Magnetic and structural properties of DyMn2Hx (0≤x≤4.2)

Abstract

The magnetic properties of Dy(57Fe0.01Mn0.99)2Hx compounds were investigated by means of 57Fe Mössbauer spectroscopy and temperature dependent magnetic susceptibility (DC, AC) and magnetisation measurements. Their structural properties in the temperature range 70 K≤T≤400 K were studied by means of powder X-ray diffraction. It was found that, at room temperature, the lattice parameters increase continuously upon hydrogen absorption in the 0.8≤x≤3.5 range and the cubic C15 crystal structure is preserved. At 70 K the system differentiates into several distinct hydride phases and two-phase ranges. The lattice expansion together with the chemical effect of hydrogen results in dramatic changes in the properties of the hydrides as compared to the host compound. By means of 57Fe Mössbauer spectroscopy, values of the average isomer shifts at 4.2 and 300 K and the average hyperfine fields at 4.2 K were determined. From isomer shift changes at room temperature, the relative importance of the volume expansion and band effects due to hydrogen absorption were deduced. A nonlinear increase of the magnetic ordering temperatures TM versus x and an abrupt increase of the average hyperfine fields for x≥2.5 were also found. Based on TM values for Y(57Fe0.005Mn0.995)2Hx as reference the magnitude of the 4f–3d indirect interaction was inferred. In addition, a strong decrease of this interaction with increasing x (resulting in its cancellation for x>2.8) and a weak dependence on the Dy–Mn distance are clearly shown.