Equiatomic transition metal alloys of manganese

The structural and magnetic properties of well characterized alloys have been studied in the range from 40 to 66 at. % Pd. The CsCl type, cubic PdMn phase is stable only at high temperatures, homogeneous between ∼40 and∼50 at. % Pd at 685°c, and paramagnetic with 2S Mn = 5·0 ± 0·5 ('spin only’ approximation). The CuAul type, tetragonal PdMn phase is homogeneous in the range from 45 ± 1 to ∼ 65·5 at. % Pd according to temperature, paramagnetic above 825 ± 10°K (∼50 at. % Pd) to 290 ± 10°K (66 at. % Pd) with 2S Mn=4·1 ±0·2 ('spin only’ approximation), and anti ferromagnetic below these temperatures (full range 45±1 to ∼65·5 at. % Pd) with 2S Mn = 4·0 ±0·2, 2S pd<0·2, determined by neutron diffraction. 2S Mn probably decreases slightly below 50 at. % Pd. The magnetic unit cell contains four atoms, and moments of nearest-neighbour Mn atoms are aligned anti-parallel within (001) planes. The magnetic properties appear to depend on exchange interactions between both nearest and next-nearest Mn neighbours, the latter involving indirect Mn-Pd-Mn interactions via d orbitals. The Pd21Mn11 phase occurs below ∼ 480°K from 56·25 to 65·63 at. % Pd. The chemical and magnetic cells both contain 32 atoms; the former is tetragonal. With moments of nearest-neighbour Mn atoms aligned anti-parallel within (001) planes, the chemical ordering produces a ferrimagnetic state. The atomic moments are identical to those of the tetragonal PdMn phase.