An anomalous butterfly-shaped magnetoresistance loop in an alloy, Tb4LuSi3

Magnetic-field (H) induced first-order magnetic transition and the assiciated electronic phase-separation phenomena are active topics of research in magnetism. Magnetoresistance (MR) is a key property to probe these phenomena and, in literature, a butterfly-shaped MR loop has been noted while cycling the field, with the envelope curve lying below the virgin curve in MR versus H plots of such materials. Here, we report an opposite behavior of MR loop for an alloy, Tb4LuSi3, at low temperatures (<<20 K) in the magnetically ordered state. Such an anomalous curve reveals unexpected domination of higher resistive high-field phase in electronic conduction, unlike in other materials where conducion is naturally by low-resistive high-field phase that follows first-order transition. The observed features reveal an unusual electronic phase separation, namely involving high-resistive high-field phase and low-resistive virgin phase.