Nanocomposite Permanent Magnets Research Articles

Unusual effects of Ti and C additions on structural and magnetic properties of Nd–Fe–B nanocomposite magnets in a B-rich and Nd-poor composition range

Effects of Ti and C additions on structural and magnetic properties of Fe x B/Nd 2Fe 14B-type nanocomposite permanent magnets ( x=3 or 23 6 ) prepared by means of rapid solidification and subsequent annealing in a B-rich and Nd-poor composition range are reported. Addition of Ti suppresses formation of primary Fe and promotes formation of ferromagnetic iron-borides. Carbon addition is effective for grain refinement and suppression of unfavorable formation of TiB 2, resulting in improvement of magnetic properties. Compositional adjustments have yielded a series of Fe x B/Nd 2Fe 14B-type isotropic nanocomposite permanent magnets with magnetic performance comparable to near-single-phase isotropic melt-spun magnets in a composition range B>10 at% and Nd<10 at% .

Magnetization and demagnetization behaviours of melt-spun Pr 12 Fe 82 B 6 and Pr 8 Fe 87 B 5 ribbons

Nanocrystalline Pr12Fe82B6 and nanocomposite Pr8Fe87B5 ribbons have been prepared using a melt spinning technique. Recoil loops have been measured at 20, 200 and 300K. Demagnetization curves are analysed by dividing it into reversible and irreversible portions. High recoil loop susceptibility at low applied field and large reversible change in the demagnetization curve have been found in Pr8Fe87B5 ribbons, showing that the reversible behaviours in nanocomposite permanent magnets originate primarily from the magnetically soft phase. The hysteresis in recoil loops found in Pr8Fe87B5 ribbons originates from the soft phase ?-Fe that suffers a stress.

Development of Industrial Nanocomposite Permanent Magnets: A Review

Development of industrial nanocomposite permanent magnets (NCPM) is reviewed with a particular emphasis on rare-earth-iron-based materials. After a brief description of the basic concepts concerning NCPM, leading discoveries of iron-based NCPM are reviewed. The impact of recent development of high-coercivity Nd-Fe-B-Ti-C isotropic NCPM powders that are industrially produced by applying strip casting process for rapid solidification is described. Short comments on bulk NCPM and empirical efforts toward anisotropic NCPM are also included. Application aspects of the industrial NCPM are discussed.

Ｆｅ３Ｂ／Ｎｄ２Ｆｅ１４Ｂ系ナノコンポジット磁石におけるナノ組織形成とＴｉ‐Ｃ添加効果

The continuous cooling curves during melt-spinning process of typical Fe3B/Nd2Fe14B-type nancomposite permanent magnet alloys Nd4Fe77.5-xTxB18.5 where T is Cr or Cu were measured using the infrared imaging technique and a continuous cooling transformation (CCT) diagram was constructed. The CCT diagram suggested that the effect of T was kinetic and phase selective. Effects of Ti and C additions on phase selection during rapid solidification were investigated in a Nd-poor and B-rich concentration region where the unfavorable Nd2Fe23B3 metastable phase becomes prevailing. The Ti-C addition was found to promote crystallization of Nd2Fe14B and prevents formation of γ-Fe. Utilizing this knowledge, a series of high coercivity Fe-B/Nd2Fe14B-type nanocomposite permanent magnets were developed on the basis of Nd-Fe-B-Ti-C system.

Investigation of intergrain exchange coupling interaction of nanocrystalline permanent magnets by numerical simulation

The initial curves, demagnetization curves and recoil curves of Pr2Fe14B and Pr2Fe14B-α Fe nanocrystalline permanent magnets have been calculated by micromagnetic finite_element method. The validity of δm(H)curves, which can be used to determine the strength of intergrain exchange coupling interaction (IGEC), is approved by the calculated results. It is found that IGEC weakens with increasing grain size D for single-phase nanocrystalline and nanocomposite permanent magnets. Thus, the demagnetization curve shows a two-phase behavior and the δm(H) curve shows two peaks for the nanocomposite sample with D=20nm.The peak at small field can be attributed to the exchange interaction between the magnetic hard and soft grains, while the peak at large field may be due to the IGEC among hard grains.

Investigation of high-performance hard magnetic properties of nanocomposite permanent magnets by micromagnetic finite element method*

The microstructure with which a hard magnetic phase precipitates from the soft magne ticmatrix, is observed in nanocomposite Pr2Fe14B-αFe. The magnetic hysteresis loo ps are simulated by micromagnetic finite element method. The dependence of reman ence, coercivity and maximum energy product on the width of soft phase are discu ssed in detail. Although a single hard magnetic phase behavior is observed, the coercivity decreases monotonically with the increase of soft phase width from 0 to 12 nm. The obtained maximum energy products are 184 and 674 kJ/m3 for isotropic and anisotropic magnets, respectively.

