35 permanent magnets were investigated by micro-magnetic finite element method. Effects of volume ratio, deviation degree of orientation and intrinsic magnetic properties of the soft magnetic phase on the magnetic properties of the magnets were investigated. From the viewpoint of practical applications, to meet the requirement of hardness parameters, ĸ=K/(μ0MS2)1/2>1, the calculation maximum (BH)max of MnBi/Co and MnBi/Fe65Co35 magnets are about 199kJ/m3 (V(Co)=22vol%) and 196kJ/m3 (V(FeCo)=14vol%), respectively, indicating their good potential in application. Compared with single phase MnBi magnet, the (BH)max of nanocomposite MnBi/Co and MnBi/Fe65Co35 magnets increases by 66% and 63%, respectively. The remanence and coercivity of MnBi/Co nanocomposite magnets reduce as appearing a deviation degree of orientation, result of greatly decrease of the magnetic energy product.

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

Abstract The magnetic properties, phase evolution and microstructure of Fe70−xMxB19Nd7Nb4 (M=Si, Gd, Si+Gd; x=0–2.5 at%) bulk nanocomposite permanent magnets in the form of rods produced by annealing the amorphous precursor have been investigated systematically. Microstructural examination, three-dimensional atom probe microanalysis, δM-plots, X-ray diffraction analysis and magnetometer studies deduced that good magnetic properties in the magnets originate from the homogenous microstructure consisting of exchange coupled, soft magnetic (α-Fe, Fe3B) and hard magnetic (Nd,Gd)2Fe14B nanophases. Optimally annealed Fe70B19Nd7Nb4 rod magnets exhibit magnetic properties of Br=0.61 T, iHc=876 kA/m and (BH)max=50.2 kJ/m3. Gadolinium and silicon addition to quaternary Fe70B19Nd7Nb4 alloy increased the mass fraction of hard magnetic phase, strengthened the exchange coupling interactions and enhanced the magnetic properties. Gadolinium and silicon segregated into hard magnetic phase which led to enhance coercivity up to 1115 kA/m. Enhancement in the coercivity is mainly resulted by hard phase increment as well as domain wall pinning, while strengthening of exchange coupling is caused by grain size refinement and increase in Curie temperature of the magnetic phases. The Fe67B19Nd7Gd2Nb4Si1 magnetic rods of 1.2 mm in diameter demonstrated the best magnetic properties such as intrinsic coercivity, iHc of 1115 kA/m, remanence, Br of 0.57 T and maximum energy product, (BH)max of 65.7 kJ/m3.

Occupancy of 4d-states in T (T: Mo, Nb) from NEXAFS L 3,2 Spectra of Nd-Fe-B-T Alloys

