Demagnetizing Field Caused by Specimen End Gaps in Electromagnet Measurements of Permanent Magnet Materials

The midplane and volume-averaged demagnetizing factors, N
_mid
and Nvol, for a uniformly magnetized cylinder of length l
_s
and radius r
_s
clamped in the pole gap of an electromagnet with end gaps of total length d
_s
are calculated as functions of d
_s
/l
_s
and l
_s
/(2r
_s
) and used for converting the measured magnetization-field curves of an Alnico specimen for different values of d
_s
. The maximum d
_s
/l
_s
allowed for permanent magnet measurements stated in IEC and ASTM standards are discussed.