The Stacking fault energy (SFE) is an important parameter for metals and alloys. The plastic deformation behavior of face centered cubic (FCC) metals and alloys is directly related to the SFE values. The several methods for determining SFE are critically discussed. The values reported in the 1960s and early 1970s are, in general, 20-30% overestimated. The node dislocation method, due to Whelan, overestimates the SFE. The method based on the critical resolved shear stress is not reliable. The most accurate method is the direct observation of dissociated partials by weak beam in TEM or using HREM (High resolution electron microscopy). Indirect methods based in X-Ray Diffraction and texture may provide reasonable estimates since reliable SFE values of reference metals are available. Selected SFE values for Ni, Cu, Ag, Cu and Al are presented.

In the case of the modeling of sintering and heat treatments, the diffusion coefficients are an essential input. However, experimental data in the literature about diffusion coefficients for rare-earth transition metal intermetallics is scarce. In this study, the available data concerning diffusion coefficients relevant for rare-earth transition metal magnets are reviewed and commented. Some empirical rules are discussed, for example the activation energy is affected by the size of the diffusing impurity atom. Diffusion coefficients for Dy, Nd and Fe into Nd2Fe14B are given according an Arrhenius equation D=D0exp (-Q/RT). For Dy diffusion into Nd2Fe14B, Q 315 kJ/mol and D08 . 10-4m2/s.

The coercivity of sintered magnets like barium ferrite (BaFe12O19), samarium-cobalt (SmCo5) or neodymium-iron-boron (Nd2Fe14B) is largely affected by the grain size. A method to evaluate coercivity behavior as function of the crystalline orientation, including also the effects of grain size and lattice defects, is presented. Expressions were deduced to estimate the critical size of nucleus for spontaneous reversion of magnetization. The model indicates that the nucleation in grains of materials with high magnetocrystalline anisotropy only can begin by domain rotation. The model also predicts that the surface condition of grains is very important for the coercivity. A qualitative explanation is offered for the fact that materials with higher coercivity (or with smaller grain size) tend to follow an angular dependence of the coercivity similar to that given by the Stoner-Wohlfarth model, while materials with lower coercivity (or with larger grain size) tend to follow an angular dependence of the coercivity similar to 1 / cos theta.

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.

Loss separation has fundamental importance for optimizing the magnetic material for a given frequency of operation. The loss separation model assumes the existence of two main terms: one due to the hysteresis at the quasi-static situation with frequency less than 0.01 Hz and another dynamic, due to high frequency eddy currents. In this study, it is discussed the physical reasoning behind the loss separation model. Magnetic Barkhausen Noise can be a valuable tool for better understanding the physics of loss separation.