Introduction. Neodymium-iron-boron nanocomposite permanent magnets were developed in the early 1990s [1, 2]. Their low neodymium content, less than the stoichiometric amount of 12 at.%, made them cheaper and more corrosion resistant. Moreover, their higher boron content improves the amorphization ability. These systems, called exchange-spring magnets, exhibit interesting magnetic properties due to the exchange coupling between the hard and soft magnetic phases at nanoscale. The coexistence of both types of magnetic phases results in rema nence and magnetic energy product ((BH)max) enhancement. However, the presence of the soft phases reduces the coercivity. The use of alloying components such as Mn, Cu, Nb, Ti, and Mo, among others, helps to control the grain growth during the melt-spinning production of these kind of magnets, improving in this way the magnetic response of the material [3–5]. In particular, the addition of Mo and Nb was reported to be very effective for grain refi nement of nanocomposites, leading to the improvement of the coercivity after annealing [6]. However, the mechanisms that cause the suppression of α-Fe formation are not fully understood, as well as the role of Mo or Nb as an additive component that helps to stabilize the Nd2Fe14B phase (ϕ-phase). Urse et al. explained the coercivity enhancement by the pinning of domain walls at grain boundaries where the additive precipitates, in the case of Modoped Nd-Fe-B thin fi lms [7]. For Nb-doped ribbons, it was found that a higher concentration of this additive is required than in the case of Mo in order to obtain higher coercivities and (BH)max [8]. Thus, a study of the electronic state of these elements becomes appropriate to elucidate the role they play as additives in Nd-Fe-B magnets. Synchrotron radiation is a powerful tool that helps in this study. The information on the electronic structure of occupied/unoccupied 4d-electron states in these alloys was derived from near-edge X-ray absorption fine structure (NEXAFS) measurements. The purpose of the present work is to quantify, by X-ray absorption spectroscopy, variations in occupancy of the 4d-states of molybdenum and niobium added to NdFeB alloys produced by the melt spinning technique, both as quenched (AQ) and subsequently annealed (TT), and to identify correlations between these results and magnetic features of the alloys. Experimental. The starting ingots with nominal compositions of NdyFe(86–y–x)B14Tx (T: Mo, Nb; x = 2, 4; y = 7, 8) were prepared by arc melting of pure elements in argon atmosphere. The ribbons were produced by rapid solidifi cation of molten alloy (melt-spinning) with a roll speed of 20 m/s. Ribbons were sealed in quartz ampoules in a protective atmosphere of argon. Then, the overquenched ribbons were annealed at 973 K for 20 min. The thickness of the ribbons was about 20 μm. From here, the samples are identifi ed by their x and y values, namely, TxNdy (T: Mo, Nb). The measurements (fl uorescence mode) were carried out at the SXS beamline (source: D04A bending magnet) of the Laboratorio Nacional de Luz Sincrotron, Campinas, Brazil. X-ray absorption data were analyzed using standards procedures: a linear background was fi tted at the pre-edge region and then subtracted from the entire spectrum; the jump of the spectrum

Microstructure and magnetic properties of directly quenched Nd2Fe14B/α-Fe nanocomposite materials at different temperatures

Directly quenched Nd9.5Fe81Zr3B6.5 nanocomposite permanent magnets were prepared under different melt treatment conditions, i.e., the melt temperature was varied prior to ejection onto the quenching wheel. The effect of quenching temperature on the microstructure and magnetic properties of the alloys was studied by X-ray diffractometry, transmission electron microscopy and magnetization measurements. It is found that a finer and more uniform microstructure can be obtained directly from the melt quenched at lower temperature. With increasing initial quenching temperature, the optimal quenching speed decreases and the microstructure of the ribbons becomes coarser and more irregular. As a result, the magnetic properties of the alloys are deteriorated. It is believed that the break of the pre-existing Nd2Fe14B clusters and decrease in number of the developing nuclei of Nd2Fe14B phase with increase in quenching temperature may be the causes for the change of the microstructure and the magnetic properties of the ribbons.

Micromagnetic finite element simulation of nanocrystalline α-Fe/Nd2Fe14B/Fe3B magnets

Nanocomposite Nd2Fe14B permanent magnets with Fe3B and α-Fe as the soft phase have been simulated using micromagnetic modelling. This paper reviews extensively the results from the simulation point of view. The magnetization configuration along the hysteresis loop is discussed in details. It was clear that the grain size and phase distribution play important roles in determining the magnetic properties. By changing the size of the grain and the volume fraction of the hard and soft phase, the magnetic properties change and the relationship between microstructure and properties is investigated. The remanence, Jr increases with decreasing of grain size, but oppositely for coercivity, Hc. The highest Jr, 1.46T was obtained with a grain size 10nm, and volume fraction of α-Fe, 40%. Whereas, the highest Hc with combination Nd2Fe14B 80% and 20% Fe3B, 947kA/m. On the other hand, if Nd2Fe14B alone, the Hc able to reach up to 1000kA/m. From this study, micromagnetic modelling contributes to a better understanding how microstructure and phase distribution influences the magnetic properties.

