Enhancement of positive magnetoresistance at the metamagnetic transition in Tb$_{5}$Si$_{3}$

It is well-known that, in the antiferromagnetic systems, at the metamagnetic transition field (H$_{t})$, negative MR [defined as {\{}$\rho $(H)-$\rho $(0){\}}/$\rho $(0) where $\rho $ is the electrical resistivity] is observed. Here we present evidence for the opposite behavior of MR in an intermetallic compound, viz., Tb$_{5}$Si$_{3}$, known to form in Mn$_{5}$Si$_{3}$-type hexagonal structure (space group: P6$_{3}$/mcm). We observe a field-induced ferromagnetic transition in the magnetically ordered state (T$_{N}$= 69 K). The key experimental finding is that, below T$_{N}$, $\rho $ is dramatically enhanced at all temperatures (resulting in large ``positive'' MR) at H$_{t}$, in sharp contrast to the expectation based on common knowledge. This finding bears significant relevance to electron scattering phenomena in general, and in particular in metamagnetic systems.