Squareness Of Demagnetization Curve Research Articles

Hard Magnetic Property Improvement of Melt-Spun PrCo5 Ribbons by Fe and C Doping

Magnetic properties and microstructure of melt-spun PrCo5− x − y Fe x C y ( x = 0 and 0.3; y = 0–0.3) ribbons are studied. For PrCo5 ribbons spun at lower wheel speed of 20 m/s, the coexistence of 2:17 phase with magnetic hard 1:5 phase leads to low coercivity of 0.6 kOe. Increasing wheel speed to 40 m/s imroves the coercivity to 3.3 kOe due to the increased volume fraction of 1:5 phase. Interestingly, magnetic properties of PrCo5 ribbons melt spun at 40 m/s ( Br = 6.4 kG, i H c = 3.3 kOe, and ( BH )max = 4.5 MGOe) are improved to Br = 6.1–6.5 kG, i H c = 7.8–13.5 kOe, ( BH )max = 7.3–8.9 MGOe by doping C, and significantly enhanced to Br = 6.3 kG, i H c = 16.1 kOe, and ( BH )max = 9.3 MGOe for C and Fe co-doped PrCo4.6Fe0.3C0.1 ribbons. The structural and thermo-magnetic analysis confirms that the entrance of Fe and part of C into the crystal structure of 1:5 phase leads to the increase of Curie temperature. Doping proper C content not only uniformly refines grain size and, therefore, improves the squareness of demagnetization curve and ( BH )max, but also increases the volume fraction of 1:5 phase, and thus enhances the coercivity. The increased volume fraction of 1:5 phase and the reduced magnetic domain size due to refined microstructure by co-doping Fe and C make PrCo4.6Fe0.3C0.1 ribbons exhibit a high permanent magnetic performance. They are promising candidate materials for making bonded magnets.

Magnetic Property Enhancement of Melt Spun YCo5 Ribbons by Fe and C Doping

Magnetic properties and microstructure of melt spun YCo5– x – y Fe x C y ( $x = 0$ –0.3 and $y = 0$ –0.3) ribbons are studied. Magnetic properties of YCo5 ribbons ( i H c = 144 kA/m and (BH) $_{\max } = 16.8$ kJ/m3 are slightly improved to i H c = 160–224 kA/m and (BH) $_{\max } = 21.6$ –27.2 kJ/m3 by Fe-doping, and are increased to i H c = 560–1128 kA/m and (BH) $_{\max }= 42.4$ –51.2 kJ/m3 by C-doping, respectively. Most interestingly, the optimal (BH) $_{\max }$ of 72.8 kJ/m3 with high i H c of 1200 kA/m achieved for Fe and C-co-doped YCo4.6Fe0.3C0.3 ribbons is the highest value in Y–Co alloy ribbons ever reported. The structural and thermo-magnetic analysis confirm that Fe and C enter the YCo5 (5:1) crystal structure and lead to the increase of Curie temperature. Besides, C-doping uniformly refines grain size and, therefore, improves the squareness of demagnetization curve and (BH) $_{\max }$ . The formation of YCo, Fe)5C x phase and the microstructure refinement are the main reasons to result in the enhancement of hard magnetic properties for the YCo4.4Fe0.3C0.3 ribbons. The presented results suggest that the YCo5 ribbons optimized by co-doping with Fe and C are promising candidate materials for making bonded magnets.

Comparison of Demagnetization Curve of Nd‐Fe‐B Magnets Measured with Various Magnetization Measurement Systems

SUMMARYThe magnetic properties of Nd‐Fe‐B magnets with 0.5 mm and 1 mm cubes in size were measured with a vibrating sample magnetometer equipped with high‐temperature superconducting magnet (VSM_HSC). With the VSM_HSC, high sweep speed and high accuracy in magnetization measurement were achieved. Furthermore, magnetic properties of Nd‐Fe‐B magnets were measured with the VSM_HSC, pulsed field magnetometer, and a permeameter. It was found that the squareness of demagnetization curves appeared depending on the measurement systems.

Coercivity enhancement in (Ce,Nd)-Fe-B sintered magnets prepared by adding NdHx powders

(Ce,Nd)-Fe-B sintered magnets were prepared by the addition of NdHx powders in Ce9Nd4.5Fe80B6.5 powders. The coercivity is rather low in Ce9Nd4.5Fe80B6.5 magnets, and Ce element prefers to distribute at the outer-layer of main phase (Ce,Nd)2Fe14B. The investigation of scanning electron microscope shows that the addition of NdHx powders leads to the increase of Nd content at grain outer-layer of main phase owing to the element diffusion. Magnetization reversal undergoes the nucleation of reversed domain wall at grain outer-later, and the addition of NdHx powders leads to the increase in the nucleation field of reversed domain, giving rise to the significant improvement of coercivity. The larger amount addition of NdHx powders leads to the increase in the amount of intergranular phase, resulting in the decreases of the remanence, the squareness of demagnetization curve and the maximum energy product.

280 kJ/m<sup>3</sup>高鉄濃度サマリウムコバルト磁石の開発・実用化

We have developed Sm2Co17 sintered magnets whose Fe concentration is much higher than conventional Sm2Co17 sintered magnets. The pre-aging treatment leads to fine cell structure and improvement in squareness of demagnetization curves. As a result the (BH)max of pre-aged magnets shows higher than that of no-pre-aged magnet. The inter-mediate heat treatment (IHT) induces the grain growth. We found that squareness of demagnetization curve has clearly improved by the IHT at adequate temperature. These results indicate that reducing the fraction of grain boundaries by increasing the grain size affects the behavior of domain-wall motion. Sm2Co17 sintered magnets fabricated adopting pre-aging treatment and IHT show (BH)max of 282 kJ/m3.

