Also, the magnetization of the magnet is assumed as a linear second quadrant demagnetization curve
[4-6] of the form: [B.sub.m] = [B.sub.r] + [micro.sub.m][H.sub.m] and [micro.sub.m] = [B.sub.r]/[H.sub.c] ; where [B.sub.r] is remanence of magnet, [H.sub.c] coercivity and [micro.sub.m] permeability of magnet.
Nowadays, the new nanoanalytical electron microscopic techniques with atomic resolution allow the creation of precise microstructural models suitable for the numerical micromagnetic calculation of the demagnetization curve including the coercive field value.
The measured demagnetization curve and the simulated curves of directly coupled grains with an average grain misorientation of 45[degrees] and 60[degrees] are shown in Figure 13.
Caption: Figure 8: Comparison of the measured demagnetization curve of the MQU-F melt-spun ribbon with calculated curves for directly coupled [Nd.sub.2][Fe.sub.14]B grains (no-GB) and grains separated by a weakly soft magnetic GB-phase (sm-GB) with [J.sub.s] = 0.43 T and A = 1.0 pJ/T for an average grain misorientation of 45[degrees] and 60[degrees].
Using the Voronoi model structure of isotropically orientated [Nd.sub.2][Fe.sub.14]B grains (Figure 1) with an average grain size of 50 nm and a GB-phase with a thickness of 4 nm-6 nm (Figures 5 and 6) we calculated the demagnetization curves obtained from the numerical finite element micromagnetic simulations depending on the coupling between the grains and the degree of misorientation of the grains.
The calculated demagnetization curves for the pure x-GB with [H.sub.ext] [parallel]  and [J.sub.s] = 0.15 T (Table 3) and for the pure y-GB with [H.sub.ext] [parallel]  and [J.sub.s] = 1.0 T and a GB thickness of 8 nm are shown in Figure 16.
The demagnetization curve
of Nd-Fe-B rare-earth permanent magnet is a straight line.
The magnetic behavior of a magnetized permanent magnet is expected to be defined by the measured demagnetization curve. In our previous work [17-19], we have studied the time-dependent demagnetization of different types of NdFeB-based magnets to find some practical information and a clear connection between the demagnetization curve of a magnet material and the long-term magnetic behavior of a magnet produced from that material.
Standard demagnetization curves are measured in a timescale of seconds and the so-called thermal aftereffect or ageing is not visible in the curves.
A comparison was made of the time-dependent demagnetization behavior of two different sintered NdFeB magnet materials showing different types of demagnetization curves. In magnets produced from a material with a very square JH curve, the losses are negligible until a certain critical temperature is reached.
PerMag covers all aspects ofmagnetostatics, including saturation effects in soft materials and permanent magnets with non--linear demagnetization curves
. The package includes Mesh, an automatic conformal mesh generator with a built-in drawing editor and DXF import capability.
were measured by using a vibrating sample magnetometer (VSM) after magnetizing the ribbons with a pulsed magnetic field of at least 1.5 T.