Hysteresis Modeling of NdFeB Magnets with High Nd

2016 ◽  
Vol 869 ◽  
pp. 585-590 ◽  
Author(s):  
Marcos Flavio de Campos ◽  
Fernanda A. Sampaio da Silva ◽  
José Adilson de Castro
Keyword(s):  
Particle Size ◽  
Grain Size ◽  
Grain Boundaries ◽  
Paramagnetic Phase ◽  
Single Domain ◽  
Hysteresis Model ◽  
Ndfeb Magnets ◽  
Single Domain Particle ◽  
Hysteresis Curves ◽  
Hysteresis Modeling

The Stoner-Wohlfarth hysteresis model can describe very well the hysteresis curves since the assumptions of the model are compatible with the studied samples. These conditions are (i) single domain particle size and (ii) inexistence of interactions between the particles. These conditions are obtained in Nd2Fe14B magnets with nanocrystalline grain size below 200 nm and with high Nd, which promotes a paramagnetic phase at the grain boundaries. In the present study, both isotropic and anisotropic NdFeB magnets are modeled.

Squareness of NdFeB Stoner-Wohlfarth Hysteresis

2014 ◽  
Vol 802 ◽  
pp. 601-606
Author(s):  
Marcos Flavio de Campos ◽  
Fernanda A.S. da Silva ◽  
José Adilson de Castro
Keyword(s):  
Particle Size ◽  
General Result ◽  
Anisotropy Constant ◽  
Single Domain ◽  
Single Domain Particle ◽  
Hysteresis Curves ◽  
Intrinsic Coercivity ◽  
Grain Diameter

Hysteresis curves were calculated according the Stoner-Wohlfarth (SW) model using values of K2/K1from zero up to 0.25 (where K2is the 2ndorder anisotropy constant and where K1is the 1storder anisotropy constant). The SW calculations assume Nd2Fe14B nanocrystalline magnets with single domain particle size (grain diameter less than 150 nm). The effect of K2on several index of merit of magnets as BHmaxand squareness are discussed. As a general result, increasing K2, the intrinsic coercivity increases. However, the increase of K2almost does not improve the BHmaxof isotropic magnets. It is found that the effect of the K2/K1ratio is coupled with the effect of texture, i.e., the effect of K2is more significant for pronounced texture.

Application of Micromagnetic Models for Barium Ferrite Magnets

2015 ◽  
Vol 820 ◽  
pp. 199-204 ◽  
Author(s):  
Marcos Flavio de Campos ◽  
Fernanda A. Sampaio da Silva
Keyword(s):  
Particle Size ◽  
Grain Size ◽  
Coercive Force ◽  
Total Energy ◽  
Barium Ferrite ◽  
Magnetocrystalline Anisotropy ◽  
Single Domain ◽  
Square Root ◽  
Single Domain Particle ◽  
Magnetostatic Energy

The applicability of micromagnetics for phases with high magnetocrystalline anisotropy as barium ferrite Ba2Fe12O19and Nd2Fe14B is discussed. The Stoner-Wohlfarth model is very suitable for such phases, and also for PtFe and PtCo. It was discussed how to take into account the total energy of the system for grain size above the single domain particle size. For this situation of large grain size, the net magnetostatic energy of the system cannot be neglected. From energy considerations, it follows that the coercive force should decrease with the inverse of the square root of the grain size.

Nucleation as Coercivity Mechanism in NdFeB Magnets

2014 ◽  
Vol 775-776 ◽  
pp. 437-442 ◽  
Author(s):  
Marcos Flavio de Campos
Keyword(s):  
Particle Size ◽  
Grain Size ◽  
Domain Wall ◽  
Coercive Field ◽  
Square Root ◽  
Ndfeb Magnets ◽  
Single Domain Particle ◽  
Wall Displacement ◽  
Melt Spun ◽  
Coercivity Mechanism

In the first part of this article, the SW-CLC (Stoner-Wohlfarth with CLC modification) model is discussed for nanocrystalline magnets, as melt-spun exchange coupled NdFeB. In the second part, the effect of grain size of coercivity for large grain size, above the single domain particle size, is addressed. The Kondorsky law observed for large grain size only can be due to domain wall displacement phenomena, where there is nucleus expansion. There are two main situations, one for nanocrystalline grain size, where the SW-CLC model is obeyed, and other for large grain size, where the coercive field decreases proportionally to the square root of the grain size.

scholarly journals Effect of Mechanical Milling on the Magnetic Properties of SrFe12O19

2015 ◽  
Vol 12 (1) ◽  
pp. 28-30
Author(s):  
I Bsoul
Keyword(s):  
Particle Size ◽  
Magnetic Properties ◽  
Crystallite Size ◽  
Mechanical Milling ◽  
Single Phase ◽  
Strontium Ferrite ◽  
Single Domain ◽  
Single Domain Particle ◽  
Ferrite Sample

In this work, a single phase strontium ferrite sample was mechanically milled for 60 h. It has been found that the crystallite size reduced by 85%. A dramatic drop (from 4500 to 1600 Oe) in the coercive filed was also observed. The observed reduction in the coercivity was attributed to the reduction of the single domain particle size.

