Magnetic phase diagram of the intermetallic LaMn2−xCuxSi2 silicides

Abstract

X-ray diffraction (XRD), differential scanning calorimetry (DSC) techniques and AC magnetic susceptibility measurements have been carried out on polycrystalline LaMn2−xCuxSi2 (0.0≤x≤1.0) silicides to investigate how the ferromagnetic and antiferromagnetic regions in LaMn2Si2 are affected by Cu substitution. All compounds crystallize in the ThCr2Si2-type structure with the space group I4/mmm. Substitution of Cu for Mn leads to a linear decrease in the lattice constant c and the unit-cell volume V and a linear increase in the lattice constant a. In all the samples, ferromagnetic interactions within the Mn sublattice take place below the Curie temperature TC(Mn). The onset of ferromagnetism at TC(Mn) decreases with the copper content from 308 (x=0) to 82K (x=1). The temperature dependence of the AC susceptibility shows a distinct feature for x≤0.6 at temperatures below TC(Mn). These samples have a mixed state composed of ferromagnetic and antiferromagnetic phases. The samples with x≤0.2 have a Néel temperature associated with antiferromagnetic behavior above room temperature. A magnetic phase diagram as a function of Cu concentration in LaMn2−xCuxSi2 has been constructed.