Proc. Roy. Soc A

The magnetic anisotropy of cobalt

W. Sucksmith, F.R.S. and J. E. Thompson

A modified form of the magnetic balance previously designed by one of us, 
is described. In this apparatus the gradient is made independent of the 
magnetizing field. With such an apparatus measurements have been made on 
the variation of the intensity of magnetization with magnetic field for 
single-crystal specimens cut along appropriate crystal axes, both for the 
hexagonal clos-packed and face-cetered cubic cobalt. Such measurements 
enable the magnetic anisotropy constants to be determined.
The nature of the phase change from close-packed hexagonal to 
face-centred cubic occuring at about 400 deg C is such that single 
crystals can be cut at room temperature, which will transform to give 
single crystals of known orientation in the face-centred cubic phase.
The values of the magnetic anisotropy constants for the hexagonal phase 
for various temperatures are compared with those of earlier determinations 
and fair agreement is found.
Measurements on the face-centered cubic phase were made every 50 deg C in 
the temperature range 500 deg C to 1000 deg C; at the latter temperature 
the material became magnetically isotropic.
For face-centred cubic cobalt it was found that the crystal directions in 
order of increasing difficulty magnetization are [111], [110] and [100], 
as in the case for nickel. Moreover, the value of the anisotropy constant 
k_1 obeys the same empirical law, giving the variation with temperature, 
as nickel. The similarity in the magnetic behaviour of these two 
ferromagnetics having the same crystal structure is thus evident.