Grain energies, anisotropy

An alternative mechanism is based on the local stresses that are caused by the development of axial anisotropy within the grains as they cool below Tc. Lower-energy domain configurations may be generated by phonon action at room temperature and might be assisted by a high concentration of V0. Another... 

To maintain thermal stability, hence a condition EB/kBT= In (for) needs to be fulfilled. For z = 10 years storage, 109-10u Hz [28] and ignoring dispersions, i.e. assuming monodisperse particles, this becomes Es/kBT= 40-45. Reversal for isolated, well-decoupled grains to first order can be described by coherent rotation over EB. This simple model, as first discussed by Stoner and Wohlfarth in 1948 [29], considers only intrinsic anisotropy and external field (Zeeman) energy terms. For perpendicular geometry one obtains the following expression ... 

Figure 8. Scaling of areal density (AD) with anisotropy energy density Ku using room temperature bulk data from Table 2 and elongated cubes with constant grain aspect ratio 5/Dp = 4 (case d) (the dashed line is a linear fit of the data to the power one).

Figure 2 schematically illustrates how the local anisotropies are averaged out for D < L0. In this illustration we have modelled the local anisotropy energy density for each individual grain by... 

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