Iron oxide nanocomposite magnets produced by partial reduction of strontium hexaferrite

Isotropic bulk nanocomposite permanent magnets were produced with strontium hexaferrite, SrO·6Fe2 O3 , and magnetite, Fe3 O4 , as the magnetically hard and soft components. A novels synthesis scheme based on the partial reduction of SrO·6Fe2 O3 was employed. In two parallel experiments, nano- and microcrystalline SrO·6Fe2 O3 particles were compacted into pellets along with a controlled, understoichiometric amount of potato starch as a reducing agent. The pellets were then sintered in a passive atmosphere. Based on XRD and room temperature magnetic hysteresis measurements, it was concluded that a fraction of the SrO·6Fe2 O3 input material had been reduced into Fe3 O4 . In comparison with pure SrO·6Fe2 O3 control pellets, these composites exhibited maximum energy product increases in excess of 5 % due to remanence boosting. The improvement of magnetic properties was attributed to an efficient exchange spring coupling between the magnetic phases. Interestingly, as the synthesis scheme also worked for microcrystalline SrO·6Fe2 O3 , the method could presumably be adapted to yield crystallographically oriented bulk nanocomposite magnets.

Effect of α-Fe Content on the Magnetic Properties of MnBi/α-Fe Nanocomposite Permanent Magnets by Micro-magnetic Calculation

A finite element model was built for MnBi/α-Fe nanocomposite permanent magnets, and the demagnetization curves of the magnets were simulated by micro-magnetic calculation. The microstructure of the cubic model is composed of 64 irregular grains with an average grain size of 20 nm. With the volume fraction of soft magnetic phase (t vol. %) ranged from 5 to 20 vol. %, both isotropic and anisotropic nanocomposite magnets show typical single-phase permanent magnets behavior in their demagnetization curves, illustrating good intergranular exchange coupling effect between soft and hard magnetic phases. With the increase of volume fraction of soft magnetic phase in both isotropic and anisotropic magnets, the coercive force of the magnets decreases monotonically, while the remanence rises at first to a peak value, then decreases. The optimal values of maximum energy products of isotropic and anisotropic magnets are 84 and 200 kJ/m 3 , respectively. Our simulation shows that the MnBi/α-Fe nanocomposite permanent magnets own excellent magnetic properties and therefore good potential for practical applications.

Investigation of Magnetic Properties of MnBi/$\alpha$-Fe Nanocomposite Permanent Magnets by Micro-Magnetic Simulation

In the present study, the demagnetization curves of MnBi/α-Fe nanocomposite permanent magnets were calculated by the micromagnetic finite element method. The effect of volume ratio between magnetically soft α-Fe phase and MnBi hard phase on the magnetic properties of magnets was investigated. The sample used in the present simulation was consisted of 91 spherical fourteen faces units of hard phase grains with diameter of 20 nm, and the soft matrix phase with the thickness (t) ranging from 1 to 6 nm. For the isotropic MnBi/α-Fe magnets, as increases, the remanence (B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> )increases first, peaks at 0.855 T for t = 3 nm, then decreases again, while the coercivity (H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ci</sub> ) drops monotonically from 691 kA/m for t = 1 nm to 94 kA/m for t = 6 nm. The sample with t = 2 nm has the optimal maximum energy product (BH) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> = 55.15 kJ/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . For the anisotropic magnets, the B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> and H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ci</sub> exhibit their t-dependent behavior similar to that of the isotropic ones. The optimal values of B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> , H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ci</sub> and (BH) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> are 1.47 T, 3200 kA/m, and 322 kJ/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> when t = 5,1, and 3 nm, respectively, indicating a good potential of the anisotropic MnBi/α-Fe nanocomposite as practical permanent magnets.

Anisotropic Sm2Co17 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.

ChemInform Abstract: One‐Step Hydrothermal Synthesis and Characterization of High Magnetization CoFe2O4/Co0.7Fe0.3 Nanocomposite Permanent Magnets.

AbstractThe title nanocomposite permanent magnets are hydrothermally synthesized from a mixture of CoCl2, (NH4)2Fe(SO4)2, sodium citrate, NaOH, and H2O (autoclave, 80—180 °C, 24 h).

One-step hydrothermal synthesis and characterization of high magnetization CoFe2O4/Co0.7Fe0.3 nanocomposite permanent magnets

CoFe2O4/Co0.7Fe0.3 nanocomposite permanent magnets have been synthesized in one step by a hydrothermal method at reaction temperatures of 80, 120, 140, 160 and 180°C and characterized by XRD, SQUID, SEM, (HR)TEM, and SAED. All samples consisted of octahedral CoFe2O4 particles and spherical-like Co0.7Fe0.3 particles. The maximum magnetization and coercivity were 191emu/g and 1311Oe, respectively, values not previously observed for the CoFe2O4/Co0.7Fe0.3 system. This maximum magnetization was attributable to the larger mass ratio of Co0.7Fe0.3 to CoFe2O4, which were in intimate contact. Magnetic dipolar interaction plays a crucial role in magnetic properties and leads to the reduction of the magnetization and the Mr/Ms ratio. The coercivity of all samples exhibited complex variation with reaction temperature and its mechanism may deserve further investigation.

