First order magnetisation processes in Pr2(Co1-xFex)17alloys

The discontinuity in the hard direction magnetisation curve for the alloy Pr
2
(Co
0.6
Fe
0.4
)
17
has been studied over the temperature rauge 5K-300K using a partially aligned polycrystalline sample. By means of the singular point detection technique we have measured the temperature variation of the anisotropy field and also the position of the magnetisation discontinuity. We conclude that the discontinuity is associated with a first-order rotation of the magnetisation vector, and its appearance as temperature is lowered is due to the rapid decrease of the second anisotrcpy constant K
2
to below a negative value K
2
= -K
1
/6. Analysis of the anisotropy constants obtained by Shanley for a Pr
2
(Co
0.8
Fe
0.2
)
17
alloy enable a good estimate to be made of the position of the anomalous discontinuity for this alloy.