Investigation of LaMn2 − xFexSi2 (0 ≤ x ≤ 1.2) by magnetic measurements and neutron diffraction

The various magnetic structures and phase transitions in the LaMn2 − xFexSi2 system have been thoroughly studied by X-ray powder diffraction, magnetic measurements and powder neutron diffraction. The substitution of Fe for Mn leads to a decrease in the lattice parameters and the magnetic interactions in the Mn sublattice crossover from a ferromagnetic character to an antiferromagnetic one. For the x = 0.475 sample, a field-induced metamagnetic transition from canted antiferromagnetism to canted ferromagnetism occurs at about 3 kOe. The magnetic structures of the LaMn2 − xFexSi2 compounds with x = 0.2, 0.475, 0.5, 0.7 and 1.0 have been determined between 2 and 450 K by neutron diffraction. A typical SmMn2Ge2-like magnetic behavior is observed for the x = 0.475 sample. The magnetic phase transition from ferromagnetism to antiferromagnetism for this sample occurs at the intra-layer Mn-Mn distance dMn-Mna=2.89Å. This value exceeds the well-known corresponding threshold value dMn-Mna=2.87Å in the RMn2X2 compounds. The results are summarized in the LaMn2 − xFexSi2 magnetic phase diagram.