The Exchange Energy Term and the Curling Reversal Mode in Hard Magnetic Materials Manufactured by Powder Metallurgy

The curling reversal mode is discussed, with emphasis on the assumptions of the model, many of them unrealistic. The curling mode assumes the Bloch approximation, where a cosine function is approximated by a polynomial of second order. It is argued that if the curling model takes place, this could affect the anisotropy field, and then the anisotropy field would be function of the grain size, but this is not observed. Exchange effects may affect hysteresis curve, as discussed in the SW-CLC model.

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Coercivity Mechanism in Hard and Soft Sintered Magnetic Materials

Materials Science Forum ◽

10.4028/www.scientific.net/msf.802.563 ◽

2014 ◽

Vol 802 ◽

pp. 563-568 ◽

Cited By ~ 1

Author(s):

Marcos Flavio de Campos

Keyword(s):

Grain Size ◽

Domain Wall ◽

Magnetic Materials ◽

Wall Thickness ◽

Magnetic Behavior ◽

Soft Magnetic Materials ◽

High Coercivity ◽

Soft Magnetic ◽

Hard Magnetic Materials ◽

Wall Movement

The coercivity in soft and hard magnetic materials has different origin. The high coercivity of barium ferrite, SmCo5, Sm2Co17or Nd2Fe14B is due to high magnetocrystalline anisotropy, and the processing aims very small grain size (nanocrystalline). In the case of soft magnetic materials, the coercivity has origin in defects that are able to stop domain wall movement, as for example grain boundaries, inclusions or dislocations. Soft magnetic materials in general present large domain wall thickness (thousands of Angstroms for pure iron), whereas domain wall thickness is ~ 50 Angstroms for SmCo5and Nd2Fe14B. The differences between hard and soft magnetic behavior are commented and discussed. The domain wall energy and thickness can be used as parameters for classifying soft and hard magnetic behavior. Other examples of soft magnetic materials are the amorphous alloys and the nanocrystalline soft magnetic materials with grain size very below the single domain particle size. The soft behaviour in amorphous and soft nanocrystalline materials is also discussed.

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Magnetic materials

10.1093/oso/9780198829942.003.0011 ◽

2018 ◽

Author(s):

L. Solymar ◽

D. Walsh ◽

R. R. A. Syms

Keyword(s):

Quantum Theory ◽

Magnetic Resonance ◽

Magnetic Materials ◽

Domain Walls ◽

Ferromagnetic Materials ◽

Hysteresis Curve ◽

Magnetic Polarization ◽

Hard Magnetic Materials ◽

Resonance Phenomena ◽

Quantum Theory Of Magnetism

Macroscopic and microscopic theories of magnetic polarization are discussed. The origin of domains, domain walls, and of the hysteresis curve and the contrast between soft and hard magnetic materials are explained. The more important elements of the quantum theory of magnetism are discussed. The principles of the alignments in antiferromagnetic and ferromagnetic materials are explained. Magnetic resonance phenomena are discussed. Magnetoresistance and spintronics and their device prospects are also discussed at some length.

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Simulating the Hysteretic Characteristics of Hard Magnetic Materials Based on Nd2Fe14B and Ce2Fe14B Intermetallics

Crystals ◽

10.3390/cryst10060518 ◽

2020 ◽

Vol 10 (6) ◽

pp. 518 ◽

Cited By ~ 1

Author(s):

Natalia B. Kolchugina ◽

Mark V. Zheleznyi ◽

Aleksandr G. Savchenko ◽

Vladimir P. Menushenkov ◽

Gennadii S. Burkhanov ◽

...

Keyword(s):

