The best starting materials for die‐upset magnets are moderately overquenched melt‐spun ribbons of Nd‐Fe‐B alloys with ∼20 at. % more rare earth than stoichiometric Nd2Fe14B. Remanence increases with increasing die‐upset (DU) level, reaching a maximum of 13.5 kG at 70% DU for ternary Nd‐Fe‐B magnets, beyond which cracking limits performance. Remanence is also limited by nonuniform deformation, particularly for moderately die‐upset magnets. Heat treatments, dysprosium substitutions, or low‐level additives can be used to compensate for the decreases in coercivity which accompany increases in die‐upset level. By die upsetting in stages and removing misaligned surfaces, a large Nd‐Fe‐Co‐B‐Ga magnet (∼30 g) has been produced with both a high remanence (14.2 kG) and a high‐energy product (48.5 MG Oe).

High‐remanence rapidly solidified Nd‐Fe‐B: Die‐upset magnets (invited)

In this study, α-Fe/Nd2Fe14B nanocomposite magnets with strong crystallographic texture were prepared by controlled melt spinning. For a relatively low wheel speed of 10 m/s, the c-axis texture of the Nd2Fe14B crystals is predominantly perpendicular to the plane of the ribbon, but it switches to parallel to the ribbon plane direction at a higher wheel speed of 20 m/s. The magnets show strong magnetic anisotropy between in and out of the ribbon planes. High remanence of 0.74Ms and a large energy product of 24.3 MGOe were observed parallel to the ribbon plane direction in the magnets prepared at a wheel speed of 20 m/s.

Crystallographic texture and magnetic anisotropy of α-Fe/Nd2Fe14B nanocomposites prepared by controlled melt spinning

Melt-spun magnetically anisotropic SmCo5 ribbons with high permanent performance

Magnetic properties and microstructures of Pr-Fe-B-(Ga) melt-spun ribbons prepared by single or twin rollers have been studied. Strong intensities of

Anisotropic Pr-Fe-B melt-spun ribbons

Sm(CobalFe0.1Cu0.1Zrw)7 (w=0.01−0.09) ribbons have been prepared by conventional melt spinning followed by precipitation hardening. The Zr addition can suppress the nucleation of solidification and increase the velocity of grain growth. This leads to the increase of texture degree of the ribbons with increasing Zr content. The crystallographic texture is still preserved in ribbons after the precipitation hardening. The remanence ratio of the heat-treated ribbons increases from 0.7 for w=0.01 to 0.9 for w=0.08. An energy product of about 10 MGOe has been obtained in the ribbon with w=0.03. The angular dependence of coercivity suggests that the magnetization reversal of the precipitation-hardened ribbons is controlled by both domain-wall pinning and nucleation mechanism.

Effect of Zr on the crystallographic texture of precipitation-hardened Sm(Co,Fe,Cu,Zr)7 ribbons

Rapid solidification by twin‐roller quenching of iron‐neodymium‐boron alloys produces flakes which show a strong (00l) texture normal to their surface by x‐ray diffraction. The strong crystal orientation is argued to be due to both directional solidification in a thermal gradient and uniaxial deformation of the solid phase in the twin rollers. Magnetization studies on individual flakes show intrinsic coercivities of 14 kOe and a nearly 50% higher remanance for field normal to the flake surface (Br =9.5 kG) than in the flake plane (Br =6.5 kG). The perpendicular (BH)max is 16 MG Oe.

Nicholas J. Grant

Papers

Magnetic anisotropy of Nd15Fe77B8 flakes made by twin-roller quenching