Initial Magnetization Behavior of Rapidly Quenched Neodymium-Iron-Boron Magnets

1987 ◽  
Vol 96 ◽  
Author(s):  
F. E. Pinkerton
Keyword(s):  
Grain Size ◽  
Domain Wall ◽  
Domain Walls ◽  
Initial Permeability ◽  
Single Domain ◽  
Initial Magnetization ◽  
Domain Wall Pinning ◽  
Rapidly Solidified ◽  
Coercivity Mechanism ◽  
Magnetization Behavior

ABSTRACTInitial magnetization and demagnetization data are reported for three forms of rapidly solidified Nd-Fe-B permanent magnet materials: melt-spun ribbons, hot pressed magnets, and die upset magnets. In all three materials the results are consistent with domain wall pinning at grain boundary phases as the coercivity mechanism. Optimally quenched ribbons are comprised of randomly oriented single domain Nd2Fe14B grains, and both initial magnetization and demagnetization are controlled by strong domain wall pinning at grain boundaries. Maximum coercivity is accompanied by a low initial permeability. Coercivity is reduced in overquenched ribbons by partial retention of a magnetically soft amorphous or very finely crystalline microstructure. Coercivity decreases in underquenched ribbons because wall pinning weakens as the grain size increases above optimum. Correlation of magnetization and demagnetization behaviors suggests that maximum coercivity in ribbons is largely determined by the resistance to domain wall formation in grains smaller than the single domain particle limit. Grain size is much less important in the aligned die upset magnets. Domain walls are initially free to move until they become strongly pinned at grain edges, and complete magnetization requires an applied field greater than the coercive field. Hot pressed magnets show a mixture of ribbon and die upset behavior.

Relation between Initial Magnetization Curve and Grain Size of Nanocrystalline NdFeB Magnets

2014 ◽  
Vol 802 ◽  
pp. 558-562 ◽  
Author(s):  
Marcos Flavio de Campos ◽  
Fernanda A.S. da Silva ◽  
José Adilson de Castro
Keyword(s):  
Grain Size ◽  
Magnetization Curve ◽  
Volume Fraction ◽  
Domain Size ◽  
Single Domain ◽  
Ndfeb Magnets ◽  
Initial Susceptibility ◽  
Initial Magnetization ◽  
Coercivity Mechanism

The volume fraction of the single domain size particles can be directly estimated from the initial magnetization of thermally demagnetized magnets. Multi-domain grains present initial magnetization curve with high initial susceptibility, whereas single-domain grains present low susceptibility initial magnetization curve. In the case of single domain size particles, the coercivity mechanism is coherent rotation and the Stoner-Wohlfarth (SW) model can be applied. From the initial magnetization curve of magnets, the volume fraction of grains with diameter less than 0.3 micrometers can be estimated in NdFeB magnets. This is possible because the Nd2Fe14B phase is single domain below 0.3 micrometers.

Intrinsic domain wall pinning in rapidly solidified amorphous nanowires

2014 ◽  
Vol 115 (17) ◽  
pp. 17A329 ◽  
Author(s):  
T.-A. Óvári ◽  
H. Chiriac
Keyword(s):  
Domain Wall ◽  
Domain Wall Pinning ◽  
Rapidly Solidified

Morphology and Domain Structure of Unsupported PbTiO3Thin Films Prepared by Sol-Gel Process

1995 ◽  
Vol 403 ◽  
Author(s):  
C. J. Lu ◽  
S. B. Ren ◽  
H. M. Shen ◽  
Y. N. Wang
Keyword(s):  
Thin Films ◽  
Grain Size ◽  
Domain Structure ◽  
Domain Walls ◽  
Sol Gel ◽  
Single Domain ◽  
Annealing Temperatures ◽  
Sol Gel Process ◽  
Size And Morphology ◽  
Almost All

AbstractThe morphology and domain structure of unsupported PbTiO3thin films with fine grains (>200 nm) were investigated by TEM technique. The unsupported PbTiO3thin films were successfully prepared by sol-gel process onto NaCI substrates and followed by dissolving away the substrates. Electron diffiraction patterns showed that the unsupported PbTiO3thin films had slight <110> preferred orientation perpendicular to the film surfaces. Grain size and morphology vary significantly with the thickness of the films or the annealing temperatures. Even though the grain size is rather small (40–180 nm), the domains are clearly visible. Most of the grains show single domain, while some irregular and curved domain walls appear only in a small portion of the fine grains. The number of single-domained grains increases with decreasing grain size. Almost all domain walls observed are 90° walls.

