Nanocomposite Ribbons Research Articles

Magnetic and crystalline microstructures of Fe–B/FePt-type Nanocomposite ribbons with high permanent properties

We present a magnetic force microscopy and atomic force microscopy study of magnetic and crystalline microstructures of melt-spun binary Fe 50+ x Pt 50− x ( x=0−20) and ternary (Fe 0.5+ y Pt 0.5− y ) 82B 18( y=0−0.2) nanocomposite ribbons. It was confirmed that an ordered magnetically hard γ 1-FePt phase could be fully formed at x⩽10 in Fe 50+ x Pt 50− x ribbons. From the topographic images of the Fe 50+ x Pt 50− x and (Fe 0.5+ y Pt 0.5− y ) 82B 18 ribbons, it was found that the average crystal size D ¯ is large (∼1.1–3.9 μm) for the Fe 50+ x Pt 50− y ribbons without B, but that of the (Fe 0.5+ y Pt 0.5− y ) 82B 18 ribbons with invariable B content is much small ( ∼57–65 nm). Moreover, the magnetic force images with distinct contrast could be detected by MFM only in the ribbons with strong exchange-coupling interaction. Finally, it was found that for exchange-coupling nanocomposite ribbons, the strength of the exchange-coupling interaction can be reflected roughly by the root-mean-square roughness of phase shift, ( Δ φ ) rms , of magnetic force images and the ratio of the average domain width w ¯ to the average crystal size D ¯ .

Magnetic Properties and Microstructure of (Fe 0.5+yPt 0.5-y) zB 100-z(y=0–0.2; z= 82 and 84) Melt Spun Ribbons

The Fe-B/FePt-type nanocomposite ribbons with strong exchange-coupling and high permanent magnetic properties have been developed by the melt-spinning method. For ternary (Fe 0.5+yPt 0.5-y) zB 100-z (y=0–0.2; z=82 and 84), multiple phases, namely γ 1, Fe 2B and Fe 3B, with nanoscaled grain sizes (25–35 nm) can readily form in ribbons after an isothermal annealing at 500 °C. Strong exchange-coupling between grains was found in these ribbons, giving rise to an enhancement of not only the remanence but also the maximum energy product. An iH c of more than 12 kOe has been obtained in (Fe 0.6Pt 0.4) 82B 18 (B r= 6.6 kG, (BH) max=8.9 MGOe), and a B r of 9.4 kG, ft of 7.5 kOe and (BH) max of 14.0 MGOe can be achieved in (Fe 0.675Pt 0.325) 84B 16. Magnetically soft Fe 2B and Fe 3B were found to present in the matrix, as evidenced by high resolution transmission electron microscopy. Because of the higher saturation magnetization of Fe 3B than Fe 2B, the coexistence of Fe 3B with Fe 2B and γ 1 phases was believed the main cause to result in the improved remanence and magnetic energy product of the (Fe 0.675Pt 0.325) 84B 16 ribbons.

Rapid magnetic hardening by rapid thermal annealing in NdFeB-based nanocomposites

A systematic study of heat treatments and magnetic hardening of NdFeB-based melt-spun nanocomposite ribbons have been carried out. Comparison was made between samples treated by rapid thermal annealing and by conventional furnace annealing. Heating rates up to 200 K s−1 were adopted in the rapid thermal processing. It was observed that magnetic hardening can be realized in an annealing time as short as 1 s. Coercivity of 10.2 kOe in the nanocomposites has been obtained by rapid thermal annealing for 1 s, and prolonged annealing did not give any increase in coercivity. Detailed results on the effects of annealing time, temperature and heating rate have been obtained. The dependence of magnetic properties on the annealing parameters has been investigated. Structural characterization revealed that there is a close correlation between magnetic hardening and nanostructured morphology. The coercivity mechanism was also studied by analysing the magnetization minor loops.

Magnetic and Crystalline Microstructures of Fe–Pt–BNanocomposite Ribbons

We investigate magnetic and crystalline microstructures of melt-spun(Fe0.675Pt0.325)100−xBx (x = 12, 14,16, 18, 20) nanocomposite ribbons after optimal thermal treatment usinga magnetic force microscope. The magnetic microstructures arecharacterized by darker spots adjacent to brighter ones in a sub-microscale and in random distribution. It is found that the strength of theexchange coupling interaction between the crystals in the 10–100 nmscale, implied by the maximum value (δM)max of theHenkel plot, could be roughly described by the ratio of theaverage width of the magnetic spots w̄ to the average crystalsize D̄ for the ribbons. Moreover, we find that the intrinsiccoercivity jHc of the ribbons is sensitive to theircrystal sizes, and the smaller D̄, the higher jHc.Finally, by using roughness analysis, the curve of the rootmean square values (δϕ)rms of the phase shift of the magneticforce images versus the boron content x is obtained, which isqualitatively consistent with that of the magnetization σ12 kOe ofthe ribbons versus x.

