The magnetic properties of alloys having the compositions Mn60AlxZn20-xC20and Mn60GaxZn20-xC20

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Abstract
In the alloys Mn60Al20C20 and Mn60Zn20C20 the Bohr magneton number per manganese atom for the ferromagnetic state differs by 0.32, being greater in the zinc alloy. It was thought that this difference could be accounted for by the difference in valencies between Al and Zn, the extra valency electron of the aluminium atom over that of zinc causing a reduction of one Bohr magneton per unit cell, corresponding to 0.33 Bohr magneton per manganese atom. If this were the case then a simple variation of Bohr magneton number might be expected in the alloy system Mn60Al x Zn20-xC20. In addition, since the alloy Mn60Zn20C20 possesses a transformation at -42°c (when it becomes an antiferromagnetic substance with a complex magnetic structure) whereas the aluminium alloy shows no such transition, measurements on the quaternary alloys should illustrate how this transition is dependent on the electron concentration of the corner atom in the unit cell. The results show a complex behaviour which points against any simple valency mechanism controlling the ferromagnetic properties. Although the lattice parameter of the quaternary alloys varies linearly with Zn-Al content, both the ferromagnetic and antiferromagnetic moments are educed when aluminium partially replaces zinc in Mn60Zn20C20. The ferromagnetio-antiferromagnetic transition moves to lower temperatures and attains 0°k for the composition Mn60Al5.5Zn14.5C20. For aluminium contents greater than 5.5% the alloys show only ferromagnetic properties and the saturation moment then increases with increasing Al content. However, at 10% Al the alloys contain two phases and further magnetic measurements are unrewarding. Similar measurements over a more restricted range of composition were made on alloys of the form Mn60GaxZn20-xC20 and gave results in agreement with those for the Al-Zn alloys.

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