Magnetic and Chemical Order in Pd2MnAl in Relation to Order in the Heusler Alloys Pd2MnIn, Pd2MnSn, and Pd2MnSb

Abstract

The chemical and magnetic structures of the alloy Pd2MnAl, determined from magnetic and neutron diffraction measurements, are described, and compared with results recently obtained for the alloys Pd2MnIn, Pd2MnSn, and Pd2MnSb. Pd 2 MnSn and Pd2MnSb have the Heusler (L21) structure, and are ferromagnetic with Curie temperatures of 189°K and 247°K, and magnetic moments, confined to the Mn atoms, of 4.23μB and 4.40μB, respectively. Pd2MnIn may be obtained in ordered (L21) and partially disordered (B2) forms by slow-cooling or quenching, respectively. The ordered alloy is antiferromagnetic with a Néel temperature of 142°K and a magnetic moment of 4.3μB per Mn atom. The magnetic moments are aligned in ferromagnetic (111) planes, with neighbouring planes oriented antiparallel as in NiO. In the partially disordered regions the Pd atoms remain ordered, but disorder occurs between the Mn and In atoms resulting in a B2, CsCl type, structure. The Mn atoms are still antiferromagnetically aligned, but on a magnetic unit cell of reduced size consistent with the change in chemical order. Pd 2 MnAl has the B2 chemical structure, and a magnetic structure identical to that of the B2 regions of Pd2MnIn. The alloy has a Néel temperature of 240°K, and a magnetic moment of 4.4μB/Mn atom.