Effect of Pr concentration on the magnetic properties and phase evolution of Ti-substituted Pr yFe 88− yTi 2B 10 ( y = 9.5–7) nanocomposite ribbons

Magnetic properties, phase evolution, and microstructure of melt spun Pr y Fe 88− y Ti 2B 10 nanocomposite ribbons with different Pr concentration ( y = 9.5–7) have been investigated. For Pr 9.5Fe 78.5Ti 2B 10, only the 2:14:1 phase and the α-Fe phase existed, while an additional Fe 3B phase appears for the ribbons with y = 9–7.5. On further decrease of the Pr content ( y = 7), one extra phase, 2:23:3, is found. The exchange coupling effect, as evidenced by a Henkel plot is found, to decrease with the decrease of the rare earth content, which is attributed to the increasing of grain size with decreasing of Pr content. The magnetic properties of the ribbons first improve with the decrease of y, reaching a maximum at y = 8.5 ( B r = 9.6 kG, i H c = 8.5 kOe, and (BH) max = 17.8 MGOe), then decrease with further decrease of the Pr content ( B r = 9.8 kG, i H c = 5.6 kOe, and (BH) max = 14.5 MGOe for y = 7). In comparison with the Ti-free Pr x Fe 90− x B 10 ( x = 9.5–7) ribbons, improved magnetic properties with higher intrinsic coercivity can be obtained in Pr y Fe 88− y Ti 2B 10 nanocomposites. The maximum magnetic properties of Pr y Fe 88− y Ti 2B 10 nanocomposites can be found in the ribbons with lower rare earth content, i.e. x = 9.5 for the former and y = 8.5 for the latter.

Effect of boron on the magnetic properties and exchange-coupling effect of FePtB-type nanocomposite ribbons

Phase evolution and magnetic properties of melt-spun (Fe0.675Pt0.325)100−xBx (x=12–20) nanocomposite ribbons are investigated. For those ribbons spun at 45m∕s, followed with a 500°C isothermal annealing for 1–6h, the boron addition not only promotes disorder to order (γ→γ1) transformation but also leads to the formation of different kinds of Fe-borides. Pt exhibits a strong affinity to Fe during thermal processes in forming magnetically hard γ1(FePt) phase, leaving excess Fe to interact with B in forming Fe2B, Fe3B, or FeB. For x=12–18, all ribbons are composed of one hard phase, γ1-FePt, and three soft phases, γ-FePt, Fe2B, and Fe3B. But FeB also coexists for x=20. Through the exchange-coupling interaction between nanoscale γ1-FePt and multiple soft phases, record of magnetic properties of Br=9.4kG, Hci=7.5kOe, and (BH)max=14.0MGOe has been successfully developed in isotropic (Fe0.675Pt0.325)84B16 ribbons, where the reduced remanence ratio (σr∕σ12kOe) is as high as 0.86.

Explosive shock processing of Pr2Fe14B/α–Fe exchange-coupled nanocomposite bulk magnets

Explosive shock compaction was used to consolidate powders obtained from melt-spun Pr2Fe14B/α–Fe nanocomposite ribbons, to produce fully dense cylindrical compacts of 17–41-mm diameter and 120-mm length. Characterization of the compacts revealed refinement of the nanocomposite structure, with approximately 15 nm uniformly sized grains. The compact produced at a shock pressure of approximately 1 GPa maintained a high coercivity, and its remanent magnetization and maximum energy product were measured to be 0.98 T and 142 kJ/m3, respectively. The compact produced at 4–7 GPa showed a decrease in magnetic properties while that made at 12 GPa showed a magnetic softening behavior. However, in both of these cases, a smooth hysteresis loop implying exchange coupling and a coercivity of 533 kA/m were fully recovered after heat treatment. The results illustrate that the explosive compaction followed by post-shock heat treatment can be used to fabricate exchange-coupled nanocomposite bulk magnets with optimized magnetic properties.

