Magnetic hardening mechanism in sintered R–Fe–B permanent magnets

After a short review on temperature dependence of the intrinsic coercivity in sintered Nd–Fe–B-type magnets is given, recent experimental results concerning the coercivity-anisotropy (HC–HA) correlation in B-rich Pr–Fe–B and Nd–Fe–B sintered magnets and the influence of the surface conditions of the sintered Nd–Fe–B magnets on the coercivity are reported. The results are interpreted in terms of the μoHc vs cμoHA – NIs plot, where Is is the spontaneous magnetization of R2Fe14B (R = Pr or Nd) and N is the effective demagnetization field coefficient.

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Magnetic Hardening Mechanism in Sintered R-Fe-B Permanent Magnets

MRS Proceedings ◽

10.1557/proc-96-161 ◽

1987 ◽

Vol 96 ◽

Cited By ~ 10

Author(s):

M. Sagawa ◽

S. Hirosawa

Keyword(s):

Permanent Magnet ◽

Permanent Magnets ◽

State Of The Art ◽

Spontaneous Magnetization ◽

Experimental Results ◽

Surface Conditions ◽

Hardening Mechanism ◽

Sintered Magnets ◽

Field Coefficient ◽

Magnetic Hardening

ABSTRACTThe state-of-the-art description of the magnetic hardening mechanism in the sintered Nd-Fe-B permanent magnet is given. Recent experimental results concerning the coercivity-anisotropy (Hc -HA) correlation in B-rich Pr-Fe-B and Nd-Fe-B sintered magnets and the inhluence of the surface conditions of the sintered Nd-Fe-B magnets on the coercivity are reported. These results are interpreted in terms of the μ0Hc versus cμ0 HA -NIS plot, where I is the spontaneous magnetization of R2 Fe14 (R=Pr or Nd) and N the effective demagnetization field coefficient.

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Evolution of intrinsic coercivity in Pt-Co-B alloys

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100121417 ◽

1992 ◽

Vol 50 (1) ◽

pp. 202-203

Author(s):

N. Qiu

Keyword(s):

Permanent Magnets ◽

Ternary Alloys ◽

Good Thermal Stability ◽

Hardening Mechanism ◽

Potential Applications ◽

Magnetic Hardening ◽

Rapidly Solidification ◽

Evolution Of Microstructure ◽

Rapidly Solidified ◽

Thermal Stability Of

New permanent magnets based on Pt-Co-B ternary alloys have been developed by rapidly solidification with subsequent heat treatments. The coercivity achieved in the Pt-Co-B ternary alloys is more than double the highest coercivity observed in the Pt-Co binary system. Good thermal stability of the coercivity produced by annealing provides a basis for consolidation processes such as hot isotropic pressing to produce bulk magnets from the rapidly solidified Pt-Co-B materials. Increased coercivity coupled with special properties such as high Curie temperature, corrosion resistance and ductility may expand the potential applications for these alloys. The evolution of microstructure and its effect on coercivity from annealing the as-quenched materials are investigated to understand the magnetic hardening mechanism and optimize the magnetic properties.

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Analysis of the magnetic hardening mechanism in RE-FeB permanent magnets

Journal of Magnetism and Magnetic Materials ◽

10.1016/0304-8853(88)90202-8 ◽

1988 ◽

Vol 74 (3) ◽

pp. 291-302 ◽

Cited By ~ 418

Author(s):

H. Kronmüller ◽

K.-D. Durst ◽

M. Sagawa

Keyword(s):

Permanent Magnets ◽

Hardening Mechanism ◽

Magnetic Hardening

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HIGHLY ANISOTROPIC MnBi MAGNETS

Vietnam Journal of Science and Technology ◽

10.15625/2525-2518/54/1a/11806 ◽

2018 ◽

Vol 54 (1A) ◽

pp. 58

Author(s):

Nguyen Van Vuong

Keyword(s):

Permanent Magnets ◽

Spontaneous Magnetization ◽

Mass Density ◽

Thermal Coefficient ◽

Energy Product ◽

Intrinsic Coercivity ◽

Oriented Parallel ◽

Two Parameters ◽

Bulk Magnet ◽

Compacting Pressure

The rare-earth-free MnBi magnetic material is promising for high-temperature (150 200 oC) application of permanent magnets because of its large magnetocrystalline energy and especially the positive thermal coefficient of coercivity (dHc/dT > 0). Because of the moderate value of the spontaneous magnetization Ms 74 emu/g, the anisotropy of MnBi bulk magnets should be investigated to enhance the remanence Mr. With large ratio Mr/Ms and appropriate microstructure, the squareness of MnBi magnets should have high value leading the remanent coercivity bHc close to the intrinsic coercivity iHc, thus enhancing the energy product (BH)max. The paper presents an approach to loading and compacting of MnBi powders in the 18 kOe magnetic field oriented perpendicular to the pressing direction where MnBi grains can be freely rotated and oriented parallel to the field direction. Based on the energy minimization of the assembly of magnetized grains, the compacting pressure was chosen to optimize two parameters, the mass density and the coercivity iHc of magnets. The prepared MnBi bulk magnet had 8.4 g/cm3, Mr/Ms 0.92, 0.89 and (BH)max reached 8.4 MGOe.

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Lorentz Electron Microscopy of cobalt borides in a platinum cobalt matrix

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010015109x ◽

1993 ◽

Vol 51 ◽

pp. 1052-1053

Author(s):

N. Qiu ◽

J.E. Wittig

Keyword(s):

Electron Microscopy ◽

Magnetic Domain ◽

Ion Milling ◽

Magnetic Domain Wall ◽

Hardening Mechanism ◽

Contrast Method ◽

Intrinsic Coercivity ◽

Cobalt Boride ◽

Magnetic Hardening ◽

Thickness Measurements

The presence of cobalt borides significantly increases the intrinsic coercivity (Hic) of a Pt-Co alloy. Whereas the maximum Hic for a binary Pt-Co alloy is less than 5 kOe, a ternary Pt42Co45B13 (at%) alloy exhibits intrinsic coercivity as large as 15.2 kOe. The optimum microstructure for the maximum Hic consists of a dispersion of cobalt boride precipitates having the orthorhombic Co3B structure in an Ll0 Pt-Co matrix. Lorentz electron microscopy of the magnetic structure of these cobalt borides has been used to elucidate their strong influence on the magnetic properties of this alloy. Magnetic domain wall thickness measurements assist with modeling of the magnetic hardening mechanism.Processing the Pt42Co45B13 (at%) material utilized an initial rapid solidification step followed by annealing at 800°C. Samples for Lorentz electron microscopy were prepared by dimple grinding and ion milling to electron transparency. The Lorentz imaging employed the standard Fresnel contrast method by operating a Philips CM20T at 200 kV in the low magnification (LM) mode.

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