Physics of Magnetism

82 CHAPTER 8. SOME BASIC CONCEPTS AND UNITS

in kOe in the older units can be compared easily with values of in tesla in modern SI

units.

Magnetically hard materials are characterized by a strong preference of the magneti­

zation for one of the crystallographic directions. In this direction, the full magnetization is

already reached in comparatively low field strength, whereas much higher field strengths

are needed in the other (hard) directions. Examples of measurements revealing this property

are shown in Fig. 8.3. It will be clear that the difference in magnetic response between the

various directions is more distinct in plots of J or M versus H than in plots of B versus H.

In order to exclude demagnetization effects, such measurements are preferentially made on

long cylinders of the material with the long axis cut in the various crystallographic directions

considered.

the primacy of

Before leaving this chapter we will briefly mention the existing dilemma between

and For this reason we have summarized Maxwell’s equations and

several other related equations in Table 8.3. When inspecting Maxwell’s equations one

may notice two types of analogies between the electric and magnetic quantities: (i) The

distinction according to the structure of the differential operators (curl and div) leads to the

correspondences and In this picture, the primacy of H is based on fictive

magnetic surface poles or magnetic charges traditionally used in magnetostatics by analogy

equations leads to the correspondences and

appropriate to consider the magnetic induction or magnetic flux density

suggesting that it is more

as the field in

matter.

with electrostatics; (ii) by contrast, the distinction by homogeneous and inhomogeneous

the primary magnetic field is

In the codification of the field quantities of Faraday, Maxwell, and their contemporaries,
taken as the magnetizing force, now called field strength. The
points to the status of a variable quantity that is determined
by the sum of and
However, as stated in (ii) above, the field within magnetized matter is not

and corresponds to the analogy mentioned under point (i) above.

term magnetic induction for

but since