Study on the Magnetic Properties and Microstructure of Nd-Fe-B Nanocomposite Permanent Magnets

Study on the Magnetic Properties and Microstructure of Nd-Fe-B Nanocomposite Permanent Magnets

Role of amorphous grain boundaries in nanocomposite NdFeB permanent magnets

Two typical Nd–Fe–B permanent magnetic alloys of B-enriched Nd4.5Fe77B18.5 and Fe-enriched Nd9Fe85B6Zr0.5 have been employed to study the effect of annealing on the microstructure and the magnetic properties, respectively. It has been found that the maximum remanence, remanence ratio, intrinsic coercivity, and energy product are 1.32 T, 0.86, 212 kA/m, and 130 kJ/m3, respectively, for the B-enriched alloy, while they are 1.15 T, 0.82, 496 kA/m, and 162 kJ/m3, respectively, for the Fe-enriched alloy. In these samples, x-ray diffraction, Mössbauer spectroscopy, and high-resolution transmission electron microscopy revealed the existence of an amorphous phase between grains. It is believed that enhancement of the remanence and remanence ratio in the magnets originates from the amorphous grain boundaries, which increase the exchange coupling between neighboring grains.

Bulk nanocomposite permanent magnets produced by crystallization of Fe66.5Co10Pr3.5B20 bulk glassy alloy

The glass-forming ability, thermal stability, crystallized structure, and magnetic properties have been investigated for an Fe66.5Co10Pr3.5B20 glassy alloy with a large supercooled liquid region of 43 K before crystallization and a high reduced glass transition temperature of 0.56. The glassy phase is formed in a rod form with a diameter of 0.5 mm by copper mold casting. The crystallized nanocomposite structure consists of Fe3B, α-Fe and Pr2Fe14B phases, and the remanence (Br), coercivity (iHc), and maximum energy product (BH)max are 1.23 T, 225 kA/m, and 95.9 kJ/m3, respectively, for the cast rod annealed at 863 K for 600 s. The present study shows the possibility of producing bulk Pr2Fe14B/(Fe3B,α-Fe) nanocomposite permanent magnets by the simple process of copper mold casting and heat treatment.

Bulk nanocomposite permanent magnets produced by crystallization of (Fe,Co)–(Nd,Dy)–B bulk glassy alloy

The glass-forming ability, thermal stability, and magnetic properties have been investigated for an Fe67Co9.4Nd3.1Dy0.5B20 glassy alloy with a large supercooled liquid of 48 K before crystallization prepared by copper mold casting. The glassy phase is formed in a rod form with a diameter of 0.5 mm. The crystallized nanocomposite structure consists of Fe3B, α-Fe, and Nd2Fe14B phases, and the remanence (Br), coercivity (iHc) and maximum energy product (BH)max are 1.19 T, 244 kA/m, and 92.7 kJ/m3, respectively, for the rod of 0.5 mm in diameter annealed at 913 K for 600 s.

Effect of amorphous grain boundaries on the magnetic properties of B-rich nanocomposite permanent magnets

A typical B-rich Nd–Fe–B permanent magnetic alloy with composition Nd 4.5Fe 77B 18.5 has been chosen to study the effect of an amorphous grain boundary on the exchange coupling interaction. Amorphous ribbons have been prepared by melt spinning. After optimized annealing, there is a residual amorphous grain boundary phase in the specimen. This sample exhibits better magnetic properties than the completely crystallized specimen. The remanence, remanence ratio, intrinsic coercivity and energy product of the optimum sample with a residual amorphous phase are 1.32 T, 0.86, 212 kA/m, and 130.3 kJ/m 3, respectively. X-ray diffraction, Mössbauer spectra and high-resolution TEM observation suggest that the enhancement of the remanence ratio in the magnet with a residual amorphous intergranular layer results from the amorphous grain boundary which is favorable for enhancing the exchange coupling interaction between neighboring grains. The role of the amorphous grain boundary in the exchange coupled magnet has been discussed.

Magnetic properties and microstructure of SmCo 5+α-Fe nanocomposite magnets prepared by mechanical alloying