Magnetic Anisotropy ◽

Magnetic Materials ◽

Permanent Magnets ◽

Mixed Valence ◽

Hysteresis Loops ◽

Anisotropy Field ◽

Spin Reorientation ◽

Cost Ratio ◽

Hard Magnetic Materials ◽

Negative Effect

The Ce2Fe14B intermetallic, like Nd2Fe14B, has the tetragonal Nd2Fe14B-type structure (space group P42/mnm), in which Ce ions have a mixed-valence state characterized by the coexistence of trivalent 4f1 and tetravalent 4f0 electron states. Despite the fact that the saturation magnetization, magnetic anisotropy field, and Curie temperature of the Ce2Fe14B intermetallic are substantially lower than those of Nd2Fe14B and Pr2Fe14B, Ce2Fe14B retains the capacity of being able to be used in the manufacturing of rare-earth permanent magnets. Moreover, at low temperatures, the anisotropy field of Се2Fe14B is higher than that of Nd2Fe14B, and Се2Fe14B does not undergo the spin-reorientation transition. In this respect, studies of (Nd, Ce)-Fe-B alloys, which are intended for the improvement of the service characteristics-to-cost ratio, are very relevant. A model and algorithm for calculating the hysteresis loops of uniaxial hard magnetic materials with allowance for the K1 and K2 (K2 > 0 and K1 > 0 and K1 < 0) magnetic anisotropy constants were developed and allowed us to obtain data on their effect on the parameters of hysteresis loops for a wide temperature range (0–300 K). The simulation and analysis of hysteresis loops of the quasi-ternary intermetallics (Nd1−хСех)2Fe14B (х = 0–1) was performed. Results of the simulation indicate that the alloying of the Nd2Fe14B intermetallic with Ce to x = 0.94 (1) does not completely eliminate the negative effect of spin-reorientation phase transition on the residual magnetization of the (Nd1−хCeх)2Fe14B intermetallic and (2) slightly decreases the slope of magnetization reversal curve.

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Study on the erosion of Mo/ZrO2 alloys in glass melting process

High Temperature Materials and Processes ◽

10.1515/htmp-2020-0061 ◽

2020 ◽

Vol 39 (1) ◽

pp. 595-598

Author(s):

Cui Chaopeng ◽

Zhu Xiangwei ◽

Li Qiang ◽

Zhang Min ◽

Zhu Guangping

Keyword(s):

Grain Size ◽

Corrosion Resistance ◽

Powder Metallurgy ◽

Hydrothermal Synthesis ◽

Grain Boundaries ◽

Electrode Material ◽

Glass Melting ◽

Melting Process ◽

Fine Grain ◽

Conventional Electrode

AbstractThe Mo/ZrO2 electrode was prepared by combining hydrothermal synthesis with powder metallurgy, and this new electrode material has a totally different microstructure from the conventional electrode. The grain size of the new electrode was fine, and the size of ZrO2 in the alloy reached 200 nm. According to the results, the Mo–ZrO2 electrode has better performance, because the erosion occurs along the grain boundaries. Meanwhile, the new electrode, based on its fine grain, can effectively improve the corrosion resistance of the electrode.

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Powder metallurgy of the porous Ti-13Nb-13Zr alloy of different powder grain size

Materials and Manufacturing Processes ◽

10.1080/10426914.2019.1605178 ◽

2019 ◽

Vol 34 (8) ◽

pp. 915-920 ◽

Cited By ~ 1

Author(s):

Tomasz Seramak ◽

Andrzej Zielinski ◽

Waldemar Serbinski ◽

Katarzyna Zasinska

Keyword(s):

Grain Size ◽

Powder Metallurgy ◽

Porous Ti ◽

13Zr Alloy

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Competition of two terms in exchange energy (A=A1+A2) for magnetic materials

Solid State Communications ◽

10.1016/s0038-1098(02)00494-5 ◽

2002 ◽

Vol 124 (5-6) ◽

pp. 215-219 ◽

Cited By ~ 1

Author(s):

Yongzhong Wang ◽

Zhidong Zhang

Keyword(s):

Magnetic Materials ◽

Exchange Energy

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Nucleation fields and grain boundaries in hard magnetic materials

IEEE Transactions on Magnetics ◽

10.1109/20.281083 ◽

1993 ◽

Vol 29 (6) ◽

pp. 2878-2880 ◽

Cited By ~ 34

Author(s):

T. Schrefl ◽

H.F. Schmidts ◽

J. Fidler ◽

H. Kronmuller

Keyword(s):

Grain Boundaries ◽

Magnetic Materials ◽

Hard Magnetic Materials

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Local Density Approximations for the Energy of a Periodic Coulomb Model

Mathematical Models and Methods in Applied Sciences ◽

10.1142/s0218202503002866 ◽

2003 ◽

Vol 13 (08) ◽

pp. 1185-1217 ◽

Cited By ~ 9

Author(s):

Olivier Bokanowski ◽

Benoît Grebert ◽

Norbert J. Mauser

Keyword(s):

Kinetic Energy ◽

Local Density ◽

Exchange Energy ◽

Asymptotic Approximations ◽

Exchange Potential ◽

Energy Term ◽

Local Exchange ◽

Coulomb Model ◽

Local Density Approximations ◽

Number Of Particles

We deal with local density approximations for the kinetic and exchange energy term, ℰ kin (ρ) and ℰ ex (ρ), of a periodic Coulomb model. We study asymptotic approximations of the energy when the number of particles goes to infinity and for densities close to the constant averaged density. For the kinetic energy, we recover the usual combination of the von-Weizsäcker term and the Thomas–Fermi term. Furthermore, we justify the inclusion of the Dirac term for the exchange energy and the Slater term for the local exchange potential.

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