Study of structural and magnetic properties of B-rich RE–Fe–B nanocomposite ribbons

In this work, a systematic study of the structural and magnetic properties of B-rich rare earth–Fe–B nanocomposite samples produced by annealing amorphous ribbons was carried out. The crystalline Fe 2B phases t-(Fe, RE) 3B and α-(Fe, RE) precipitated at temperatures above 550 °C. The coercive field was found to diminish dramatically, from 1.33 to 0.05 kOe, with the addition of small quantities of Misch-Metal.

Fe–B/FePt-type nanocomposite ribbons with high permanent magnetic properties

The Fe–B/FePt-type nanocomposite ribbons with strong exchange-coupling and high permanent magnetic properties have been developed by the melt-spinning method. For binary Fe 50+ x Pt 50− x ( x=0–20) ribbons spun at 45 m/s, followed by a 500 °C isothermal annealing, an ordered magnetically hard γ 1 (FePt) phase can be fully formed at x⩽10, but the coercivity is merely of less than 2.0 kOe. Nevertheless, for ternary (Fe 0.5+ y Pt 0.5− y ) z B 100− z ( y=0–0.2; z=82 and 84), multiple phases, namely γ 1 , Fe 2B and Fe 3B, with nanoscaled grain sizes (25–35 nm) can readily form in ribbons after an isothermal annealing at 500 oC. Strong exchange-coupling between grains was found in these ribbons, giving rise to an enhancement of not only the remanence but also the maximum energy product. A i H c of more than 12 kOe has been obtained in (Fe 0.6Pt 0.4) 82B 18 ( B r=6.6 kG, ( BH) max=8.9 MGOe), while a new record with a B r of 9.4 kG, i H c of 7.5 kOe and ( BH) max of 14.0 MGOe can be achieved in (Fe 0.675Pt 0.325) 84B 16.

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.

Investigation of magnetic properties, after effect and MFM of Pr yFe 90− yB 10 ( y=8−11.76) nanocomposites

Magnetic properties, coercivity mechanism, after effect of melt-spun Pr y Fe 90− y B 10 ( y=8–11.76) nanocomposite ribbons have been investigated. Exchange coupling effect was evidenced by Henkel plot and confirmed by magnetic force images, to exist in all the ribbons if suitable crystallization treatment was employed. The optimal properties of B r=9.6 kG, i H c=8.3 kOe and ( BH) max=16.2 MGOe were achieved in Pr 9.5Fe 80.5B 10 ribbon. In addition, magnetic force microscopy studies revealed that Pr 9.5Fe 80.5B 10 sample possessing the highest B r showed the biggest (RMS) Δ φ value (1.64°), confirming its strongest exchange coupling effect between grains. Furthermore, the increase of the volume fraction of magnetically soft phases with decreasing Pr concentration leads to the increment of activation volume with decreasing Pr concentration. Moreover, Pr 8Fe 82B 10 having the lowest i H c exhibited maximum values in activation volume V=1.34×10 −18 cm 3, because it possessed the largest volume fraction of the magnetic soft phases, including Pr 2Fe 23B 3, Fe 3B and α-Fe phases.

Processing induced changes in Curie temperature of Nd2Fe14B melt-spun ribbons

Changes of the Curie temperature Tc in Nd2Fe14B (2-14-1) can arise from changes in crystal chemistry or can be induced by compressive stresses. We have recently observed decreases in the Tc up to 30 K in nanocomposite melt-spun ribbons of 2-14-1 and α-Fe. The starting materials contain about 6.5%–15% additional Fe, while some samples had 3 wt % Ti–C added to control grain growth. Spin reorientation temperatures Ts measured on the samples with or without Ti–C are from 120 to 122 K depending on the wheel speed and composition, suggesting that changes in Tc are due to microstructure. X-ray diffraction dilatometry using the α-Fe lattice suggests that at 300 K the iron is under tension but switches sign due to differences in coefficients of thermal expansion between the α-Fe and 2-14-1. Similar d spacing of the (110) of α-Fe and (006) of 2-14-1 suggest that changes in Tc may in part be due to epitaxial stresses affecting the exchange coupling in the nanocomposite alloys.