Preparation of nanocomposite permanent magnets composed of SmCo 5 as a hard magnetic phase and α-Fe as a soft magnetic phase has been tried by mechanical alloying of a mixture of SmCo 5 and α-Fe powders and subsequent heat treatment for crystallization. The amount of the soft α-Fe phase was varied, and the effects of Fe content on the magnetic properties have been investigated. The mechanically alloyed (SmCo 5) 1− x Fe x powders were found to be composed of the Sm–Co amorphous phase and the α-Fe phase. The composite of a SmCo 5 phase (1-5 phase) and an α-Fe phase obtained by heat treatment at 823 or 873 K. On the other hand, after crystallization at 923 or 1073 K, the 2-17 phase was formed instead of the 1-5 phase. The (SmCo 5) 1− x Fe x powders crystallized at 873 K showed fine microstructures composed of grains 10–20 nm in size. The values of remanence Mr of the (SmCo 5) 1− x Fe x powders significantly increased with increasing Fe content, on the other hand, the values of coercivity linearly decreased. The maximum value of maximum energy product (BH)max, 105.8 kJ/m 3, was obtained for the (SmCo 5) 75Fe 25 powder. In the demagnetization curves of the (SmCo 5) 1− x Fe x powders in the second quadrant, any step due to the presence of soft phases was not detected and the recoil loops showed a large reversible magnetization reaching about 60%. From these results, it is evident that exchange coupling between the soft and hard phases was obtained in this study.

Influence of heating rate on the microstructure and magnetic properties of Fe 3B/Nd 2Fe 14B nanocomposite magnets

The influence of heating rate on the microstructure and magnetic properties of the Fe 3B/Nd 2Fe 14B nanocomposite permanent magnet materials produced by the crystallization of the Nd 4.5Fe 73B 18.5Co 2Cr 2 amorphous alloy has been studied.

Effects of Cu-Nb/Zr addition on magnetic properties of Fe/sub 3/B/(Nd-Dy)/sub 2/Fe/sub 14/B nanocomposite magnets

Improving magnetocrystalline anisotropy to create materials with high coercivity by means of partial replacement of Nd with a heavy rare earth element such as Tb and Dy requires considerable refinement of grain size in order to keep the relation between intergranular exchange energy and magnetocrystalline energy unchanged. Addition of small amounts of Cu and Zr is shown to be effective to manipulate crystallization behaviors and hence structure of the Fe/sub 3/B/Nd/sub 2/Fe/sub 14/B-type nanocomposite permanent magnets containing heavy rare earth elements. The impact of the simultaneous addition of Cu-Zr is that improvement of magnetic properties can he achieved with a smaller amount of additives than Cu-Nb addition reported earlier. An example is Nd/sub 3.4/Dy/sub 1.0/Fe/sub 71.7/B/sub 18.5/Cr/sub 2.4/Co/sub 2.4/Cu/sub 0./ /sub 4/Zr/sub 0.2/ with H/sub cJ/=462 kA/m, B/sub r/=0.97 T, and (BH)/sub max/=105 kJ/m/sup 3/.

Effect of annealing on magnetic exchange coupling in CoPt/Co bilayer thin films

Thin film CoPt/Co bilayers have been prepared as a model system to investigate the relationship between microstructure and exchange coupling in two-phase nanocomposite permanent magnets. The bilayers were prepared by magnetron sputter deposition of near-equiatomic CoPt with a thickness of 25 nm onto oxidized Si wafers. In the as-deposited state, CoPt had the A1 (fcc) structure and was magnetically soft. Before reinsertion into the sputtering chamber for the deposition of 2.8–16.7 nm thick Co layers, the CoPt films were annealed at 700 °C for 120 min to produce the magnetically hard, fully ordered L10 phase. The presence of exchange coupling in the bilayers was verified by magnetic hysteresis and recoil measurements and showed that only for Co thicknesses below 6.3 nm was this layer (in its as-deposited state) coupled through its full thickness to the CoPt layer. Annealing the bilayer samples at 300 and 550 °C for 20 min resulted in improvement of the interlayer magnetic coupling and produced clear differences in the magnetic reversal coherency and the recoil curves. However, for some samples, the improved coupling resulted in a decrease in coercivity, indicating that there is an optimum in the coupling strength for the attainment of high coercivity. Transmission electron microscopy studies of the bilayers in plan view showed that the increased interlayer coupling with annealing was a result of improved granular epitaxy of Co to CoPt.

Ｃｒ‐Ｃｏ添加Ｆｅ３Ｂ／Ｎｄ２Ｆｅ１４Ｂ系交換スプリング磁石の磁気特性と安定性

The effect of co-addition of Cr and Co to Fe3B/Nd2Fe14B exchange-spring nanocomposite permanent magnets on the magnetic properties and their stability was investigated. It was found that HcJ of Fe3B/Nd2Fe14B exchange-spring magnets can be controlled in the range from 300 kA/m to 600 kA/m by adjusting the Cr and Nd concentrations. The squareness of the demagnetizion curves is improved by simultaneous addition of Cr and Co. Thermal stability is also improved by Cr addition: irreversible flux losses rate of the 5 at% Cr-doped Fe3B/Nd2Fe14B exchange-spring magnets were about 1 % after exposure to a temperature of 100°C. This type of magnets are less susceptible to oxidation because the rare-earth content is lower than that of conventional Nd2Fe14B isotropic powders. The higher packing density can be obtained because of the round shape of the pulverized Fe3B/Nd2Fe14B exchange-spring magnet. Consequently, Fe3B/Nd2Fe14B exchange-spring magnet powders are suitable for the injection-molding process in which the magnetic powders are exposed to high temperatures.