Crystallization Behavior and Curie Temperature Properties of Al Doped Nd-Fe-B Based Nanocomposite Permanent Magnet

The work is primarily concerned with the development of nanocrystalline Nd-Fe-B, based permanent magnet with high Curie temperature. An alloy of composition Fe81Nd7Al2B10 has been prepared using vacuum arc furnace and subjected to using Melt-Spinning process for preparation of amorphous flakes. Differential scanning calorimetry (DSC) has been performed to determine the crystallization temperature and activation energy of the melt spun amorphous ribbons. Subsequently the melt spun ribbon was subjected to annealing at below and above the crystallization temperatures to identify effect of Al on the Curie temperature. It was noteworthy for the effect of alloying Al above crystallization temperature. The Curie temperature increases to by almost 1.3 times with increase in annealing temperature.

Investigation on magnetic properties of orientated nanocomposite Pr2Fe14B/α-Fe permanent magnets by micromagnetic finite-element method

Demagnetization curves for nanocomposite Pr2Fe14B/α-Fe permanent magnets with different hard grain alignment are calculated by a micromagnetic finite-element method. The results show that both remanence and coercivity increase with improving hard grains alignment. The demagnetization curves show a single-phase demagnetization behavior for the samples with grain size d of 10nm and two-phase behavior for the samples with d of 20 and 30nm. Hex (reflecting the magnetic hardening of α-Fe) and Hirr (expressing the irreversible reversal of hard phase) are both enhanced with improving the hard grain alignment. The magnetic reversal in orientated nanocomposite permanent magnets is mainly controlled by inhomogeneous pinning of the nucleated type.

Structure and magnetic properties of bulk anisotropic SmCo5/α-Fe nanocomposite permanent magnets prepared via a bottom up approach

Surfactant assist ball milling, chemical coating, and hot compaction techniques have been applied to prepare bulk anisotropic SmCo5/α-Fe nanocomposite permanent magnets. The effects of α-Fe content on the structure and magnetic properties of the magnets were studied. As the α-Fe content increases, the remanence of the magnets increases first, peaking at 5wt.% of α-Fe content, then falls as the α-Fe content increases, while the coercive force of the magnets drops simultaneously. Crystal structure analysis shows that all the magnets exhibit noticeable c-axis crystal texture of SmCo5 phase. The SmCo5/α-Fe magnet with 5wt.% α-Fe possesses M2.3T of 78.68emu/g, Mr of 70.03emu/g, and Hci of 8.02kOe.

Nd5Fe64B23Mo4Y4 bulk nanocomposite permanent magnets produced by crystallizing amorphous precursors

The glass forming ability and magnetic properties of Nd5Fe68−xB23Mo4Yx (x=0, 2, 4, 6) alloys prepared by copper mold casting technique have been studied. Amorphous rods with a diameter of 2mm were obtained in the Nd5Fe64B23Mo4Y4 alloy. After annealing for 10min at 1013K, the Nd5Fe64B23Mo4Y4 alloy showed optimal hard magnetic properties with the coercivity of 764.2kA/m, remanence of 0.6T and maximum energy product of 57.3kJ/m3, respectively. The enhanced magnetic properties can be ascribed to the strong exchange coupling among the magnetically soft α-Fe (25–30nm), Fe3B (30–35nm) and hard Nd2Fe14B (40–50nm) grains present in the magnet microstructure. Large size bulk nanocomposite magnets with sound magnetic properties make the Nd–Fe–B–Mo–Y alloy system a promising candidate for industrial applications.

Fe64B22.8Nd6.6Y3.9Nb2.7 bulk nanocomposite magnets with improved size and magnetic properties

Abstract