User`s manual

7800 Series Hysteresisgraph System User's Manual
2-4 Theory of Operation
Theory Of Operation (Continued)
Continuing to sweep through Negative H, we cross a point where the B vs. H curve crosses the H axis - where B =
0. This point is called Hc, or Normal Coercivity. Further increases in negative H will result in the (B-H) curve
crossing the H axis. At this point, the sample has zero average induction. We have ‘coerced’ the domains from
their earlier, mutually aligned direction, to average out to zero induction. This is called Hci or Intrinsic Coercivity.
At this point, A second quadrant demag curve is complete. Many people will finish their analysis of a magnetic
specimen at this point. Many of the points of significance have already been attained by the time Hci is reached -
Br, Hc, Hci (BHmax), Hk etc. Complete information on these extracted parameters will follow. However, others
will continue to draw the full hysteresis loop by saturating the sample in the negative direction and then
remagnetizing the sample so as to draw the symmetric portion of the loop - if sufficient EM field is available to
saturate the sample in the negative direction within the EM yoke. In many cases, NdFeB and SmCo will not allow
you to draw the major hysteresis loop in the EM yoke since the sample cannot be saturated without the help of a
pulse discharge magnetizer.
This completes our look at 2 and 4 quadrant hysteresis loops.
2.3 YOKE AND MAGNETIZATION CONDITIONS (DIN 50-470-80)
The following data relates to the measurement of yoke and magnetization conditions as specified in DIN 50-470-
80, Paragraph 6. Symbol definitions are provided in Figure 2-2.The results in Table 2-1 were calculated using the
following equation.
1.2
D
dl≥+ ×
(Equation 1)
Results in Table 2-2 were calculated using the following equation.
2
D
l≥×
(Equation 2)
D
l
d
Arrangement of specimen and field measuring
device in the yoke (not to scale)
D = the diameter of a circular pole face.
l = the distance between pole faces.
d = the maximum transverse dimension of the
homogeneous field space perpendicular
to the direction of flux (diameter of
uniform field).
Arrangement.eps
Figure 2-2. Yoke and Magnet Conditions