Influence of Nd Doping on the Magnetic Properties of Nd<sub>2</sub>Fe<sub>14</sub>B/α-Fe Nanocomposite Magnets

Soft magnetic alloys Fe95Nd5and Fe89.5Nd10.5were made by the mechanically ball milling to investigate the influence of Nd doping on the magnetic properties of Nd2Fe14B/α-Fe nanocomposite magnets. The coercivity was enhanced with increasing Nd of the pre-alloyed Nd-Fe soft powders. The further discussions on Nd2Fe14B/α-Fe nanocomposite were also carried out through directly mixing the pure Nd as the interface improving agent. Compared with Nd-Fe pre-alloys, the direct addition of Nd was more favorable to reinforce the coercivity of nanocomposite magnets and the squareness of demagnetization curve, thereby increasing the maximum magnetic energy product.

Structure and magnetic properties of Pr2Fe14(C, B)/α-(Fe, Co)-type nanocomposite ribbons

The phase evolution, microstructure and magnetic properties of PrxFe82-x-yTiyCo10B4C4 (x=9—10.5; y=0, 2) melt-spun ribbons have been investigated. All ribbons are mainly comprised of the 2 ∶14 ∶1, 2 ∶17 and α-(Fe, Co) phases. For the group of Ti-free ribbons (y=0), the coercivity increases with increasing x while the remanence decreases with increasing x. When 2 at.%Ti is substituted for Fe in the Ti-free ribbons, the magnetic properties are remarkably enhanced. The coercivity and squareness of demagnetization curve of the Ti-substitution ribbons are substantially improved without a sacrifice of remanence (except for x=9), the remanence even obviously increases at x=10.5. The optimal magnetic properties of Br=9.6 kGs (1 Gs=10-4T), iHc =10.2 kOe (1 Oe=79.5775 A/m), (BH)max＝17.4 MGOe have been obtained in Ti-substituted Pr10.5Fe69.5Ti2Co10B4C4 group. The volume fraction of the 2 ∶14 ∶1 phase increases with increasing x, which leads to an increase of coercivity. Ti-substitution suppresses the grain growth of α-(Fe, Co) phase during annealing process, which makes the volume ratio of magnetically hard phase and soft phase and grain size tend to have optimal values, and the intergranular exchange coupling substantially enhances.

Magnetic properties and thermal stability of anisotropic bonded Nd-Fe-B magnets by warm compaction

Anisotropic bonded magnets were prepared by warm compaction using anisotropic Nd-Fe-B powder. The forming process, magnetic properties, and temperature stability were studied. The results indicate that the optimal temperature of the process, which was decided by the viscosity of the binders, was 110°C. With increasing pressure, the density of the magnets increased. When the pressure was above 700 MPa, the powder particles were destroyed and the magnetic properties decreased. The magnetic properties of the anisotropic bonded magnets were as follows: remanence Br = 0.98 T, intrinsic coercivity iHc=1361 kA/m, and maximum energy product BHmax = 166 kJ/m3. The magnets had excellent thermal stability because of the high coercivity and good squareness of demagnetization curves. The flux density of the magnets was 35% higher than that of isotropic bonded Nd-Fe-B magnets at 120°C for 1000 h. The flux density of the bonded magnets showed little change with regard to temperature.

Effects of machining on the magnetic properties of sintered NdFeB magnets

Effects of mechanical machining on the magnetic properties of small NdFeB magnets were investigated by pulsed field magnetometry. Unlike the large sample, the small magnets machined by spark wiring, diamond cutting and hand grinding showed a kink on the second quadrant of demagnetization curves. The breaking samples resulted in no kink because the cleavage fracture characteristics along grain boundary conserves the Nd 2 Fe 14 B grains from mechanical damage. Annealing the machined samples at 200 and 300 °C recovered coercivity to some extent, and the elimination of machined surface by chemical etching increased remanence and squareness of demagnetization curve. However, the kink on demagnetzation curve did not disappear by annealing and chemical etching.

Magnetic properties and microstructures of mischmetal-FeB-(Al, Ti and Al-Co) permanent magnets

The magnetic characteristics of anisotropic MM-FeB- (Al, Ti and Al-Co) permanent magnets have been investigated by using hot-pressing and die-upsetting process. The best magnetic properties obtained in these studies were HC = 5.1 kOe, Br = 5.4 kG with (BH)max = 5.1 MGOe for hot-pressed MM-FeB-Al-Co magnets and HC = 3.6 kOe, Br = 6.7 kG, (BH)max = 6.8 MGOe for die-upset MM-FeB-Al-Co magnets. Higher squareness of demagnetization curve was obtained in anisotropic die-upset MM-FeB- (Al, Al-Co) magnets. X-ray diffraction and STEM investigations revealed that the higher magnetic properties in die-upset magnets were resulted from alignment of the c-axis along the die-upsetting direction. The magnetic anisotropy of the die-upset magnets and the densification of the hot-pressed magnets were increased by partial substitution of Al and Al-Co for Fe.

Magnetic Properties of Thin Compacted and Sintered Nd-Fe-B-Type Magnets

The granulation of Nd-Fe-B powder was investigated by the spray-drying method, using poly (vinyl alcohol) as a binder to give it good flowability. The amount of oxygen and carbon in sintered magnets can be controlled below the upper limit by cooling the slurry and debinding green compacts in a hydrogen atmosphere. As the granulated Nd-Fe-B powder has good flowability, thin green compacts can be easily produced from it, and the sintered bodies are highly accurate in size. Micro-ring magnets with a thickness of 0.6 mm and thin-plate magnets with a thickness of 0.2 mm were successfully synthesized by spray-dried Nd-Fe-B powder without any serious damage to the surfaces by oxidation, which harms coercivity and the squareness of demagnetization curve.