Magnetic phase transition and magneto-elastic coupling in Fe1+xCr2-xSe4 (x = 0.0 - 0.50)

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A comprehensive study of the structural and magnetic properties of the series Fe1+xCr2-xSe4 (with x = 0.0, 0.10, 0.25, and 0.50) is carried out by magnetization, x-ray photoemission spectroscopy (XPS), and temperature dependent x-ray diffraction measurements. The parent compound (x = 0.0) undergoes a paramagnetic to antiferromagnetic (AFM) transition at TN ∼ 220 K. As x increases, the XPS spectra indicate that the concentration of Fe3+ increases, which leads to an increase in effective moment and the evolution of ferrimagnetic (FRI) ground state through an intermediate state where both AFM and FRI phases co-exist. The compound with x = 0.50 exhibits a complete FRI ground state (TC ∼ 210 K) and shows a dip in the magnetic susceptibility at a temperature Tdip ∼ 170 K. The magnetocaloric effect curves also exhibit anomalies across these temperatures (TN and Tdip). The magnetic ordering in this series of compounds is accompanied by a distortion in the crystal lattice, as evident from the anisotropic variation of lattice parameters.