Structural and magnetic properties of NiAs-type FeSe and related alloy layers

A single phase of β-FeSe was obtained under Se-rich conditions (β-FeSey: y ≧ 1.15) using pulsed laser deposition. The excess Se content in the layers resulted in a decrease of the unit cell volume owing to the nonstoichiometric composition. However, β-FeSey layers did not show any remarkable change of magnetic properties with the exception of decreased saturation magnetization. On the other hand, doping with Cr ions caused lattice distortions along the c-axis direction following a change of the crystallographic superstructure from 4c to 3c types, as confirmed by x-ray diffraction and temperature-dependent magnetization. As a consequence, high coercivity and high anisotropy of in-plane magnetism at 300 K were observed in Cr-rich β-Fe1−xCrxSe1.28 (x = 0.166) layers. Finally, the authors confirmed a correlation between electron transport and magnetism in β-Fe1−xCrxSe1.28 layers from the results of temperature-dependent resistivity and Hall measurements.