Microstructural evolution of Fe 3B/Nd 2Fe 14B nanocomposite magnets microalloyed with Cu and Nb

The microalloying effect of Cu and Nb on the microstructure and magnetic properties of an Fe 3B/Nd 2Fe 14B nanocomposite permanent magnet has been studied by transmission electron microscopy (TEM) and atom probe field ion microscopy (APFIM). Additions of Cu are effective in refining the nanocomposite microstructure and the temperature range of the heat treatment to optimize the hard magnetic properties is significantly extended compared with that of the ternary alloy. Combined addition of Cu and Nb is further effective in reducing the grain size. Optimum magnetic properties obtained by annealing a melt-spun Nd 4.5Fe 75.8B 18.5Cu 0.2Nb 1 amorphous ribbon at 660°C for 6 min are B r=1.25 T, H cJ=273 kA/m and ( BH) max=125 kJ/m 3. The soft magnetic Fe 23B 6 phase coexists with the Fe 3B and Nd 2Fe 14B phases in the optimum microstructure of the Cu and Nb containing quinternary alloy. Three-dimensional atom probe (3DAP) results show that the finer microstructure is due to the formation of a high number density of Cu clusters prior to the crystallization reaction, which promote the nucleation of the Fe 3B phase. The Nb atoms appear to induce the formation of the Fe 23B 6 phase when the remaining amorphous phase is crystallized.

Mechanism of grain size refinement of Fe3B/Nd2Fe14B nanocomposite permanent magnet by Cu addition

Minor addition of Cu to Nd4.5Fe77B18.5 melt-spun alloy is effective on reducing the grain size of the Fe3B/Nd2Fe14B nanocomposite permanent magnet produced via the crystallization route from the amorphous phase, thereby improving hard magnetic properties. Three-dimensional atom probe and transmission electron microscopy observations have shown that Cu clusters with a number density of ∼1024 m−3 is formed prior to the nucleation event of the Fe3B primary crystal. In the nucleation and growth stage of the Fe3B primary crystals, Cu clusters are in direct contact with the primary particles, suggesting that Cu clusters serve as heterogeneous nucleation sites for the Fe3B primary particles, thereby increasing the number density of the particles.

Materials Properties and Utilization of Fe3B/Nd2Fe14B-Type Nanocomposite Permanent Magnets Based on Nd-Fe-Cr-Co-B

ABSTRACTRecent progresses of materials development and their utilization of Cr-and-Co-doped Fe3B/Nd2Fe14B-type nanocomposite permanent magnets are reported. A practical balance between enhanced intrinsic coercivity and temperature stability of magnetic properties has been realized by simultaneous additions of Cr and Co. This type of magnets are less susceptible to oxidation because of the less rare-earth content. Consequently, even fine powders (e. g., under 38 micrometer sieve) are physically and chemically stable in contrast to the conventional Nd2Fe14B-type melt-spun materials. The stability in terms of the structural losses is also superior to that of the Nd2Fe14B-type melt-spun materials. Utilization of the Cr-and-Co-doped Fe3B/Nd2Fe14B nanocomposite permanent magnets as a hard magnetic component of injection-molded resin-bonded magnets seems promising because of the excellent stability of the magnetic properties of fine powders. Direct quenching of a melt into the nanocomposite structure has become possible recently in addition to the conventional processing route of crystallization of an amorphous precursor, opening up the possibility of less-expensive production of the material.

Effect of Cu Addition on the Microstructure and Magnetic Properties of an Fe3B/Nd2Fe14B Nanocomposite Magnet.

The microalloying effect of Cu addition on the microstructure and magnetic properties of Fe3B/Nd2Fe14B nanocomposite permanent magnets has been investigated. With the optimum heat-treatment condition, Cu-containing alloy exhibits a much finer nanocomposite microstructure. Three-dimensional atom probe (3DAP) results have revealed that Cu and Nd form a high density (∼1024m-3) of Cu-Nd clusters containing 5.0 at.% Cu and 7.0 at.% Nd prior to the crystallization reaction of the Nd4.5Fe76.8B18.5Cu0.2 amorphous alloy. These clusters serve as heterogeneous nucleation sites for the Fe3B primary crystals. In the final Fe3B/Nd2Fe14B nanocomposite microstructure, Cu dissolves uniformly in the Nd2Fe14B hard magnetic phase. Improved magnetic properties have been obtained in the Cu-containing alloy; these are attributed to the reduction in the grain size due to the addition of Cu.