Spin-glass behavior in YCo10−xNixSi2 with high Ni content

The magnetic properties and the structure of YCo10−xNixSi2 alloys with high Ni content have been investigated by means of measurements of X-ray diffraction, dc magnetization and ac-susceptibility. The samples are basically of single phase (with x=6, 7, 8, 8.5, 9, 10) and adopt the ThMn12 type structure. With x≤7.0, the samples show ferromagnetic behavior below the Curie temperatures. For compounds YCo2Ni8Si2 and YCo1.5Ni8.5Si2, the ac-susceptibility and dc zero-field cooling (ZFC) M(T) curve show a cusp with decreasing temperature, and the dc ZFC and field cooling (FC) M(T) curves in lower fields exhibit thermal irreversibility at low temperatures. The magnetization curves at temperatures below the cusp temperature on the ZFC branches do not saturate in the field range of H≤55 kOe. Furthermore, the hysteresis loops at temperatures below the cusp temperature exhibit no coercivity after ZFC. All these features suggest a spin-glass ordering of the compounds YCo10−xNixSi2 with x equal to 8 and 8.5. The spin-glass behavior can be understood in terms of a competition between ferromagnetic interactions involving close Co–Co neighbors and antiferromagnetic interactions involving more remote Co–Co neighbors.