Crystallization behavior and magnetic properties of the low rare-earth content (Nd=6 at. %) Nd–Fe–Co–V–B nanocomposite magnet ribbons prepared by rapid quenching method

The low rare-earth content α-Fe/Nd2Fe14B nanocomposite magnets having a high soft phase ratio were fabricated by the rapid quenching method and evaluations were made of the crystallization behavior, microstructure, and magnetic properties in the annealing process. An investigation of the relationship between the roller surface velocity, Vs, and magnetic properties showed that changes in the crystal grain size of the α-Fe phase following annealing could be attributed to differences in the amorphous content of the as-melt-spun ribbons. As the amorphous content was increased, their crystal grain size tended to become finer and their magnetic properties tended to improve. However, it was observed that the optimum rapid quenching rate exists. The slight presence of clusters in as-melt-spun ribbons is favorable for obtaining good magnetic properties because the growth of α-Fe crystals is inhibited. The presumed reason for this inhibiting effect is that α-Fe growth occurs in a process in which clusters containing Nd expel this element. In the case of a completely amorphous state, large crystals grew easily, because they consisted of only Fe and Co in the initial stage.

Magnetic properties, Mössbauer and aftereffect studies of Pr10Fe90−xBx (x=5.88–11.5) nanocomposites

Magnetic properties, phase evolution and aftereffect of melt-spun Pr10Fe90−xBx (x=5.88–11.5) nanocomposite ribbons have been studied. Summarizing the results of thermal magnetic analysis and Mössbauer spectroscopy, two phases, namely Pr2Fe14B and α-Fe, were found for ribbons with x=5.88 and 7.5, while additional two metastable phases, Pr2Fe23B3 and Fe3B, prevailed for x=9. For x=10 and 11.5, only three of these phases: Pr2Fe14B, Pr2Fe23B3, and Fe3B, but not α-Fe were present. The optimal magnetic properties of Br=10.1 kG, Hci=6.4 kOe, and (BH)max=16.1 MGOe were achieved in the Pr10Fe84.12B5.88 ribbon, while Hci 8.71 kOe and (BH)max 14.7 MGOe were obtained in Pr10Fe80B10. Furthermore, Pr10Fe78.5B11.5 having the optimal Hci (9.33 kOe) exhibited minimum values in activation volume V=5.03×10−19 cm3, because it possessed the least volume fraction of the magnetically soft phases. Finally, confirmation of the absence of spin reorientation in Pr2Fe14B down to 5 K assures its advantage over Nd2Fe14B for low-temperature applications.

Magnetic properties and Mössbauer studies of Pr yFe 90− yB 10 ( y=8–11.76) nanocomposites

Magnetic properties and phase evolution of melt spun Pr y Fe 90− y B 10 ( y=8–11.76) nanocomposite ribbons have been studied. Based on TMA measurements and a Mössbauer analysis, four phases, Pr 2Fe 14B, Pr 2Fe 23B 3, Fe 3B and α-Fe, were found for y=8–9.5 and three phases, Pr 2Fe 14B, Pr 2Fe 23B 3 and Fe 3B, for y=10. For y=11.76, only the phase Pr 2Fe 14B was detected. An exchange coupling effect (evidenced by a Henkel plot) was found, to exist in all the ribbons if a suitable crystallization treatment was employed. In this study, optimal values for B r=9.6 kG, i H c=8.3 kOe and ( BH) max=16.2 MGOe were achieved in Pr 9.5Fe 80.5B 10. They result from a proper combination of magnetic phases in the ribbons.

Influence of Zr and Nb dopant additions on the microstructure and magnetic properties of nanocomposite RE2(Fe,Co)14B/α(Fe,Co) (RE=Nd–Pr) alloys

Nanocomposite REFeB alloy ribbons based on Nd/Pr rare earth (RE) mixtures were produced by devitrification of amorphous melt spun alloys. The effect of Zr and Nb dopant additions on the microstructures and magnetic properties of two-phase RE2Fe14B/α-Fe alloy ribbons are reported, the aim being to refine the α-Fe grain size with the refractory metal addition through retardation of the crystal growth rate. For the Zr-containing alloys (REyFe94−y−zZrzB6, y=8,10,z=0–4) only modest improvements of the magnetic properties, in comparison with the Zr-free alloys, were achieved for 8at% RE ribbon while, for 10% RE 2% Zr ribbon, fairly good combinations of intrinsic coercivity iHc (∼400kA/m) and maximum energy product (BH)max (∼130kJ/m3) were achieved. Improved grain refinement was achieved with the Nb addition, though the magnetic properties were broadly comparable with those for Zr doped alloys. Both Zr and Nb doping, however, resulted in a steep decrease in Curie temperature, reflecting an attenuation of the exchange interactions in the 2/14/1 unit cell. Additional substitution of 10% of the Fe by Co for the Nb doped alloy resulted in enhanced Tc, more than compensating for the reduction due to the Nb, and resulting also in an excellent combination of iHc (∼500kA/m) and (BH)max (140kJ/m3).

