Flux jumps, second magnetization peak anomaly, and the peak effect phenomenon in single crystals ofYNi2B2CandLuNi2B2C

Abstract

We present magnetization measurements in single crystals of the tetragonal $\mathrm{Y}{\mathrm{Ni}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ compound, which exhibit the phenomenon of peak effect as well as the second magnetization peak anomaly for $H>0.5\phantom{\rule{0.3em}{0ex}}\mathrm{T}$ $(H\ensuremath{\Vert}c)$. At the lower field $(50\phantom{\rule{0.3em}{0ex}}\mathrm{mT}<H<200\phantom{\rule{0.3em}{0ex}}\mathrm{mT})$, we have observed the presence of flux jumps, which seem to relate to a structural change in the local symmetry of the flux line lattice (a first-order reorientation transition across a local field in some parts of the sample, in the range of 100 to 150 mT). These flux jumps are also observed in a single crystal of $\mathrm{Lu}{\mathrm{Ni}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ for $H\ensuremath{\Vert}c$ in the field region from $2\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}25\phantom{\rule{0.3em}{0ex}}\mathrm{mT}$, which are compatible with the occurrence of a reorientation transition at a lower field in a cleaner crystal of this compound, as compared to those of $\mathrm{Y}{\mathrm{Ni}}_{2}{\mathrm{B}}_{2}\mathrm{C}$. Vortex phase diagrams drawn for $H\ensuremath{\Vert}c$ in $\mathrm{Lu}{\mathrm{Ni}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ and $\mathrm{Y}{\mathrm{Ni}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ show that the ordered elastic glass phase spans a larger part of $(H,T)$ space in the former as compared to latter, thereby, reaffirming the difference in the relative purity of the two samples.