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.

Effect of Grain Size on the Coercivity of Sintered NdFeB Magnets

2010 ◽  
Vol 660-661 ◽  
pp. 284-289 ◽  
Author(s):  
Marcos Flavio de Campos
Keyword(s):  
Particle Size ◽  
Grain Size ◽  
Energy Balance ◽  
Coercive Field ◽  
Domain Walls ◽  
Dissipative Process ◽  
Ndfeb Magnets ◽  
Grain Sizes ◽  
A Value ◽  
Energy Balance Models

Sintered NdFeB magnets typically exhibit grain size above 2 micrometers, a value above the single domain particle size (~0.3 micrometers). It is discussed how to obtain relationships between grain size and coercivity with energy balance models, considering formation and annihilation of domain walls as a dissipative process. In the case of nanocrystaline magnets, the Stoner-Wohlfarth model is very suitable. For larger grain sizes, the contribution of the magnetostatic energy of each grain has to be considered. From the concept of meta-stability of domains and domain walls structure, a relation between coercive field and grain size can be estimated.

Magnetic force microscopy of combined reaction-processed polycrystalline equiatomic bulk L10 FePd

2009 ◽  
Vol 24 (8) ◽  
pp. 2677-2687 ◽  
Author(s):  
Paul R. Ohodnicki ◽  
Anirudha Desphande ◽  
Jorg M.K. Wiezorek ◽  
Timothy J. Klemmer
Keyword(s):  
Grain Size ◽  
Grain Boundaries ◽  
Domain Structure ◽  
Magnetic Force Microscopy ◽  
Magnetic Force ◽  
Single Domain ◽  
Interaction Domain ◽  
Force Microscopy ◽  
Average Grain Size ◽  
Interaction Domains

In this work, the correlation between magnetic-domain structure and microstructure in combined reaction-processed equiatomic L10 FePd has been investigated using magnetic force microscopy. The microstructure consisted of approximately equiaxed grains with an average grain size of ∼1 μm and a grain size distribution ranging from below the theoretical critical domain size (Dcrit∼0.2–0.3 μm) up to approximately 5 μm in diameter. The domain structure was characterized as “mixed” in nature, consisting of smaller single-domain grains, larger multidomain grains, and a larger scale interaction domain structure encompassing many grains. The domain boundaries separating interaction domains tended to lie along grain boundaries, and it is proposed that the observed interaction domains should be considered in descriptions of the magnetization and magnetization reversal behavior of this material. In particular, pinning of interaction domain walls by intragranular features of the microstructure such as grain boundaries and single-domain grains could play a role in the measured coercivities.

Effect of Particle Size on the Zener Limit: A Monte Carlo Simulation Approach

2012 ◽  
Vol 560-561 ◽  
pp. 152-155 ◽  
Author(s):  
Kalale Raghavendra Rao Phaneesh ◽  
Anirudh Bhat ◽  
Gautam Mukherjee ◽  
Kishore T. Kashyap
Keyword(s):  
Monte Carlo Simulation ◽  
Particle Size ◽  
Grain Size ◽  
Monte Carlo ◽  
Grain Boundaries ◽  
Grain Growth ◽  
Second Phase ◽  
Particle Sizes ◽  
Second Phase Particles ◽  
Average Grain Size

2D Potts model Monte Carlo simulation was carried out on a square lattice to investigate the effects of varying the size of second phase particles on the Zener limit of grain growth, in two-phase polycrystals. Simulations were carried out on a 1000^2 size matrix with Q-state of 64, dispersed with second phase particles of various sizes and surface fractions, and run to stagnation. Different grain growth parameters such as mean grain size, largest grain size, fraction of second phase particles lying on grain boundaries, etc., were computed for the pinned microstructures. The pinned average grain size or the Zener limit increased with increase in particle size, as per the classic Smith-Zener equation. The Zener limit scaled inversely with the square root of the particle fraction for all particle sizes, while it scaled exponentially with the fraction of second phase particles lying on the grain boundaries (ϕ), for all particle sizes tested.

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