The combined effects of Ga, Nb, Zr, Hf, Pr on the magnetic properties and microstructure of (Nd, Pr)9(Fe, Ga, Nb, Zr, Hf)86.5B4.5 nanocomposite ribbons

The combined effects of Ga, Nd, Zr, Hf and Pr, used as additives, on the hard magnetic properties and microstructure of nanocomposite Nd9−xPrxFe86.5−y−z−m−nGayNbzZrmHfnB4.5 (x=0, 2.25; y, z, m, n=0.5, 1) ribbons were investigated by a L16(215) orthogonal experiment. All the ribbons were melt spun at 15 m/s and then annealed at 700°C for 15 min. The results show that strong interactions among these elements exist. Evidence has been found that increasing x and y, decreasing m and n and ensuring the proper concentration of Nb (0.5 at.%) can greatly improve (BH)max. The highest (BH)max of 124 kJ m−3 was obtained in Nd2.25Pr6.75Fe84.5Ga1.5Nb0.5B4.5. Furthermore, X-ray diffraction (XRD) and atomic force microscopy (AFM) were also used to investigate the effects of alloying elements on the microstructure and it was found that increasing the number and concentrations of alloying elements tends to promote amorphous phase formation and reduce the grain size markedly. The AFM observations are consistent with the XRD analysis, which suggests that AFM is a very useful and convenient tool for the observation of the microstructure of the ribbons.

低希土類組成（Ｎｄ＝６ａｔ．％）Ｎｄ‐Ｆｅ‐Ｃｏ‐Ｖ‐Ｂ系ナノコンポジット磁石薄帯の磁気特性と結晶化挙動

The magnetic properties and crystallization behavior of low-rare-earth-content (Nd = 6 at.%) α-Fe/Nd2Fe14B-type Nd-Fe-Co-V-B system nanocomposite magnet ribbons prepared by rapidly quenching with a single roller were investigated. The roller surface velocity VS of the rapid quenching directly affected on the amorphous volume and the magnetic properties after annealing. The formation of an Fe3B-like phase at an early stage of the crystallization process resulted in the reduction of the soft α-Fe phase grain size, and this brought about good magnetic properties.

The influence of Tb substitution on the magnetic properties of nanocomposite Pr/sub 2/Fe/sub 14/B/α-Fe magnets

Tb-doped (Pr,Tb)/sub 2/Fe/sub 14/Be//spl alpha/-Fe nanocomposite ribbons have been synthesized by melt-spinning Pr/sub 8-x/Tb/sub x/Fe/sub 86/B/sub 6/ alloys at low speeds. The effects of Tb substitution and rapid annealing on the magnetic properties of the composites were investigated. With a small addition of Tb, the Curie temperature of hard phase increases slightly, the saturation magnetization decreases but the coercivity increases due to a higher anisotropy field and a refinement of grain size, leading to an enhancement in the energy product. Transmission electron microscopy revealed a finer and more homogeneous (Pr,Tb)/sub 2/Fe/sub 14/B//spl alpha/-Fe microstructure with an average grain size in the range from 20 to 40 nm. The best results are obtained with a room temperature coercivity of 6.6 kOe, M/sub r/=118 emu/g, and (BH)/sub m/=15.2 MGOe in Pr/sub 7/Tb/sub 1/Fe/sub 86/B/sub 6/ sample annealed at 800/spl deg/C for 1 minute.

Demagnetization behaviour in exchange-coupled Pr10Fe85B5 ribbons

Nanocomposite Pr10Fe85B5 ribbons, mainly composedof Pr2Fe14B and α-Fe, were prepared by melt spinning andsubsequent annealing. Although a good single magnetic hard phase behaviourwas observed in the demagnetization curve at room temperature, an obviousshoulder was found at low temperatures. A simple model, in which a softmagnetic moment was pinned at grain boundaries by the magnetic hard phase,was used to calculate the demagnetization curve of the magnetic softphase. The calculated results are in close agreement with experimentalobservations. The coercivity mechanism of the ribbons is discussed withrespect to intergrain exchange coupling.