Magnetic order in the AuMn alloy derivatives Au2(Mn,Z)2where Z is Al, Cu, Ga, In or Zn

The moment direction in antiferromagnetic AuMn has been redetermined using neutron diffraction techniques, giving a revised value (4.6±0.1)μ B for the moment per Mn. When the moment bearing Mn is diluted randomly with Zn in Au 2 Mn 2-l Zn l the alloys remain antiferromagnetic until a transition to paramagnetism occurs at a limiting composition Au 2 Mn 0.6 Zn 1.4 . However, when the solute is Al, Ga or In the solute atoms order chemically with Mn so that the dilution of the Mn moments is then nonrandom; in Au 2 Mn 2-l Al l , the ground state magnetic structure progresses from antiferromagnetic to ferromagnetic to helimagnetic. Experimental observations on the magnetic ordering in these alloys can largely be interpreted in terms of the changing probabilities of Mn neighbours in particular coordination shells. However, the results for Cu are anomalous and seem to demand an assumption that the Cu atoms cause changes in the magnitude of the coupling between individual pairs of Mn spins.