Mechanisms of Pinning of Domain Walls in Nanowires

2010 ◽  
Vol 168-169 ◽  
pp. 230-233 ◽  
Author(s):  
A.A. Ivanov ◽  
V.A. Orlov ◽  
N.N. Podolsky
Keyword(s):  
Numerical Methods ◽  
Domain Wall ◽  
Coercive Force ◽  
Magnetization Curve ◽  
Domain Walls ◽  
Magnetostatic Interaction ◽  
Crystallographic Anisotropy ◽  
Domain Wall Pinning ◽  
Force Profile ◽  
Pinning Of Domain Walls

Analytical and numerical methods are used to study the process of motion of domain walls in an individual nanowire consisting of ferromagnetic crystallites with a chaotic crystallographic anisotropy. The influence of magnetostatic interaction on the motion is considered. The force profile of the domain wall pinning, caused by stochastic crystallographic anisotropy, is examined. The magnetization curve is analytically constructed and the coercive force is calculated. The Barkhausen jumps of domain walls are investigated. The result is verified by numerically modeling.

scholarly journals Unconventional magnetization textures and domain-wall pinning in Sm–Co magnets

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Leonardo Pierobon ◽  
András Kovács ◽  
Robin E. Schäublin ◽  
Stephan S. A. Gerstl ◽  
Jan Caron ◽  
...  
Keyword(s):  
Domain Wall ◽  
High Performance ◽  
Domain Walls ◽  
Atom Probe ◽  
Electron Holography ◽  
Micromagnetic Simulations ◽  
Transmission Electron ◽  
Domain Wall Pinning ◽  
Weak Points ◽  
Magnetic Hardness

AbstractSome of the best-performing high-temperature magnets are Sm–Co-based alloys with a microstructure that comprises an $$\hbox {Sm}_2\hbox {Co}_{17}$$ Sm 2 Co 17 matrix and magnetically hard $$\hbox {SmCo}_5$$ SmCo 5 cell walls. This generates a dense domain-wall-pinning network that endows the material with remarkable magnetic hardness. A precise understanding of the coupling between magnetism and microstructure is essential for enhancing the performance of Sm–Co magnets, but experiments and theory have not yet converged to a unified model. Here, transmission electron microscopy, atom probe tomography, and nanometer-resolution off-axis electron holography have been combined with micromagnetic simulations to reveal that the magnetization state in Sm–Co magnets results from curling instabilities and domain-wall pinning effects at the intersections of phases with different magnetic hardness. Additionally, this study has found that topologically non-trivial magnetic domains separated by a complex network of domain walls play a key role in the magnetic state by acting as nucleation sites for magnetization reversal. These findings reveal previously hidden aspects of magnetism in Sm–Co magnets and, by identifying weak points in the microstructure, provide guidelines for improving these high-performance magnetic materials.

The Coercivity Mechanisms in Sm(CoFeCuZr)z Nanocrystalline Magnets: Nucleation x Pinning

2008 ◽  
Vol 591-593 ◽  
pp. 891-895
Author(s):  
Marcos Flavio de Campos
Keyword(s):  
Particle Size ◽  
Grain Size ◽  
Domain Walls ◽  
Anisotropy Field ◽  
Magnetization Curves ◽  
Main Argument ◽  
Magnetic Reversal ◽  
Initial Susceptibility ◽  
The Difference ◽  
Coercivity Mechanism

It is discussed the difference between the magnetic reversal mechanisms: i) coherent rotation, ii) nucleation, iii) unpinning of domain walls. The main argument to suggest pinning as the coercivity mechanism of Sm(CoFeCuZr)z magnets is the low initial susceptibility of magnetization curves of thermally demagnetized magnets. However, coherent rotation also implies in low initial susceptibility, since the grain size of the magnets is near the single domain particle size. It is unlikely that pinning could be the coercivity mechanism in this case, since the anisotropy field of Sm2Co17 phase is 65 kOe, whereas the coercivity of magnets can be higher than 40 kOe. Such coercive field of 60% of the anisotropy field indicates coherent rotation as mechanism. A model for describing the abnormal coercivity behavior in Sm(CoFeCuZr)z magnets is proposed.

The Critical Volume for Nucleation

2010 ◽  
Vol 660-661 ◽  
pp. 279-283 ◽  
Author(s):  
Marcos Flavio de Campos ◽  
José Adilson de Castro
Keyword(s):  
Grain Size ◽  
Domain Wall ◽  
Legendre Polynomials ◽  
Domain Walls ◽  
Magnetocrystalline Anisotropy ◽  
Critical Volume ◽  
Recoil Effect ◽  
Magnetostatic Energy ◽  
Reverse Magnetization

In magnets based in phases with high magnetocrystalline anisotropy like Nd2Fe14B or SmCo5 there is a competition between magnetostatic energy and domain wall energies. If the grain size is large, the formation of domain walls is energetically favorable. When the formation of domain walls is an unfavorable process, coercivity is larger. A better comprehension of this phenomenon is possible if the energy necessary for the first domain wall formation is properly evaluated. To address this problem, the magnetostatic energy of a sphere magnetized in two opposite directions, separated by a domain wall, is calculated using Legendre Polynomials. The data allow the determination of the reversible volume for nucleation. It is predicted a “recoil effect”, the magnetization may be reversible until a given volume of reverse magnetization.

