Unconventional magnetic and transport properties in Gd1−xLaxMn2Ge2 with two-dimensional arrangement of Mn atoms

Abstract In this paper, we present our recent experimental results of magnetic and transport properties of Gd 1− x La x Mn 2 Ge 2 intermetallic compounds with the ThCr 2 Si 2 -type layered structure. The results obtained indicate that, in GdMn 2 Ge 2 , a first-order transition from a collinear antiferromagnetic to a collinear ferrimagnetic state appears with decreasing temperature at T t3 , below the Neel temperature T N . In Gd 1− x La x Mn 2 Ge 2 compounds with x =0.05 and 0.075, after ordering ferrimagnetically at T t1 , two kinds of first-order transitions from a canted ferrimagnetic to a non-collinear antiferromagnetic state and from a non-collinear antiferromagnetic to a reentrant canted ferrimagnetic state occur at T t2 and T t3 . In Gd 0.925 La 0.075 Mn 2 Ge 2 , a field-induced metamagnetic transition from non-collinear antiferromagnetism to canted ferrimagnetism occurs at relatively low fields, accompanied by fractal like multi-step transitions, the so called “devil's stair-case”. Furthermore, a negative giant magnetoresistance (GMR) effect (Δ ρ / ρ ∼15%) was observed at the field-induced metamagnetic transition. The mechanism of this negative GMR was clarified by comprehensive measurements of the resistivity on single crystals Gd 0.925 La 0.075 Mn 2 Ge 2 and TbMn 2 Ge 2 . With further increasing x , only canted ferrimagnetism appears with a compensation temperature for 0.10 x x >0.50. The phase diagram obtained indicates that the overall magnetism is controlled by the Mn–Mn intralayer distance in the tetragonal c -plane, reflecting the two-dimensional arrangement of Mn atoms.