Magnetic properties of Dy-Zr nanocomposites

As part of a search for materials which exhibit enhanced magnetocaloric effect, the magnetic properties of amorphous Dy₇₀Zr₃₀ and Dy₃₀Zr₇₀ alloys were investigated in the temperature range of 5--300 K and at magnetic fields up to 7 T. The results show that these materials can be described as nanocomposites, with interacting clusters below a critical temperature TF and simple paramagnetism above 120 K. Below 120 K the magnetization is history dependent up to a critical field determined by the composition. Field cooling results in a shift of the low-temperature hysteresis loop along the magnetization axis, without influencing the shape. The magnetic entropy change peaks at the same temperature for both compositions, with a composition-dependent peak height, offering a unique tunability of the magnetocaloric effect. The results are interpreted in terms of existing theories of cluster glasses.