Antiferromagnetism and Griffith's Phase on Cu doping in U(Mn1−Cu )2Ge2 intermetallics

Abstract

The intermetallics of U(Mn1−xCux)2Ge2 (0.0 ≤ x ≤ 0.2) were synthesised and their magnetic properties and crystal structure were investigated by means of dc magnetization and Neutron Diffraction (ND) measurements. With Cu doping up to x = 0.2, the crystal structure remains the same in tetragonal structure with space group (I4∕mmm m m). Rietveld refinement of the room temperature ND data suggests that the dU−U is greater than Hill’s critical distance ~3.5 Å for all the compounds and altered values of dU−T distance results into modification of the magnetic properties of UMn2Ge2 intermetallic compound. Detailed study reveals inducement of antiferromagnetism at low temperatures, reduction in TC and a Griffith’s phase above ferromagnetic TC in the doped compounds. With increasing Cu, Griffith’s phase becomes more prominent. Replacing Mn with Cu randomly in the lattice gives rise to disorder which results in short range spin - spin correlations leading Griffith’s like phase. Further, decrease of volume and lattice parameter c results in antiferromagnetic interactions leading to AFM order at low temperatures. AFM order progressively gets stronger for higher Cu doping.