Nd Rich Nd-Fe-B Tailored for Maximum Coercivity

1999 ◽  
Vol 577 ◽  
Author(s):  
Er. Girt ◽  
Kannan M. Krishnan ◽  
G. Thomas ◽  
C. J. Echer ◽  
Z. Altounian
Keyword(s):  
Domain Wall ◽  
Coercive Field ◽  
Magnetization Curves ◽  
Pinning Mechanism ◽  
Initial Magnetization ◽  
Domain Wall Pinning

ABSTRACTThe coercive field, He, in rapidly quenched Nd-Fe-B was found to increase for samples with excess of Nd. In addition, Hc, strongly depends on the Fe/B ratio, increasing from 1.67 T for Fe/B = 1.07 to 2.05 T for Fe/B = 14.6 in Nd30(Fe,B)70. The increase in Hc seems to correlate with an increase of the γ-Nd phase in the sample. The initial magnetization curves of Nd30(Fe,B)70 show that the domain wall pinning plays a more important role as the Fe/B ratio increases. Thus, γ-Nd may play an important role in promoting a pinning mechanism. The excess of Nd in rapidly quenched Nd-Fe-B samples was also found to promote growth of Nd2Fe14B grains elongated in shape.

The Coercivity Mechanisms in Sm(CoFeCuZr)z Nanocrystalline Magnets: Nucleation x Pinning

2008 ◽  
Vol 591-593 ◽  
pp. 8-12 ◽  
Author(s):  
Marcos Flavio de Campos
Keyword(s):  
Particle Size ◽  
Grain Size ◽  
Domain Walls ◽  
Anisotropy Field ◽  
Magnetization Curves ◽  
Main Argument ◽  
Magnetic Reversal ◽  
Initial Susceptibility ◽  
The Difference ◽  
Coercivity Mechanism

It is discussed the difference between the magnetic reversal mechanisms: i) coherent rotation, ii) nucleation, iii) unpinning of domain walls. The main argument to suggest pinning as the coercivity mechanism of Sm(CoFeCuZr)z magnets is the low initial susceptibility of magnetization curves of thermally demagnetized magnets. However, coherent rotation also implies in low initial susceptibility, since the grain size of the magnets is near the single domain particle size. It is unlikely that pinning could be the coercivity mechanism in this case, since the anisotropy field of Sm2Co17 phase is 65 kOe, whereas the coercivity of magnets can be higher than 40 kOe. Such coercive field of 60% of the anisotropy field indicates coherent rotation as mechanism. A model for describing the abnormal coercivity behavior in Sm(CoFeCuZr)z magnets is proposed.

Nanoscale Ferroelectric Switching: A Method to Inject and Study Non-equilibrium Domain Walls

Domain Walls ◽  
2020 ◽  
pp. 245-270
Author(s):  
A. V. Ievlev ◽  
A. Tselev ◽  
R. Vasudevan ◽  
S. V. Kalinin ◽  
A. Morozovska ◽  
...  
Keyword(s):  
Domain Wall ◽  
Domain Walls ◽  
Domain Switching ◽  
Single Domain ◽  
Detailed Understanding ◽  
Ferroelectric Capacitor ◽  
Efficient Approach ◽  
On Demand ◽  
Ferroelectric Switching ◽  
Non Equilibrium

This chapter focuses on the electric field-induced formation of a single nanoscale polarization domain, emphasizing that nucleation, growth, and annihilation of such a domain enables injection of non-equilibrium domain walls. The focus on nanoscale domains is motivated in large part by advances in scanning probe microscopy (SPM), where the ever-increasing drive to improve spatial resolution was met by a natural reduction of the size of one of the electrodes in a ferroelectric capacitor down to nanoscale dimensions. In this case, the process of ferroelectric switching becomes dominated by the nucleation of a single domain of the opposite polarization. Once allowed to equilibrate, the end-result of the single-domain switching is injection of a new domain wall(s) into the original ferroelectric volume. Likewise, reversing the polarization under the probe will in general eliminate the domain wall(s). The nanoscale ferroelectric switching becomes, therefore, an efficient approach to inject and erase DWs on-demand. However, its primary value may be in facilitation of detailed understanding of the DW injection mechanisms as well as investigation of the range of possible DW configurations, that can be injected up to the highest fields achievable in a given material.

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